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Modelled on those transparent balls you can put hamsters in to let them run safely around your home, this is basically the same but built for your fish.
At some point on the sphere is a watertight, screw-on panel which can be removed in order to get the fish inside. To get the fish into the sphere,
you simply push it into the fish's normal aquarium, and the fish will be sucked in along with the the water. Then remove ball from aquarium, dry off with towel, and set the ball on the floor.
Now, I'm pretty sure this next bit won't work, but it almost seems to make a strange kind of sense. As the fish moves toward the edge of the ball, the weight distribution in the ball shifts, and the ball itself shifts with it. Thus your little fishy can swim through your house just as effectively as if you'd flooded the whole place knee-deep in water.
As I said, I'm fairly certain that things won't be that simple, given the fish's swim bladder and its bouyancy and probably lots of other things that I don't know anything about either. I did try to come up with another mechanism for making the ball move with the fish, but the best I could come up with was the equally improbable mechanism of having the water filled-ball surrounded by another slightly larger ball which contains a couple of weighted ball bearings. Attach a magnet to the fish (another potential stumbling block, I'll agree), and as the fish influences the ball-bearings, the ball moves.
Still, even if the fish can't get the Bowl moving itself, the whole setup would make an excellent cat toy.
EcoSphere
http://www.abundant...tore/ecosphere.html
[Shz, Oct 04 2004, last modified Oct 21 2004]
(?) Related in the annotations...
http://www.halfbake...idea/Fish_20Mobiles
Mechanisms for goldfish bowl travel [RayfordSteele, Oct 04 2004, last modified Oct 05 2004]
(???) G-suit
http://www.beyond20...g_00/story_742.html
Using water tubes to counteract G-forces [8th of 7, Oct 04 2004, last modified Oct 21 2004]
(?) Fish Controlled Robotic bowl-movers
http://www.ylem.org...iated/mediated.html
Location of fish is done using IR [stormo, Oct 04 2004, last modified Oct 21 2004]
Propulsion kit for Goldfish Bowl
http://www.halfbake..._20Propulsion_20Kit
shameless plug [roby, Oct 04 2004, last modified Oct 05 2004]
Look what I just found...
http://www.toothpas...ou-have-to-stay.gif
[k_sra, Oct 04 2004, last modified Oct 05 2004]
Walking the goldfish
http://www.amazon.c...51?v=glance&s=books
With a leash and some wheels, you could take him out. I have a signed copy of this book too.... [choaderboy, Oct 05 2004]
(???) Maywa Denki Nonsense Machines
http://www.maywaden.../products/naki.html
the third last idea on the page. [benfrost, Dec 16 2005]
(?) Seth Weiner's Terranaut
http://www.we-make-...archives/007286.php
A different take on freeing goldfish to explore the non-aquatic world. His battery-powered fishbowl-on-wheels moves around the art gallery in a path determined by the direction in which the solitary goldfish swims. Winner of the Bartlebooth award. [jurist, Jul 07 2006]
Kenneth Rinaldo: Augmented Fish Reality
http://www.wired.co...-fish-reality-2004/
Bowl moves in the direction the fish swims in. [jutta, Jul 22 2006, last modified May 23 2014]
Hamster Mech Suit
http://www.popsci.c...s-armored-mech-suit
[theircompetitor, Feb 08 2011]
(???) Idea submitted to Mythbusters
http://community.di...67776/m/86019078701
[doctorremulac3, Feb 14 2011]
Fish on Wheels Video
https://www.youtube...watch?v=YbNmL6hSNKw
[swimswim, Feb 11 2014]
Taking things to their logical extreme
https://gfycat.com/acidicwarpedbaboon
[2 fries shy of a happy meal, Oct 10 2019]
The latest research
https://www.cnn.com...le-lon-orig-mrg.cnn
We be drivin' [RayfordSteele, Jan 11 2022]
[link]
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Excellent concept, just one problem: the fish will *not* be able to propel the ball by swimming about. Moreover, if it could, the water in the bowl would turn over and over, discombobulating the fish. |
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However, your second mechanism is not unlike those rolling eyeballs they sell to children: an inner sphere in an outer sphere filled with water. When you roll them, the eyeballs stay pretty much vertical, a desired effect here. So you could do that. |
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This still provides no motive power to get the goldfish moving. But there's always the cat. |
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It's a very funny image. I guess this one might fall under the "impossible but in an interesting way" heading. |
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Would be a neat way for the goldfish to torment the cat, if it could only remember why it should, or how, or that there was a cat... |
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Put a set of optical sensors on it. When the fish moves out of the central "null zone" to one side of the bowl, little motors rotate the ball in that direction. |
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In a kind of limited "Turing test", I wonder if you could distinguish the motion of the fish from that produced by a random number generator. |
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// Now, I'm pretty sure this next bit won't work, // |
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You're right, it won't. So no roaming, but the fish globe is interesting. |
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Strap fish globe to remote controlled car. Fish! Get the cat, fish! Go! Go! (whhhiiirrrrrrRRRRR!!!!) |
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//the fish will *not* be able to propel the ball by swimming about.//
Simple physics disagrees. This is a nonequilibrium situation. The ball WILL roll, given low enough friction. |
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No it won't. The weight and pressure inside the sphere is the same, no matter where inside the fish is located. |
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Only in static equilibrium, not during acceleration. She rolls! Or rocks and rolls. Well, mainly rocks. |
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Well you're going to have to explain how that will work, then. |
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If the fish swims to one side of the sphere, it has merely displaced water that was already there. There is no change in weight or pressure, nothing to cause motion. The motion of the fish swimming is offset by the movement of the water away from it as it swims. |
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Agreed. Back to the drawing board, lads. |
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Are we going to vote on the laws of physics, then? This fishbowl sphere works in the same way that a child's swing works. You start with your feet off the ground, in equilibrium. Dosen't seem like you could get it swinging, but in fact, you can. |
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No, that's not a good analogy at all. A swing is a pendulum. Once you move it off center, gravity pulls it back. If the fish swims off center, there is no force to recenter it. |
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If the swing was inside a sphere, the sphere would roll to offset the swinging motion. This doesn't apply to the fish, as the fish is not attached to the sphere. |
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I own something similar, though it doesn’t roll. <link> However, creative + amusing + fish = croissant in my book. |
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Maybe an Aibo, or similar robotic dealy with a sealed fishbowl built into it. You could put the tank on some king of swiveling mounts to keep it from moving too much when the robot is running around. If it's important for the fish to be controlling the movement, I suppose you could have sensors to see where the fish moves, and have the robot move in that direction. |
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can you make one for humans? (I think it's time to let my sister out of the cage). |
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I think the fish will have a limited life expectancy since of you seal it in a sphere, there will be no gas diffusion to remove CO2 and replace oxygen. You'll need to incorporate a gas scrubber. |
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As to movement, i think that if the fish swims vigorously, the turbulence and friction between the water and the bowl might produce a small amount of movement but since the fish is neutrally buoyant (electively) the movement of its mass within the water sphere is not going to produce any movement (I agree with [waugs]). |
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I've seen ecospheres - very, very highly recommended. |
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It *will* work - all you need is two concentric glass spheres. In the inner one you have your mouse, happily running about. Between the inner and outer spheres you have your fish, swimming. The locomotive power comes from the mouse; The aesthetics come from the fish. |
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[UB] I've always wanted to master the menace behind Hal's dead-pan computer voice. It's all in the pause. |
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Regarding the idea, it's not at all easy, after all, not many domestic fish like swimming against current. Otherwise, they'd go mad in a tank. Also, machinery or even suction in a tank is a bad idea, unless you want a fish smoothie. |
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Let's say you had a bluefin tuna or a salmon in a tank. You want it to swim without circling the tank. You could generate a water treadmill (not that fish tread)by pumping water in at one end and allowing over-/ out-flow at the other. This set-up is sometimes used to train Olympic swimmers, but it's not fish friendly. If the fish gets tired, it'll get whammed against the back grille, like you were dragging a steel net through the ocean at 35kts. |
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Instead, I propose a vertical vortex. The very large tank is shaped like a hamster wheel, but with smooth periferal walls. One (or both) side is a viewing window. Water jets are injected into the water at the base and if necesary strategic points around the outside. This creates a circular flow. If the fish's food is attached at a fixed point upstream of the bottom, viewers can watch as the tuna powers up to the mark at high speed, snatching it away. |
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If the fish tires and slows, it theoretically could get washed back, and get sloshed around and around like a doll in a washing machine. More likely, it'll learn to cruise up towards the centre of the wheel, where the water flow is slowest. |
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Need to add plenty of slime coating to prevent injury to the fish.
