I'm not 100% on the science so please be gentle with me.
Every schoolkid knows that a stationry exercise bike can be used to generate enough electricity to light a bulb, if the bike is pedalled hard enough and for long enough. However, as anyone whose practised this exercise will tell you, the effort involved far outweighs the result. You just don't want to be cycling for all your worth in order to run one electric light bulb. The only practical application I've seen of this is as a generator for a lamp affixed to the front or back of a normal bike, but even these tend to flicker depending on the speed of the bike and don't really work very efficiently.
But how would this translate to space and the laws of inertia? Theoretically if you spin a bicycle wheel in space there is no air friction to slow the wheel and no ground friction to stop the wheel so the wheel just keeps spinning. So affix a bicycle wheel to the top of a space shuttle with its rear wheel in the air then place the rear wheel on a metal roller which is fixed on a stationry axle. The roller is connected to the generator which produces electricity when the rear wheel turns. In a high gear an astronaut would not need to expend very much effort at all in order to produce the electricity needed to light a lighbulb. In fact I'm not sure you would need the astronaut. Just spin the wheel once and it should keep spinning for a long time powering the generator and providing electricity. The friction between the roller and wheel would be very low and there'd be no air friction at all.
What would happen if you dumped the bicycle concept and made this on a huge scale. Weight in zero-g doesn't make a difference so you can have a massive spinning wheel, or lots of massive spinning wheels, rotating against rollers attached to generators making power with minimal outlay.-- Nickynackynoo, Jul 04 2003 (Not really related, but cool) http://www.themepar...ure.com/screamh.jpgEyes closed, I had the feeling of riding a sine wave. [half, Oct 04 2004, last modified Oct 05 2004] Only just related, but V.Cool http://expn.go.com/...001/0330/16264.htmlThe biggest G Differential on a bike?? [gnomethang, Oct 04 2004, last modified Oct 05 2004] Flywheels http://www.wired.co.../8.05/flywheel.htmlAlready being done. [Anarch, Oct 04 2004, last modified Oct 05 2004] Pedalling that bike in sapce will result in the same thing that pedalling it on Eaeth does: you will be storing energy in the spinning wheel. On Earth, friction with the air and the bearings will gradually leech energy from the wheel, slowing it down and leaving less to power that lightbulb. Using magnets, you can create a device that is only slowed by the air.
In space, you can make a spinning wheel that doesn't even lose energy to friction from the air, because there isn't any. So it will go on spinning a whole lot longer. (Presumably, over millennia, friction and/or collisions with the solar wind and other cosmic particles will have an effect.)
But you still ain't gonna get any more energy out of it than you put in. That poor astronaut will still need to cycle for ages to light that lightbulb, and I can think of much easier and cheaper energy sources in space (solar power being the most obvious).
Astronauts do need to exercise a lot to keep their bone and muscle mass up, though, so you could always sell it as a straigthforward exercise bike.-- DrCurry, Jul 04 2003 In this house, we obey the laws of thermodynamics.-- neelandan, Jul 04 2003 I've experinced 0 g's on a bike. I've also experience 5 g's on a bike. (irrelvant link)-- half, Jul 04 2003 thanks for the howstuffworks link. Speaking from the perspective of a moron (as opposed to a condescending twit, no offense) I find that website so much more understandable than nasa.-- Nickynackynoo, Jul 04 2003 keeping your head above water here, nicky, you are NOT a moron-- po, Jul 04 2003 //I'm not 100% on the science so please be gentle with me. // LOL!
Astronaughts spend an inordinate amount of time exercising just to keep their muscles from deteriorating. This energy is wasted and could theoretically be used.
HOWEVER, you'd save much more money and energy just cutting down the weight of the exercise bike.-- FloridaManatee, Jul 05 2003 "Does the simple act of current generation impart a contact-less friction?" Yes.-- phoenix, Jul 06 2003 Imagine pulling to magnets apart. That would be a simplified description of the force causing the generator to slow.-- Zimmy, Jul 07 2003 //I'm not 100% on the science so please be gentle with me. //
When you find yourself saying that, it's usually a good sign that you should back away from the computer and save yourself from the onslaught.
So many issues, but just two for starters: // rear wheel on a metal roller which is fixed on a stationry axle // Presuming you mean 'stationary' - please define it as it pertains to your example. If you mean 'not moving in relation to the space station', explain how you would keep it 'stationary'.
Secondly, the generator will stop your wheel. Fairly quickly, I'd imagine, with nothing keeping the wheel moving except inertia.-- waugsqueke, Jul 07 2003 Don't want to muddy this up with equations so I'll explain it as simply as I can. In order to get energy out, it has to come from somewhere. In this case, you're turning the energy stored as angular momentum into energy in the form of electricity. To make one, you must, without exception, sacrifice some of the other. Picture a generator as some coiled wires spinning within some stationary permanent magnets. While generators come in many forms, this is the simplest. When you move a wire through a magnetic field, you get a voltage proportional to the velocity of the wire and the strength of the field. If you increase the number of turns of wire (a straight wire is a half-turn), you increase your voltage. If you're familiar with electromagnets, you know that if a current is flowing in a coil of wires, you make a magnet. Whenever you're drawing current from your generator, you're turning the coil of wires into a magnet itself, simply by the virtue of flowing current. This is where the "pulling two magnets apart" comes in. The direction of the current induced in the coil sets up a magnetic field in line with the one it's passing through. This wants to pull the coil back into alignment with the permanent magnets. This is the force you are working against, and this is what will slow down your flywheel. Basic thermodynamics at work, you can't get something for nothing.
It's not really friction at all, I believe the correct term is "inductive drag", and it can be extremely strong. Diesel-electric locomotives use this principle to supplement their brakes. They just hook the motors up to huge banks of air-cooled resistors and dissipate the energy as heat.-- Freefall, Jul 07 2003 //When you find yourself saying that, it's usually a good sign that you should back away from the computer and save yourself from the onslaught.//
I post ideas, therefore I am. I may not be Stephen Hawking but I'm learning. The curve steepens thanks to you guys at HB. And what is this speak of onslaughts? Constructive criticism, educated remonstration, the odd insult. Gravy for the soul if you ask me and I'll back away from nothing. Freeeeedom!!!-- Nickynackynoo, Jul 09 2003 You'll fit right in, then.-- RayfordSteele, Jul 10 2003 Well, no problem, but I wish you hadn't edited your last anno. Now my refering to myself as a moron is completely out of context :)-- Nickynackynoo, Jul 11 2003 random, halfbakery