How about a small wheelchair, so it can be the Steven Hawking of fish? |
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Or a sort of piscine Davros ? |
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[FloridaManatee]'s 'water treadmill' is baked. My wife once kept fancy goldfish, one of whom (Stuffy the oranda - the fish were all named after Harpo Marx characters) would position his elf facing into the outlet from the filter / aerator and swim frantically while remaining stationary. After a while, he would relax and let the flow propel him to the far end of the tank. Great to watch. |
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//is not going to produce any movement (I agree with [waugs]).//
<Slamming down her cup of coffee, Pluterday scavenges thru a closet to find a mortarboard. This is now on her head, perched unsteadily over curlers. Pulling a stick a chalk from her sleeve, she rapidly sketches on a blackboard. A sphere on a hard level floor surface filled to the top with water appears, with a neutrally buoyant fish making loops inside along an axis parallel to the floor. Above this she writes in bold letters “conservation of angular momentum”. Double underlined.>
Remember “conservation of angular momentum”? Picture Goldie swimming in a counterclockwise circle, not touching the glass. A funny circle with the axis of it parallel to the floor. To swim like that Goldie has to push water in the opposite direction. So the mass of water in the sphere is now rotating in the clockwise direction. More slowly than Goldie because it is more massive than Goldie. But the water touches the inside of the sphere and (because of viscous drag) starts the sphere rotating in the clockwise direction also. So, oddly enough, the sphere rotates in the opposite direction of Goldie’s motion. And when Goldie finally has enough of going backwards and stops, so does the sphere.
<Wiping chalk dust from her hands, Pluterday now retires, sure of victory...> |
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//Stuffy the oranda//
Used to have 4 oranda's - great fish. |
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// Goldfish bowling would be fun // |
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Not, I imagine, for the goldfish...... |
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<borrows [pluterday]'s mortar-board to use as a fish-sphere rest>
If the sphere were less than completely full, Goldie's exertions would theoretically (and imperceptibly) move the water; assume Goldie facing to your right - surface of water rotates clockwise so that right end is lower than left end. Effective centre of gravity of water is moved to the left. Sphere rotates anti-clockwise. However, said he, pointing significantly, if the sphere were full, no such change would occur in the centre of gravity, thus no rotation would occur. In fact, said he, having just thought of it, given that Goldie is neutrally bouyant, Goldie's mass moving to the right would counteract the water's mass moving to the left, no movement of C of G would occur and Goldie would swim round in circles, as usual.
<returns [pluterday]'s hat> |
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<taking yet more medication>
C of G! This is not statics, its dynamics! If you drop a spinning cue ball perpendicular on a pool table, it runs off, doesn't it? Even though the C of G is exactly over the point of contact? |
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I think that the motion would arise as a result of friction in the laminar flow region between the surface of the bowl and the moving fluid generated by the fish; the fish is expending energy to move, and momentum is conserved. But I don't believe any movement results as a result of moving the centre of gravity, since if the fish is neutrally buoyant in a competely filled sphere, the system is effectively isotropic. |
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I'm starting to wonder if the Coriolis force might have some bearing on this problem. And whether the globe can be considered truly hermetic, as gravity acts both inside and outside the phase boundary. |
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//How is dear little Goldie going to overcome the inertia of the system in which he/she is the only denizen?//
Friction, dear UnaBubba, friction. Picture a little man in the sphere. No water. The little man takes a step, the sphere rolls. That’s because C of G varies of course, and its a little different from the Goldie’s situation. But it is still friction with the ground that makes it possible to get going. Now take a gyro. Totally symmetric, with a C of G right in the volumetric center. Spin it up in your hand. The housing produces a torque on your hand, doesn’t it? If you were to lay it on the ground, it would roll away. The angular momentum is converted to linear momentum by fictional contact with the ground. In this case, Goldie is the rotor of the gyro, and the sphere is the housing.
<but she moves! mumbles Pluter as they take her away to the stake...> |
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What if the fish wanted to get across the floor so badly that it repeatedly swam at full force against the inside of the sphere, bashing its head against the glass again and again? |
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//This is not statics, its dynamics!//
Only after the bowl is moving. Until then, it's just a fish-sphere sitting on a desk (or in a hat). |
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Roll, roll, roll the bowl
Gently across the floors.
Merrily, merrily, merrily, merrily,
Now I'll explore the great outdoors. |
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[UnaBubba] Let’s say Goldie is in a bowl with 100 times her own mass in water. If she makes 1 circle per second (typical lazy goldfish is Goldie), the water must rotate on average once per hundred seconds in the opposite direction. This rotation is imparted to the bowl, which then takes a quite leisurely stroll around the house until it gets underfoot and is accidentally crushed. Goldie is dead, but the baker boys say no, no, impossible, Goldie cannot be dead, since she could never have moved to begin with. They are all quite clear on this. A vote is taken, and Goldie is resurrected. |
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Horizontal circles will simply cause the sphere to rotate on the spot. You need vertical circles to make it progress, but due to gyroscopic effects (as pointed out earlier) it will not move in a truly straight line. Not that there is such a thing as a truly straight line, due to the curvature of spacettime induced by gravity. Or rather, gravity is the name we apply to the observed effect of spacetime curvature caused by mass. Or something. Excuse me while I just go and bash my head agains the walls of this transparent sphere I seem to be trapped in. |
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<adjusts browser to report on first appearence of "Crash Test Goldfish" on 1/2B, starts taking bets on who will post it> |
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Good grief. If we can get road cones to move on their own, I don't see why a goldfish ball is such a problem! |
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It seems quite obvious. The ball won't move unless the displacement of water results in an imbalance. This won't happen as long as the fish is floating as it exactly counteracts the displacement of water. |
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If a male Betta can be specially trained to blow bubbles at a fast enough rate to exactly counteract the forward thrust of his tail, AND to sit dead centre of the sphere while he's performing these antics, then the resultant imbalance of water may just be enough to overcome the friction between the billiard-smooth sphere and the baize surface on which it rests. Perhaps. |
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Okay, here's the solution: |
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Fill the sphere to a level below one quarter full. Train (or genetically modify) the fish to jump out of the water in the desired direction of travel, landing on the dry inside surface of the sphere, beyond the edge of the water. Viola! A center of gravity imbalance has arisen, and the sphere will move to rebalance the center of gravity. The motion will re-submerge the fish, at which time the entire process can be repeated ad infinitum. |
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//It seems quite obvious. The ball won't move//
Try this then:
The Goldie
10 parts rum
1 part dear departed Goldie
(quick frozen in liquid nitrogen)
Now look. Does it spin? |
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[Bx] - no GM needed. Put one of those walking catfish in there. It keeps trying to get out of the water, but never quite succeeds. |
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I think this would probably work with snails. Just really slowly. |
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Fill the house with one meter of water. Add seals. Watch the fish bowl-ball move. |
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I like [notme]'s solution: motorize the bowl and drive it off sensors. Fish swims to this side, the bowl moves that way. This can also solve the oxygen problem too, as the motorized platform can contain a mini aerator as well. |
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You can make it fun for the fish, by making the robotic platform look like one of those battle robots from Robotech or MechWarrior. That way the fish can get its long-awaited revenge on your cat by chasing it around and scaring it! (WTAGIPBAN) |
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// You can make it fun for the fish // |
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So all fo a sudden, [krelnik] is the world's expert on what goldfish consider to be "fun". That raises somne intriguing possibilites, especially of he's writing from personal experience; either (1) [krelnik] can link telepathically with goldfish, or (2) [krelnik] is a goldfish that can operate a PC, or at least a web-aware PDA. |
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//Put one of those walking catfish in there. It keeps trying to get out of the water, but never quite succeeds// |
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Good idea lurch. One of my fish is a Plecotomus that frequently ‘suctions’ itself above the waterline. That would make one side of the sphere heavier. |
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Back in the day, I was pretty certain I wanted to be an aerodynamicist. Then I took fluid mechanics. It made my head swim. |
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I'm pretty certain that the Reynolds number here is pretty high, which means that the viscous forces related to a fish swimming through water are pretty negligible in comparison to the streamline inertial forces of displacing the water out of the way. As to what that means anymore, I have no idea. |
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Fish have a miniscule drag coefficient, which means that they don't need to expel very much power at all to move forwards. Because water is nearly incompressible, there is little pressure differential between nose and tail, and the only wake created is due to the frictional losses associated with maintaining a constant speed in a fluid, which are roughly proportional to its speed as long as the fish hasn't gone off on a caffeine binge. The wake created is for all practical purposes nonexistent, and the fish is largely 'slithering' through the water, creating as little 'dust' as a sidewinder would while crawling through the desert. |
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pluter's argument makes no sense at all. If there were anything to it, we'd all be driving fish powered cars. |
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Short of the fish getting out and pushing, the bowl ain't gonna move. |
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Dang, now I want to try an experiment. Motorized submarine or something to create a real current inside a glass jar. It just might do the trick. |
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waugs, don't forget that all 'internal force' vs. 'external force' boundary diagrams don't include internal energy generation as a factor. |
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what we need is a hamster in a wet suit with a tank of oxygen on his back. time events carefully though. |
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po dear, I'm laughing so hard I can barely see the keyboard. That annotation needs to be framed. |
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I think it's pretty well agreed by this point, that a globe full of water with a fish in it won't roll of it's own volition... we'll need some sort of sensory system to detect the fish's movements and respond with mechanical movement - a negative feedback system, maybye with water jets. Like: Goldy moves off-center, and water jets push him back automatically. The force needed to push Goldy back to the center of the sphere is translated into external movement through traditional means like motors and wheels. This isn't anywhere nearly as simple as just a goldfish ball, unfortunately... |
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I still think the cat will make this whole thing redundant. In more ways than one. |
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In what way sweetie? <dribbles> |
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I've got it - Octo-Balls. Ditch the fish entirely (but not literally, of course) and replace it with an octopus. Not only could they use their suckered tentacles to "walk" the ball around the floor, but they're a lot more interesting and exotic than goldfish anyway. Plus they change colour depending on their surroundings and their mood. Which would really freak the cat out. |
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"Where are you off to, dear?"
"Just taking the octopus for a walk, love." |
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(Wordgineer enters room, notices pluterday babling to herself in a corner, clearly insane by now) Goldie must move! If she can move water in one direction (which she must to propell herself forward), conservation of momentum states that if this water was to stop moving something else must turn - the sphere. The only arguement that has been made against this that makes any sense is that goldfish, by nature, wouldn't swim in upside-down circles. I argue Goldie wouldn't try to swim in an upside-down circle, but instead would collide with the side of the sphere. Thus she would still be imparting motion to the water without herself moving. |
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I propose the following experiment for doubters. Fill a tennis ball can with water. Give this tube to a friend, and have them walk up a hill. Set up a flat surface at the bottom of the hill. Have your friend roll the tube down to you, and quickly place it on the flat surface. When you let go, I'll bet you all of your fish that it will roll. |
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No, not the sphere. The fish itself moves in the opposite direction. |
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Right, but if you conceed that the water in the globe moves, then you must see that friction between the water and the globe will impart a tangential force on the globe. With nothing to counteract that force, the globe itself will move. |
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No, I don't see that at all. |
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(Worldgineer grabs mortarboard, wipes it off, and draws a free-body-diagram of a small piece of the sphere. This looks like a curved line, which is drawn in blue chalk. He then draws a red chalk arrow following that curve.) "This is the tangential frictional force. Any time you have water flowing past a surface, there is a fricitonal force." (waugs starts to speak, but is cut off) "There just is, otherwise boats could go as fast as they wanted. Now, " (hands the red chalk to waugs) "show me where an opposing force is. If you can't, then since Force = Mass * Acceleration, the thing will start to move." |
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What I don't see is how this even applies to the stated problem. Tangential frictional force has nothing to do with this issue. |
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We're talking about a fish inside a sphere full of water. The issue in question is: if the fish swims from the center of the sphere to one side, will the sphere roll in that direction? |
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The fish can swim around all it wants inside the sphere, moving the water any way it pleases. But it is still all contained inside the sphere. The combined weight of the fish and the water, and the pressure it applies to the inside surface of the sphere, will not change. Therefore the sphere will not move. |
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If it were so, then why haven't goldfish been knocking their bowls over all these years? |
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I find it quite amazing how many of you aren't getting this. |
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1. You're avoiding the question. Tangential frictional force has everything to do with the question. Please draw your force arrow. |
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2. That is not the issue in question. The question is can the fish move the sphere? I agree that if all the fish does is swim from the center to the edge, that may not move it at all. However, if the fish keeps swimming after she hits the side, moving the water in a circular manner, she will move the sphere. |
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3. I agree with the third sentence of the third paragraph in your arguement. However, you jump to a conclusion in the fourth sentence that I do not agree with. |
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4. Because bowls aren't spheres. |
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5. My sentiments exactly. |
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I'm not avoiding any question. As I said, I do not agree that tangential friction has anything to do with this problem. |
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I've clearly made my point. Argue with someone else. |
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Why do you say that tangential friction doesn't have anything to do with this problem? You have not made your point. |
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[pluterday}'s right. Fish and water don't have the same density. Replace the goldfish with a fish of drastically lower density, say, a fully inflated blowfish that takes up about a third of the volume. This would be similar to having a 2/3-full sphere of water, but with the air pocket able to move from side to side or top to bottom. |
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If the fish manages to create a current and maintain it, then he will move the sphere. But one short burst forwards will not do it. |
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The fish will eventually have to swim in vertical circles in order to keep moving, but not as soon as you might think.
Given that he is either above or below a horizontal axis through the center of the sphere. If he's above it and facing to the left as seen from the side, then as he swims forward, he'll create a totally miniscule current clockwise, and vice-versa if below. |
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Now, he continues swimming to the left. Provided that the bowl is sufficiently large that he doesn't immediately hit the edge, he will eventually have to swim against part of the current that he himself has created. However, since some of that current has been tapped off due to friction at the water / bowl interface, (thus powering the rolling of the ball), he'll still move forward, relative to the ball, if he continues at the same level of effort. And so he must turn some other direction, or simply pause 'til the current carries him back to the opposite side. |
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I think it's about time for a swimming-fish clock. |
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Provided that the force is large enough, (which I seriously doubt), my view is that there are no fundamental engineering mechanics reasons why the bowl would not move. However, I doubt that there would ever be enough current to get the ball rolling, even with a hundred fish. |
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The pufferfish fills itself with water in order to puff, and so that has nothing to do with its density. Where would it suddenly acquire a large source of gas? |
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bliss - I think we're debating it purely because it is a cute idea and as halfbakers would like to find a way to get it to work. |
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waugs - I'm sorry if you thought I was arguing - I was just trying to convey my point and let you know that I don't understand yours. |
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Thank you Ray, I was going for a visual to hopefully demonstrate inner movement can cause outer movement. Perhaps my magic 8 ball would have been more effective.
(And I highly recommend not going to blowfish.com for verification.) |
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//Fish and water don't have the same density.//
Of course they do. If the fish were more dense, it would sink; if it were less dense, it would float to the surface. I know that fish can control their bouyancy by muscular control of the swim bladder, but when they are just swimming around, fish and water have the same density. |
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//fish and water have the same density.// |
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Net, they have. However, this density is not uniformly distributed. Spin a fishbowl at 75,000 RPM for two minutes and you'll observe: |
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Some fish at top (may be bubbles). Some fish at bottom. Water in the middle. |
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Shirley this depends on how fast the bowl is accelerated from rest to maximum - or are you considering the massive "tidal" forces due to the steep centripetal force gradient though the medium ? |
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//not uniformly distributed//
Do you mean that the density of the fish is not uniformly distributed within the fish, or that density is not uniformly distributed within the fish / water system? If the first, I know but it's irrelevant to the current discussion; if the second, it is - the fish and the water have the same density, so distribution *must* be uniform. |
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[Dimandja]: You even quote from your link: "a fish fills its bladder to the point at which it displaces a volume of water that weighs what the fish weighs." That means that the fish and the water have the same density. This only changes when the fish is moving higher or lower in the water. Once it is at its required depth, it manipulates its swim bladder so that it, again, has the same density as the water. |
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Well, I think you're *all* right. Every one of you. |
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Viola! Shark Feeding Frenzy Bowl! |
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[Dimandja], have you been assuming all along that the fish would impart movement to the sphere simply by bashing into the sides? |
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magic eight ball experiment---I swirl it, set it down gently, it begins to move around. (for those unfamiliar, a magic eight ball is a sphere filled with water and a die-like cube with different sayings on it, a little window on the bottom of the sphere allows you to see one message at a time. Currently in says, "outlook not so good") |
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I should think this problem is similar to, and maybe easier to visualize with, a bird in an air-filled sphere. Some questions that could be asked as the bird flies from left to right causing an air current from right to left:
1. The air current would cause an initial force to the left on the sphere, but would it equal the force of the bird as it collides with the right wall?
2. Would the sphere sway left and then right?
3. The air current would swirl around and produce a lesser force on the right wall (+ for the bird) and then even produce a slight headwind for the bird (-) slowing its progress?
4. Though this is a closed system with no friction against outside air and floor, and ignoring production of CO2 and heat, should the bird's potential energy in its muscles be considered?
5. Would the result be different between a gentle, increasing push and an impulse after getting up speed? |
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Other questions that may be of interest:
6. Is the sphere system lighter when the bird is no longer standing on the bottom?
7. Can a strong bird lift the sphere by flapping hard enough with its back against the top?
8. Why is the answer to the last question different than / the same as pushing the sphere forward? |
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For some time now, this conversation has resembled one I heard somewhere about the load-bearing capacities of English vs. African swallows. |
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So the key is using African goldfish? |
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anyway, throughout all this, i can't believe nobody has correlated this idea to an even more awesome idea: (...which a friend of mine once mentioned, but, as it applies in this situation, here it is. i take no credit.) like [lurch] and [notme] had mentioned, use optical sensors on the bowl--when the fish moves in a certain direction, the bowl moves with it. but here's the kicker: i'm not talking on the ground, i'm talking IN THE AIR! that's right, a sealed goldfish bowl suspended from a miniature helium balloon that has miniature fans attached. the fans get their data from the optical sensors and turn on/off accordingly. now the fish has 360 DEGREE range of motion! it's swimming through OUR world, instead of just its own. the interesting thing will be: does the fish learn how its motions translate in the real world and alter them accordingly to move among us? or does it just randomly float around and bump into stuff since it only has a tiny fish brain? i would love to see this tested someday. |
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p.s. this wouldn't really work inside... unless you were in some sort of arena or auditorium. |
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Nice work, squidink! I was close to posting a "Goldfish Bowl Newton's Cradle" idea just to muddy the waters still further on the physics of this debate (and perhaps drown it out entirely with the sounds of breaking glass), but you've restored my will to live. |
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"Why are you crying, Timmy?" |
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"No. I left the window open.." |
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To paraphrase from a classic Carlin routine: |
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"Mom, I lost my goldfish!"
"Well where did you have it last?"
"Hey, if I knew that, I'd still have my goldfish."
"Well it didn't just get up and walk away!"
"Hey, Mom, I think you figured this one out." |
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I thought through the same analogy with a plane. However, the model is complicated by the bird / plane's much larger net density compared to the air it displaces. This is significant because the problem no longer becomes one of an equivalence in net density displacement between fish and water, but primarily of an internal conservation of momentum of the entire bowl, given a displacement in mass that the goldfish model doesn't see, because of the water's sameness in weight as the net fish. (fish net?) |
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An impulse for a bird is more likely to get the air bowl rolling, however, it will not stay rolling. Impulses are almost always more effective at overcoming static friction than the same energy spread over more time. |
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A second difficulty arises when you compare the difference in Reynolds numbers between air and water, and so the simplified models would use different factors, effectively making a comparison tough to work out. |
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The bird / air bowl problem is in some way functionally equivalent to the explosion of a non-propelled firecracker, in that the directional momentum of every chunk of mass involved in the system must be maintained. Pieces fly off in random directions with seemingly random velocities, but if you add them all up vectorially, the net directional change is 0. |
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Hence, if the ball is stationary and the bird starts flying to the left, yes, the ball will counteract by moving right. If we discount frictional differences of impulse vs. steady force, when the bird hits the wall, the whole system will come back to its original starting point, and probably a little past because of impulse and frictional effects. |
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The bird will never be able to lift the bowl by flapping its wings, if the bowl is sealed. That's me trying to lift myself up by my own hair. |
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Also note that a sealed bowl is mechanically different than an open bowl with fresh, stagnant air sources, which may complicate my whole analysis here. In the sealed bowl, a cyclone of some sort will be created, which may, like the fish problem, create its own effects, one of which would be to instantly ground the flight of the bird, as the air which he's flying against is being replaced by air that is directionally unfavorable to his lift. He's like a Harrier that's sucking in it's own exhaust and crashlands.
The only way he'll get off the ground and stay there would be to be inside a ball that is large enough such that a steady-state current is never created throughout the system. |
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Summarizing per FJ's numbers: |
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1. Sortof. They would be mathematically equivalent. However, the larger impulse wins out at the beginning due to the percentage of force lost to overcoming static friction. |
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2. Yes. conservation of momentum of the system would dictate that it landed where it started. |
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3. The bird won't be able to maintain lift for very long, due to an induced downdraft. |
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4. No. It's functionally equivalent to the firecracker problem. |
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5. After getting up to speed, a gentle, increasing push is favorable over an equivalent impulse, due to non-rigid body energy losses. |
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8. It's nearly the same. The difference lies in the fact that in the horizontal direction, we've taken it as a given that the bird is suspended by some magic. If a bird jumps off of the bowl bottom (which is in contact with the ground, obviously), and rams himself into the top, then the bird has something to push against which is outside the system, and the bowl will jump up as a result of his impulse. However, the bird will not be able to lift the bowl by flying upwards, as he won't be able to fly at all, and if he did, then the force of his downdraft against the bottom of the bowl is exactly the same as his push against the top. Similarly, a fish cannot push a ball by forcing himself against the edge, since he's pushing back on the water to do it. |
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But the bird model is not quite the same as the fish model, for the reasons I've described above. Fluid dynamics problems usually need to be taken one at a time and are rarely transferrable between one system and another, as the math models used to solve the system will be highly dependent upon the properties of the fluids involved, the speeds involved, the pressures, etc, which is why we have weird mathematical things like Reynolds numbers, Mach numbers, Cauchy numbers, etc. We first find a few of those 'dimensionless numbers,' and then decide what type of aero-dynamic model fits the scenario based upon the numbers generated by the first go. |
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[The only way he'll get off the ground and stay there would be to be inside a ball that is large enough such that a steady-state current is never created throughout the system.] Woot! You solved that problem. So the bird could create a cyclone that would not directly be effecting the air directly around it. So we could also say that a sealed ball the size of a SUV, holding say, a mako shark (I hate goldfish), would be moving from the sharks own movements. Now, as said with the gyroscopic movements, if the shark did only swim counterwise or clockwise (1 direction only), due to a gyroscope not rolling in a straight line, the shark would eventually have the ball tilting (as it will start to spin from circular in its own space, to diagonaly), and after a few rotations diagonaly, would start to roll in a very random path. Now brings up the questions of "If a glass sphere on a frictionless surface starts to roll, where does it go?" |
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<roby scratches head and wonders what all the fuss is about. Shirley this is obvious?>
Dimandja's link shows possible answer. Goldie starts at the bottom of the bowl on front side, floating with neutral density, (Goldie mass is 100 g, currently displacing 100 g of water with 100 cc of volume).
Goldie spots shiny mirror outside of sphere. "Let's get a closer look," he/she might think, if it could.
Goldie swims to back bottom side of sphere, expands bladder to increase volume to 200 cc, displacing 200 g of water, though Goldie mass now more like 101 g (original 100g plus a gram for the extra air). Goldie rises, ends up at top back end of sphere. The now displaced 200 g of water redistributes it elf in sphere, changing sphere center of gravity, initiating forward motion. From top back of sphere, a bloated 200 cc Goldie maneuvers to top middle, thereby shifting half the water mass back the other way again, to slow but not stop forward momentum. Goldie then normalizes volume to 100 cc,. swims to front top, then releases air in bladder, reducing Goldie volume to 90cc, thus reducing water displaced to 90 cc and 90 grams, causing 100 g Goldie to sink down to bottom front of sphere. Water in sphere redistributes it elf again, extra mass to front of sphere, changing C of G again, continuing sphere's movement forward. 90 cc Goldie manuevers from bottom front to bottom middle, shifting C of G back again buy by half as much, then normalizes Goldie volume to 100 cc again, swims to back bottom, prepares to reinflate to 200 CC again, and so on until Goldie is close enough to see him/her elf in mirror!
Now, I'm sure my numbers are gross exaggerations of the density changes Goldie is capable of making to rise and sink him/her elf in water. But I think it shows that Goldie could initiate and control change in sphere C of G and thus sphere movement. |
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//Do you mean that the density of the fish is not uniformly distributed within the fish// |
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Yes. Bones, and other structures are denser. Swim bladder is lighter. Net, the fish is able to trim to neutral bouyancy (this works with scuba divers too, but the centrifuge would be too big). |
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I used to operate a centrifuge for separating cellular components. If a (homogenised admitedly) liver cell will separate under these forces, goldie will probably too. You'll be left with fishy bones crumpled at the bottom of the tank, covered in a layer of fishy muscle bits, clear-ish water in the middle and fats and bladder bubbles on the surface. |
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Speed of spin-up is not important. It's the forces at peak speed that do the separating. |
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That reminds me... perhaps we could use one of those magnetic beaker stirrers on a low setting to give Goldie a gentle spin. |
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//Need to add plenty of slime coating to prevent injury to the fish.// |
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Thunbwax, what kind of mucus covering do you propose. I've thought of silicone, but I'm concerned it might dissolve and/or poison Goldie. |
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There's nothing to sphere but sphere itself. |
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// Woot! You solved that problem. // |
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No, I did the opposite. I killed the air model. The induced current is what we were relying on to propel the ball in the first place. |
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// Goldie swims to back bottom side of sphere, expands bladder to increase volume to 200 cc, displacing 200 g of water, though Goldie mass now more like 101 g (original 100g plus a gram for the extra air). // |
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roby got as close as anybody could, however, there's another problem. |
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Where did the displaced water go? If we're assuming that the sphere is closed and water-filled, (which was what I was working on), then Goldie will never expand against the pressure-sealed system. And if the sphere is not completely filled with water, then Goldie must effectually pressurize the air above, which is still tough to do. |
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If the bowl is only half-filled, then what if the fish jumps out of the water, hits the side of the bowl, and splashes back in against the edge? Hmmm... gonna have to think on that one. |
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Schrodinger's fish... paint one half of the outside of the sphere black. Upon swimming to the visible side, the fish may collapse into wave form, causing instant system depressurization and a temporary vacuum in the water. The ball then rolls towards the invisible side... |
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Dimand, once you fill the tire with water, you destroy any chance of rolling the thing, because of the displacement problem. The only way it works is if you're not neutrally buoyant, like walking along the surface, perhaps. |
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RS is right. Bladder/density adjustment propulsion would require ability for sphere to accommodate changes to overall water volume.
I wonder if sphere itself had minor elasticity?
Or the volume of air that would be compressed would have to be many multiples of the incremental volume Goldie could increase his/her elf.
(i.e. Goldie could probably compress air volume from 1000 cc to 900 cc, but not 101 cc to 1 cc.)
And if there's a substantial air pocket, air bloated Goldie will be engaged in a frenzy of fin flapping to keep head under water (otherwise bobbing Goldie not displacing water). |
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Yeah, I suppose it is a question of the numbers. |
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You could make a semi-elastic spherical container, suspended somehow inside a rigid glass sphere with a little pinhole in it to balance the pressure of expansion. |
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Goldie could have psycho-kinetic powers? |
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RS unlocks another great alternative for propulsion: Big Fat Black Fish convection method!
Requires high ambient light energy, fish hue capable of transferring light to heat (Black fish), and sphere materials to conduct heat quickly away from fish-heated water to surrounding air, thus temporarily creating air pressure differential on one side of spehere.
Would work for the floating in air version of the sphere, or a REALLY low friction version of the ground sphere, where changes in air pressure would be enough to get sphere rolling.
Black Fish flattens it elf against side of sphere, absorbs light, heats up, heats up surrounding water, conducted through sphere to adjacent outside air...higher air pressure on one side starts sphere rolling in direction of lower air pressure...voila!
But alas, the problem is then semantical. We no longer have Goldie doing the work. |
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Maybe Goldie should test fly the clear, spherical rocket. |
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[stormo] My jaw dropped when I saw your link. It amazes me what is baked in this world - about everything. |
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OK. The sphere doesn't end up on the sidewalk - possibly with three dead fish.
Now you tell me fish can't fly. |
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That stormo link is great. I want to see it extended to Betta-controlled fighting mechs. |
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So if all the fish in the ocean simultaneously decided to swim in an easterly direction, would the Earth stop rotating? |
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Maybe tidal waves on east coasts. Fish, the sea butterflies of chaos theory. |
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//So if all the fish in the ocean simultaneously decided to swim in an easterly direction, would the Earth stop rotating?//
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Yes, that's what really happened to the dinosaurs. |
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Help! I've unleashed a monster! Steven Spielberg would be proud. I'll never venture into the water again without thinking about fluid dynamics and neutral bouyancy and suchlike: oh, for those halcyon days before I encountered the halfbakery, and swimming was just a simple pleasure... |
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If you'll forgive the mixing of metaphors, this seems to have turned out to be an idea with legs. I remain as ignorant about the laws of physics as I was when I first posted the original idea, but still - there's one simple fact I can't disagree with. Given that Goldie is encased within a perfectly spherical ball, and that he's only resting on the floor with the smallest possible amount of bowlage (fractions of millimetres at best), I find it hard to believe that Goldie's frolicking won't move the bowl at all. Theoretically at least, Goldie starts out at a point of perfect equilibrium - so surely (even given my ignorance of the more obscure laws of physics) any movement he makes must have some kind of effect on the dynamics of his bowl as a whole? |
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His excertions can't just dissapate into thin air. They must have some kind of effect. |
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Okay, forget the water for a second. Let's say, hypothetically, that Goldie is swimming, or trying to, in syrup, and is, in this example, neutrally buoyant and unsupported by an external lifting or lowering force. |
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Goldie wants to go forward, so (he / she / it?) pushes backwards on the syrup. The jello now pushes against the glass on the far back wall. Goldie moves forward. A goldie-shaped vacuum is now created, which is then filled by a weight equal to his own. Which means, goldie-shaped syrup moves backwards in precisely the same amount, counteracting goldie's mass. The ball sees no net displacement change in mass, and no generated rolling force. |
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Eventually, the syrup wake pushes on the far back wall before circulating around, which is obviously attached to the front wall as well. The front wall pushes on the syrup in front of goldie, and goldie has now created a current, against which he can create no headway at any constant force. Only by accelerating before the current comes back to get him can he move forward at all. |
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Can't we just propell Goldie around on a wave of wishful thinking? |
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Ray, we've gone over this before - sans syrup. Now imagine Goldie swimming in her syrup near the bottom of the sphere. The syrup pushes not just at the back of the sphere, but tangentially (around the circle) at other syrup. Goldie-vaccum is created behind Goldie, replaced with syrup in front of Goldie. Overall there has been rotational momentum created in the syrup, balanced nicely by the rotational momentum created in Goldie in the opposite direction. Now, although Goldie keeps going, the syrup tends to stick to the wall of the sphere. Now, there is more rotational momentum in Goldie than they syrup. Where does the rest go? To rolling the ball. Sure, Goldie will end up having to do loops - but my point is that the ball will roll. |
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[Worldgineer] Might as well stop trying to convince them. After all, we know we are right. Back in the old country, before democracy, we could have simply shot these people, but now they have a right to be as wrong as they please. <sigh> But on the other hand, the more they rail against roaming Goldie, the more votes for [lostdog]. |
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Thanks, pluterday. I'll try and make sure that you're last against the wall, come the revolution. |
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Teach a man to to fish, and he'll eat for a day - teach the fish to run away, and we're talking a whole new world order... |
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World, I understand the whole tangential fluid vortex argument. |
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You get the impression that I'm railing? No no no... I'm exploring. Thinking it out as I type, for the challenge of it. |
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Don't forget that the syrup / water / whatever is also sticking to Goldie and slowing her down. And remember what I said earlier about fish and wakes. Essentially there is very little rearward water displacement created. Some of the water surrounding Goldie travels forward with her, and most of the wake is simply lateral displacement. It's more like slithering through the water than motoring through it. |
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Any boat that creates a large rearward disturbance in the water is simply not that hydrodynamic, because the energy losses involved in displacing water are exactly balanced by the friction, volume displacement efforts, and small pressure differential of advancing forwards, given a constant speed. Wakes are a detriment to speed, not an advantage. |
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Bowl no move.
Goldie is a fishy Sisyphus.
Push and push but go nowhere. Die trying. |
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I have been mulling this over since it was posted, and think that the law, for every action there is an opposite and equal reaction, pretty much sums it up.
It would be just too cool to have a roaming goldfish bowl, but for every wave that goldie makes, there will be an opposing wake.
I think that if there was an air gap this might change, much the same way that you can spin on a swivel bar stool in jerks, or get a swing swinging from a still start, but as long as the bowl is completely filled with water, Goldie go nowhere quick. |
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If the fish was heavier than water, it could move the bowl by slowly creeping forwards and then jumping back. (Try this on a chair by leaning forwards slowly then jerking back; you are heavier than air.) |
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When the fish moves horizontally, there is a slight change in the overall momentum of the ball, since the momentum of the fish is always greater than the momentum of the water it displaces. However, if friction is high enough and the momentum small enough, the ball will not move relative to the ground and the momentum will be transferred to the whole ball-earth system. |
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Thus, moving forwards slowly, the force it exerted would be too low to overcome friction, but when it jumped back, the sudden movement at high speed may be able to overcome friction and launch the ball (free of the floor) in the opposite direction to conserve momentum. This is analogous to moving a bar stool or boat or whatever by a quick jerk. |
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If the fish is homogenous and has the same density as water, it's stuck. If there's insufficient friction between the ball and the floor, it could only move if the density within the sphere was unevenly distributed. |
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[Ray] Goldie's surface area is much smaller than the sphere's, therefore syrup sticks less to Goldie and the ball rolls. As for the dynamics of a slithering fish - they are unimportant here (a red herring if you must ;-). Goldie has to move some amount of syrup in the backward direction or she couldn't move. |
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Let's take a step back and look at the sphere. The sphere doesn't know anything about goldfish, doesn't know about fluid dynamics, it just knows it's resting on a nice flat smooth surface and it's touching syrup on the inside. Then, the sphere feels that the syrup is moving - it's moving in a circular direction that's pulling the sphere to move. Since the only force the sphere can feel (other than gravity and the floor, which cancel each other out) is this tangential force coming from the syrup, it must roll. |
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I think we might be able to use the energy expended in this thread of discussion to propel a couple of hundred goldfish bowls around. |
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uuuuummm yeah. and what about the breathing? |
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See [link] for clear explanation. |
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[Worldgineer] and [pluterday] are right -- any movement in the bowl (goldie) will have impart a force on the water, which will in turn impart a force of the surface of the fish bowl. This force will then be translated out of the system. Wether or not this force will be great enough to move the bowl will depend solely on the friction holding the fish bowl in place.
Also every is make a wrong assuption to begin with -- fish are *not* neutrally bouyant. Has no one every see a dead fish float to the surface of the water?? Fish must be lighter then the water or else this would not happen. |
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Imagine the fish butting against a point inside the fishbowl, so it can't move, then swimming in such a way that it propels the water tangentially. It will soon create a kinda "whirpool". That and the friction will cause the water surface to change from the horizontal plan it has when calm, changing the sphere cdg and, if we eliminate friction completely, moving it. It will not work if the sphere is completely water filled, all forces cancel, as everybody plainly sees.
Brodie, dead and decomposing fish are lighter than
water; living fishes are usually neutral (fishes can change buoyancy between limits).
So there.
that |
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There's something lacking, the whirpool axis has to be horizontal, an vertically-axed (how was that?) whirpool wouldn't change the center of gravity projection on an horizontal plane, and being the friction resultant located on this plane and the ground reaction to the fishbowl perpendicular to it, nothing done.
Very deep down I don't really know the least about what I'm saying, but it sounds pretty impressive. |
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But, if the fish farts... |
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Simply had to bring this one back up after the crash. |
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Even if the fish can't move itself, it'll be fun for my cat to play with. |
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What if there were two fish? |
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What if there was a red fish, blue fish? |
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Well, there goes SCABA, the Self Contained, Above Water, Breathing Apparatus. |
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The mechanism I would propose is a 4 by 4 toy truck chassis for an aquarium bowl and a camera sensor that translates fish's movements to movements of the truck |
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(zeno respectfully enters the room carrying an egg. He asks if anybody can tell him wether it is a cooked egg or a raw egg. Wordgineer sets it spinning. Pluterday stops it abruptly and and lets go. The egg resumes spinning of its own accord. They triumphantly anounce in chorus: It is a raw egg!) |
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The friction of the water on the inside of the bowl wil make it move across the floor but only very little. The tiniest flake of dust will be an unpassable barrier. |
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However, if the fish would swim well below the equator of the bowl, with its nose to the glass, it would be able to *nuzzle* itself around the room with ease. Pushing against the glass side which curves up would make the fish go up but it could withstand that and keep itself down where it is. The bowl will move. |
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Now put two small bowls on the floor with a japanese fighting fish in each. Now ask your friends to come visit. |
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I think that the people who say it can't move are assuming that the bowl is filled completely with water, and the people who say it can move are assuming there is some (compressable) gas in there. |
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If the bowl was COMPLETELY filled with water, and perfectly rigid, would the fish even be able to move its fins? |
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I'm sorry. Its linoleum or nothing. I still don't think it will work. |
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i think this definitely WOULD work - it might not be pretty, but it would work. the ball would roll somewhat erratically, admittedly, and the fish would probably be swirling around in dizzy circles rather than happily nuzzling the forward wall of his rolling tank. there's also the problem of the fish getting air, but goldfish seem to be able to cope fairly well in low-oxygen environments, so they're probably the likely candidates. overall i'd say this would spell the end of a beloved pet - so maybe, in this case, sneak off to the petstore, buy an expendable goldfish, name it "test subject #001", and send it for a roll. observe results, improve fishball, flush mr. 001 and dodge fish rights activists. repeat. |
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Well robinism I think if the bowl is competely filled and rigid as you call it the water would have to be frozen. So the fish can't move. But is it hust filled completely the fish would have no trouble moving. If the water is put in under great pressure the fish might die but then we would simply not put it in in the first place and use a fish that lives in deep sea. It wouls survive and be able to move. |
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Again I feel compelled to state that if the fish swims below the eqautor with nose to glass it could nuzzle around the room with relative ease. |
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[zeno], that depends on if the fish can actually apply any pressure differential to the glass. Don't forget that to propel himself forward, he's pushing backwards against water. Also don't forget that he weighs no more than the water that surrounds him, and so the inertia of a speeding fish towards a glass barrier underwater nets to zero, as he must displace an equal weight of water rearwards. Furthermore, he is internal to the stable and inert system. In your egg-sample, the egg is set spinning by a force outside of it's 'system.' If you could 'stir' the water with your hand, yes, the ball would roll. But as the fish has no inertial reference frame, (not a leg on which to stand, in other words), as he stirs the water, the water stirs him. |
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[zeno], I meant if the bowl were completely filled with water (no air) and the WALLS were rigid (not the water). |
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[RS] Since you seem to agree that the fish would be able to stir the water, let's have her stir the water by doing loops about a horizontal axis. Now, instead of a fish and water let's imagine a solid ball inside another ball, connected only by a rubber band at two horizontal points. Wind up inner ball, close up your system, and set it down. As the inner ball unwinds, the whole system will roll. All we're really doing is replacing the energy storage in a rubber band with energy stored in a fish. |
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[UB] Of course, any motion will only happen assuming a smooth ball on a smooth surface. Any resultant non-vertical force in such a system will roll the ball. |
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Well, it IS a fantastic idea, one which reminds me just why I like the halfbakery. One suggestion, could you add a lava lamp feature, without the heat would be best, then I think it would be almost perfect. Also, a turtle could be added, for legwork. |
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Steel, Not a leg to stand on**. Made me smile, nice. |
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Robinism, Sorry misunderstood you there. |
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World, Good thought experiment there. But I think we all agree that the movement of water inside the bowl is either not strong enough to move the bowl or not strong enough to move the bowl spectacularly.
After all we want this fish to compete with the hare, not the turtle. |
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Imagine the fish outside the bowl in his scaba gear. Naturally he has a high-tech jetpack wich enables him to move in air as he would in water, up, down, sideways, the threedimensional works. (by now we have one happy fish who's wondering if scaba gear works in outer space and if there might be fishoids on other worlds) |
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The fish moves to the bowl at point x ( a point below the equator but not so low the fish would get stuck between bowl and ground.) It bumps into the bowl at speed y ( being a speed fast enough to move the bowl but slow enough not to damage the scabagear or hurt his nose) The bowl moves. The fish repeats this over and over again and once the bowl is moving a little he can start pushing continuously rather than bumping it. |
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So I have now taken the fish outside the system. Force is applied to the bowl from outside and it is obvious it moves provided the force is strong enough. If the force is not strong enough you can simply take a stronger fish or boost up the scabagear. |
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Now, the fish is back in the bowl. It sets of at a good trot (speed y) and aims for point x only from the inside. In the water it has to work harder to reach speed y but it can because we have a strong fish. It bumps against the bowl at point x with exactly the same force as the first time and exactly as much energy is transferred to the bowl, only now from the opposite side. The bowl will move. |
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It does not matter if the fish is inside the same system it wants to move. The laws of inertia make the bowl move for as long as the fish swims. we're not talking perpetual motion here. |
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Also this discussion reminds me of a discussion long ago and finally some russian guy (to lazy to google it) proved beyond doubt that rockets will move in outer space. It seems obvious to us now but way back when
people wondered: yes but the rocket has nothing to push against! |
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<as he must displace an equal weight of water rearwards> by Steel, it simply means turmoil. Fish can still bump as hard as it wants in to glass. Smack bang, inertia, movement. |
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Imagine ( yes I have thought of another thougth experiment I can not let it go) you are standing at the back of a small rowboat. You start walking towards the front and slowly accelerate. The last bit you take a small jump and stop abruptly on the bow. This way you can go across the lake. |
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Do you agree this can be done? Do you agree it is the same priciple? |
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In order to make this work, you could have Dale Chihuly make a special fish globe with several curly handles protruding into the inside of the globe. Goldie could grab onto a handle as he swims, so he won't just be pushing against water. Then you could get a whole school of goldfish in there, and teach them how to push in unison, each fish stationed at his own handle, like a crew team. |
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Also, the fish is not condemned to neutral buoyancy. (I recently learned a lot about buoyancy). The fish can use its gills to blow off the gas in the swim bladder, to make himself heavy. Then he could roll himself along the bottom of the globe, just as I would do if I were in a big glass globe. |
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<Blow off gas to make himself heavy>, exactly what I mean Robinism. The fish can choose its altitude inside the sphere and then applie force to whichever point it wants. It's elementary Watson, the fishbowl moves. |
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Note that I never said that the bowl couldn't go anywhere. |
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Being essentially incompressible, water behaves much differently than air. |
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The fish jetpack won't be able to maintain any flight inside a closed glass globe. He will be sucking in his own downdraft, and that is the cunundrum which the waterborn fish experiences, only to the larger effect, after a period of time. What this comes down to though is trying to take advantage of an impusle over friction as opposed to a longer steady stream of force the other direction. The bowl will roll if the fish can achieve a sufficient impulse, just like in your boat experiment. |
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Thanks for thinking on these same lines here Steel, Damn I want to do a practical experiment, I'm losing sleep over this, just love the concept. |
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I remember way back we had these little divers action figures you could wind up, mmmm... |
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The Roberts, the other day I saw the mythbusters on discovery and guess what. They proved a goldfish does have a pretty good memory. It can remember that the food is more likely to be found at the orange place then at the other place, even the next day. |
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The fish in my office knows that he gets fed at one particular corner of the fishtank. If you put food elsewhere, he'll starve. |
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EDIT: By the way, I'm thisclose to actually buying a goldfish, a clear hamster ball, and some good sealant. |
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Lovely principle, but you should probably know that the traditional round goldfish bowls one sees in fairs has recently been made illegal in Rome (the city, not the Papacy), due to concerns for CTG (cruelty to goldfish) (it is reported to make them go blind, due to lack of oxygen, and boredom). They also made it mandatory for all dog owners to take their dogs for a walk regularly, and provided official recognition for the nice people who feed the stray cats. |
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I just saw a special regarding the blood-sports of ancient Rome. I guess the pendulum swings slow but wide over there. |
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I really respect the physics expertise demonstrated by all of you here. But you are severely underestimating Goldie - and that is a mistake.
What would you do if you found yourself in a glass sphere half filled with water? Would you be able to find a way to move about? Sure you would. Simply by walking. Now you say, but Goldie can't walk he/she is a fish. But don't underestimate Goldie, just because his/her legs are missing doesn't mean that it can't compensate by his/her brains. A fish can control it's displacement - by submerging to the bottom of the bowl (but slightly forward) it will exert force on to the bottom-forward causing the bowl to move forward. ... gravity is the answer. (yes - technically this is not swimming, but any goldfish reading these annotations is tearing out his/her fins on it's head screaming - it's obvious! ... so I just had to throw this in) |
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Okay. So there's no chance of anyone getting this far, but this is a full and complete physical analysis. If there are objections I would be glad to
clarify and refine the model to illustrate. |
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____
Abstract; Bowl impractical, motion not impossible.
---- |
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I like the above, [ixnaum]. Just think of what you would do. I'd ram myself against the wall after slowly accelerating. This would jerk the ball forward. |
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I'm going to use a series of approximations to prove this. |
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Okay, so lets assume the fish is -exactly- and uniformly the density of water.
Hamster balls move because there's an imbalance of gravitational and 'normal' forces, producing a torque and therefore a rotation. (Normal force- you stand on stone, stone pushes on you to keep you up. Always 'normal' = 'perpendicular' to the surface. Same deal with hamster.) This route is unavailable to the fish. |
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So, to the approximations.
First of all, forget the water, and the friction. The fish is now a ball-gun. |
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It floats and fires blue spheres of kinetic energy. |
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Fish swims forward, by firing a ball backward. They separate at a constant rate. Then, the fish allows friction to brake it, firing another ball forward. |
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Timeline:
The backward ball strikes the glass bowl. The bowl accelerates backwards.
The fish stops.
The forward ball strikes the glass bowl, cancelling the backward ball, and the bowl stops. |
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Conclusion: Motion. But, only a jitter. I have no goldies to observe, but I'm told they move more or less randomly. The motion will be cancelled as soon as the randomly moving fish moves back.
You can test this yourself on a rocking chair. Jerk forward, then back. Or use a bike. Or water; jerk your arms forward, then back. |
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Now, let's discover that to actually move, the fish -must- take advantage of friction.
First, the fish accelerates slowly, firing many small balls backwards. As each strike the bowl, they are overcome by friction.
The fish, now going a decent clip, stops, firing a large ball forward. This strikes the bowl and is only slightly diminished by friction. Alternately it can strike the glass wall directly. Assume a metal-nosed fish-gun thing, so
it can't hurt itself. |
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The bowl-fish system now has a net forward speed. |
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If the bowl suddenly becomes frictionless, it will roll forever, otherwise it will come to a stop, but at a significant distance. |
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(Notably, the dynamic friction of surfaces moving is much lower than the static friction of motionless surfaces.)
I use this technique to playfully inch my bike forward. It has nothing to do with relative masses and everything to do with frictional losses. |
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Now, let's consider rotations, and add back the fluid in the form of balls going in various directions. |
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The fish, because an alien firm bought all its brain-stock, is swimming in a circle at a constant rate.
This supplies a constant rate of balls to the bowl wall, and a second (equal
in sum) stream of balls forward from friction, but in all directions with
wierd vorticies and such.
(If the forward and backward balls did not add up, then the fish would be accelerating, not constant.)
These forward vorticies eat energy, converting it to heat.
The backward balls provide force to the globe. It rotates. The constant thrust overcomes constant earthly friction, and the steady state is counter-rotation.
As soon as the fish stops, the bowl stops. |
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Regarding the fluid rushing around the fish as it swims, this is a zero-sum
motion as water is accelerated at the front of the fish but then abruptly declerated at the back as it hits motionless water. If this has an effect, it can probably be neglected. |
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So, the ball -could- be spun but this is unlikely. More likely is that friction would allow energy in the fish, fat and the like, to be converted into motion of the ball.
My intuition tells me that a low-friction surface would work best, amplifying any motion attained. So put it on a polished marble table and walk away. I bet when came back the fish would be dead on the floor amid the broken bowl. |
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Friction, as one of the entropic effects, allows such zero-sum tactics. While
it may lead to the 'heat death' of the universe as everything drops below a
temperature that allows motion, it also allows us to not be stuck in endless 'reversible' cycles that don't actually lead anywhere. |
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Reversible; You carry something up a hill, and then gain back all the energy expended when you roll it back down.
Ir-reversible;Friction steals some, you can never get it back. |
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//Okay. So there's no chance of anyone getting this far\\ You don't know half of the halfbakers as well as you should, everybody reads this! |
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// bet when came back the fish would be dead on the floor amid the broken bowl.\\ So you also think the fishbowl will move. I had to read your anno twice to really get that. Allow me to ask: did you read the entire body of annotations above [Darkelfan]? It seems to me you did not add much new thinking here. |
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Finally I whish to direct attention to the movie Finding Nemo. The fish in the aquarium in the dentist office seem to have the same idea as posted here and they do finally escape using this same method (allbeit in plastic bags instead of bowls). Absolute proof that it works I would say for it is a good movie and beautifull and beauty is truth, nay? |
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Wow, a pagelong anno regarding the physics of a fish in a ball. Who woulda guesses? |
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What fun! Thanks for bringing this up, {Darkelfan]. I had never read it. I liked your two sets of balls, one backward and constant, one forward and everywhich way. It helped me see it. |
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maywa denki did this idea and i have even seen it working. see link |
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Excellent link, benfrost. That's made my day. |
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Well, [zeno], I wasn't primarily trying to add anything, I was just annoyed at all the silly arguments and felt the need to put down something fairly definitive.
Really, it was just cuz the image was boiling in my chest, and I needed to get it off. |
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Here's something interesting. |
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As the fish moves forward to the edge of the ball, it displaces the water with its own body volume. I do believe the mass of a goldfish is lighter than the equivellant volume in water. Thus, by moving forward, it would make the opposite side heavier, and the ball would roll backwards? |
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I had to think about this. I thought it might be like the question whether a juggler + balls weighs less while juggling the balls than when holding them, since they are being held for less time. (Answer: No.) If the fish weighs less than the water but stays in one place, it must swim downwards, thus exerting an upwards force on the water in the bowl. When the fish is to one side of the centre, this force will create a bending moment, which will create a convective flow, which will translate said moment to the bowl by friction. Just as if the fish were tethered to the bottom of the bowl. So the answer is yes. But this will not be enough to upset the bowl. It will be all torque, no action. |
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What are you talking about? |
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Juggler holds one ball, on a sensitive scale. |
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Throws ball up. Force spikes to about 3.5. |
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Then goes down to 2. There's a wait. |
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Force spikes to same as before, about 3.5, unless the ball is caught very carfully. |
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The reading goes back to 3. |
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The juggler can't tell there's a ball in the air, that's telepathy. |
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How about these three variants: |
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1) Six equilateral struts containing rechargeable batteries, connected to a smaller central sphere that contains a gyroscope. The gyroscope, powered by the batteries is surrounded by and responsive to motion sensors. Whichever side of the sphere the fish is on the ball would be rolled toward. |
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2) Struts as above containing small weights and pulleys and a battery in a sealed ball at the center. Motion sensors would trigger weights/pulleys toward direction of fish and cause ball to shift in that direction as well. |
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3) Just for fun, using either of the above ideas that is the most workable, remove fish and water for speedier motion, anything approaching ball would have it roll in their direction (including a dog, cat or person strolling by). Set in a dark room, it could be quite a surprise (Attack-Sphere?) |
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I would tend to think that the whole concept of using a ball, like a gerbil would use is muddying up the concept here. |
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Why not just stick a small aquarium on a toy car chassis. PIR (Passive infra red) sensors in the various sides of the aquarium tell you where the fish is, and it moves there. |
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Hmm, I think I've got something in the half-oven here. |
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See the "Seth Weiner Terranaut" link, [ye_river_xiv], for the winner of last year's Percival Bartlebooth award. The Bartlebooth Award celebrates the improbable, impossible and incredible in international contemporary art. The Terranaut is quite similar to your proposed solution. |
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This idea is a true Halfbakery Classic - there should be awards for ideas like this. |
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As I finish reading the near-endless annotations on this idea, I can't help but think "I have just lost over an hour of my life that I can never get back. And for what? A really big headache..." |
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Just for the record, I think it could move, as long as the sphere has an air bubble and the surfaces of the floor and outside of the sphere were *very* smooth. |
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All this to find out the damned thing is baked... mm baked fish... |
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Sorry to bring this up again - but I was reading
doctorremulac3's "A Pool That Goes Somewhere"
idea, and had another idea which I originally
thought might be worth launching a new idea, but
quickly found it wasn't. |
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Basically, it's the concept of the swimming pool as
a massive bag. Which carnival prize goldfish have
called home (intermittently) for years. |
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Scale it up to human size, seal the bag really well,
and enlist an army of really bored people with not
a lot to do, and you can swim forward while an
army of volunteers push the massive swimming
pool bag forward, rolling it down hills and
ultimately streets as you go on your gasping way... |
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//I think the fish will have a limited life expectancy since of you seal it in a sphere, there will be no gas diffusion to remove CO2 and replace oxygen.// |
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//What are you talking about?// Sorry, I meant (but didn't say) that *averaged over time* juggling does not alter the weight if the juggler + balls. |
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I'm still fairly sure that a denser-than-water goldfish, on the North side of the sphere, actively swimming upwards to maintain its position, will cause the sphere to roll to the North. A less-dense-than-water goldfish, swimming downwards, will cause it to roll in the opposite direction. A neutrally buoyant goldfish will only be able to move the bowl by treading water, with part of its body out of the water. |
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The water is essentially a treadmill. Whatever
water the fish moves to keep itself up just goes to
the other side of the sphere. |
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It's a closed system. No energy out and no ongoing
redistribution of weight so no movement. It
might knock some water to the other side of the
sphere but it'll bounce back and counteract any
movement so the most that would happen is
it would rock the thing back and forth. |
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You'd need a heavier than water suckerfish to
climb up the side of the thing to
make it move in any direction. It would work but
it would be pretty slow. And by pretty I mean
really. |
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But still, a variation of Lurch's idea of the light
sensors at
the bottom of
the bowl controlling little motorized caster
wheels is the way to
go. Have an array of them radiating out from the
center of the bowl towards the walls. If the fish is
in the middle nothing happens but the closer the
fish swims to any section of glass the faster it
goes in
that direction. No need for the water jets to keep
the fish on station like Corona suggested, it just
moves and steers by using it's body like a joy
stick.
Eventually it might even learn how
to steer, accelerate and even brake and back up.
You'd have the fish equivalent of Neil Armstrong
and it would be interesting to see what it did in
this new world.
Would it greet you when you came home? Would
it creep you out by
following you around late at night? Would it roll in
and interrupt intimate moments? |
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Talk about a cool science fair project. |
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I'm gonna submit this to Mythbusters. (See link) |
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"Can a goldfish learn to drive?" Adam is actually
going to be at a ribbon cutting ceremony at a new
Techshop opening in SF, maybe I'll ruin his day and
say "Hey! Got an idea for your show!" |
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Looking at the failed rolling robot idea (because it
was baked) got me thinking of a great idea: Fish Ball |
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But of course someone already thought of it... :-( |
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Anyways: propulsion will be by friction. Have two of
them, put a Siamese fighting fish in each, and you
have action. I don't want to think of the ensuing
puns. |
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Reality is catching up with this one. <link> |
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aha, great link [swim], the fish's movements aren't random; it's actually driving around. |
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That fishlink needs rotacaster wheels. |
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//Reality is catching up with this one. |
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At last, a way for a goldfish to chase a cat. Suggest 500 horsepower at the very least...and spikey tyres.. |
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I can see the day when a pack of goldfish manage to tree a cat and wait it out with inscrutable piscine patience |
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Thank gosh, I was concerned this was a return of the snow globe meme. |
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Today I saw a roaming goldfish bowl. |
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It was at a zoo, which had a pond with some koi in
it. Floating in the pond was a Perspex (or maybe
glass) hemisphere, about 3ft across. The domed
surface rose up out of the water, and there was
just a little bit of air at the very top. |
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Fish would swim into the dome and up, bringing
them above the surrounding water level. It was
very cool. |
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Not sure of the physics - I assume the rim of the
hemisphere must have been very bouyant to
support the weight of water. And I would imagine
that there would be a substantial negative
pressure inside the dome, but it didn't seem to
bother the fish. |
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There must have been some floats underwater or something, to hold the hemisphere and a what could be a considerable weight of water. |
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Was it definitely floating? It would be easier to fix something like this to a pole than to jigger the correct buoyancy. |
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I wonder if it was initially full of water, but the negative pressure encouraged dissolved gases to come out of solution and form the bubble? |
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I've seen videos of them before, normally they're fixed installations, although making one float wouldn't be that difficult (it's as much about COM as it is about bouyancy, this thing needs a weighted keel). |
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Remember, atmospheric pressure can support a column of water 9.81m high, so the pressure at the top of your little dome won't be very low at all. If it's a metre above the free surface of the pond, pressure at the top of the dome will be ~90kPa and your fish would likely not notice. |
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I beg to differ, (ha, just kidding)... |
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//Was it definitely floating?// I think so. If so, as
[hippo] pointed out, there must have been
significant floats to support the uplifted water. But
maybe it was fixed. |
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Or the water in bowl was regular H2O, and stuff in the tank below was heavy water? |
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I like the idea of how confused fish would be in
heavy water. They'd likely end up stuck on the
surface, for two reasons 1, their swim bladders
probably don't have enough reserve capacity 2, the
lack of protons would render their mitochondria, and
by extension the fish, inoperable. |
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You could put them in (on) mercury. I'd quite like to
watch a frustrated eel trying to get below the
surface. |
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//Maybe an Aibo, or similar robotic dealy with a sealed fishbowl built into it// also //the robotic platform look like one of those battle robots from Robotech or MechWarrior// |
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Unless someone already said it (so many ano's!), 'My Goldfish Is Evil'? |
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<is really far too old to know about that show, looks embarrassed for having mentioned it & shuffles off to read the rest of the ano's> |
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<gives up trying to read all ano's looks round quizzically & raises a hand> |
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Excuse me, but Just out of curiosity, might one enquire as to how many goldfish / scuba equipped hamsters (etc.) gave their lives to settle this particular (2003) disagreement? |
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We can give you the figures for drowned cats, if that's any help ? |
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You'd have to also own up to how many times you rephrased the question. |
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"Until all the cats were dead". |
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[Link] added today is broken. |
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[pluterday]'s current profile page revision happens to be
exactly 15 years old today. |
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