h a l f b a k e r yWhy not imagine it in a way that works?
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OK, so every action has an equal & opposite reaction right? so
if
everyone on the planet runs counter to the spin of the earth
we
should be able to speed it up.
Centripetal force counters gravity so if it spins faster
everyone will weigh less.
Burn fat & lose weight increasing the worlds
spin, lose
more weight from that.
Fantastic! double results for the effort.
What could possibly go wrong.
World Wave
World-wave
[2 fries shy of a happy meal, Oct 12 2019]
Funny hamsters in wheel videos
https://www.youtube...watch?v=X1kcTdzKb_E
YouTube [Skewed, Oct 15 2019]
[link]
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//so if everyone on the planet runs counter to the spin of the
earth we should be able to speed it up// The effect will be
proportional to the mass of the person running. So, we should
just get all the really fat people to do this. The rest of us can
watch, take photos, post videos on Youtube and so forth. |
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Can you film some prototyping on a standard treadmill for us? |
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You don't need to run, just hop, tap the gas, or the brake depending on your direction of travel when the wave passes. [link] |
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What happens when you reach Atlantic City? |
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We're going to have to build a really long bridge. |
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What happens when they stop? Or do they have to
keep going forever? |
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Think about angular momentum. Taking Earth and
all it’s people as a closed system (that is, ignoring
things coming from/going to outside the
atmosphere), angular momentum is conserved.
So running people/accelerating/braking cars,
anything that starts “from rest” and returns “to
rest” (at the same height) won’t have a net effect
on
spin speed. |
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If you had a large elevated mass, and redistributed
it at a lower elevation, that would have an effect.
So if you bulldozed the Himalayas and tipped the
rock into the Marianas Trench, you would actually
increase the spin of the earth. |
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//if you bulldozed the Himalayas and tipped the rock into the Marianas Trench, you would actually increase the spin of the earth// - I'm happy for you to try this to test your theory, but I'm not certain it'll work. When the Himalayas are pushed into the Marianas trench, you're right that you're moving mass closer to the Earth's centre of rotation, but at the same time, you'll also be moving the mass of displaced water away from the centre of rotation (as will be seen in the raised sea levels and concomitant wiping out of coastal cities around the world and huge loss of life). |
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//What happens when they stop?// |
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That's why we need a really long bridge, at least two. |
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You can't turn around & walk back the way you came, equal
&
opposite reaction remember, to get back to where you
started while
avoiding cancelling out any extra spin you achieved you
have
to go all the way around. |
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//you'll also be moving the mass of displaced water// |
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Stone is denser
than water, it's why it sinks, so less weight gets displaced
up, which means? |
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//which means//
...the total moment of inertia has reduced, so
angular velocity increases to conserve angular
momentum. |
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//What happens when they stop?// |
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This is the problem, you only get an effect while people are
accelerating up to speed. Perhaps if they were vaporized by
a large laser once they attained Vmax? |
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No they can stop, they just can't turn around & walk back. |
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// //which means// ...the total moment of inertia has reduced, so angular velocity increases to conserve angular momentum.// - yes you're right, it would work. We need to do this anyway, to counteract the gradual slowing down of the Earth's rotation caused by tidal drag from the moon. |
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//Perhaps if they were vaporized by a large laser// the vapour would slow down and so there would be no net advantage to this action. |
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//vapour would slow// ahem //No they can stop, they just
can't turn around & walk back.// |
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//they can stop//
...no, it’s the force they exert while accelerating
that adds to the rotational speed. If they stop, the
deceleration (reaction force) undoes that. Even if
they turn North (say), or are blasted to atoms by a
laser - if their mass is decelerated within the
Earth-atmosphere inertial system, it undoes the
gain from accelerating in the first place. |
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So they have to keep running west, keep on
running... forever. |
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Pink Floyd “you run and you run to catch up with
the sun but it’s sinking...” |
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One of the problems with this idea is that the entire
point if losing weight is that other people are not. |
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Actually, I’ve just realised that rocket launches to
orbit are stealing our angular momentum. They
often launch eastward to take advantage of the
earth’s spin. By doing that, they slow down the
rotation.
We’ll get it back again if/when they de-orbit, but
still! NASA has made our days longer! |
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//it’s the force they exert while accelerating// |
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Um no, either you're yanking my chain, having a senior
moment, or I am. |
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It's
the
force they exert while 'moving', every step exerts a force,
not taking another step doesn't cancel that force, you have
a football in space, you push it away from you (& you away
from it) with your foot.. does it ever stop moving away
from
you. |
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Think a hamster in its wheel running as fast as it can then it
stops, if you were right the wheel will stop dead when
the
hamster does. |
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It doesn't [linky] 1:14 is one of the best. |
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The
wheel slows &
eventually stops due
to friction in the bearing (& air of course) but not
because the hamster stopped running. |
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//having a senior moment// If your hamster wheel was in space, the wheel would spin only while the hamster walked. On
earth, the wheel gains additional motion as the hamster climbs the sides of the wheel, and its additional potential
energy is converted by gravity into kinetic energy. Given a heavy enough wheel, some of that energy goes into its
intertia - which would keep it rotating if you vapourised the hamster. But in space, without that free input of gravitational energy, the
hamster and the wheel must exert equal and opposite forces on one another that cancel out. |
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Imagine walking on a playground roundabout rotating on a perfectly frictionless spindle. Without touching the floor,
your intended motion clockwise ought to be equally and oppositely counteracted by the roundabout's motion anti-
clockwise. If you stop walking, then the roundabout should also come to a stop beneath you and you'll remain exactly
where you started. |
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If there's any residual motion then the laws of thermodynamics will have been violated, and you'll be on the money for
inventing some kind of perpetual motion/energy device. |
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Otherwise, you'd be able to "swim" in space by waggling your arms about to conjure up free motion. |
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//If your hamster wheel was in space, the wheel would spin only while the hamster walked// - I think the wheel and hamster would rotate in opposite directions around their combined centre of mass, which would look slightly different to the wheel spinning around its axis. |
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No, really not! Sorry if it seemed like that. |
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Here's a different way of looking at it: |
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You have a 100kg mass on a level frictionless track (in a vacuum) pointing west. There's a big spring that will accelerate the mass at 10m/s^2 for 1s. |
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The fixed end of the spring is attached firmly (through some structure) to the ground. |
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When you release the spring, a force of (100*10) = 1000N acts on the mass accelerating it, and a reaction of 1000N acts (through the structure) on the ground - for 1 s. |
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The mass travels along the frictionless track at 10m/s for as long as you like - and then it hits a buffer at the other end, where it's brought to a stop at 10m/s^2. The buffer is attached to the ground, and again exerts 1000N, for 1s |
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Between those two points, the mass exerts no east-west force on the earth. When it's launched, it applies a force to the planet, accelerating the spin very slightly. When it reaches the buffer, it applies the opposite force, slowing the planet's spin back to exactly it's original speed. |
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The reason your feet continue to exert backward force when you're running at a constant speed is to overcome air friction (and creaky joints in my case). |
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I think [hippo]'s got me, your's is longer so I've not skimmed
it
yet. Dang! Remember I did say //or I am// about that
senior
moment option. I'm going to have drag up some YouTube &
Wikipedia to satisfy myself where (if, I think it may have)
my
mind failed me now. |
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//No, really not! Sorry if it seemed like that// |
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Don't be (unless you are ;p) my senior moments aren't your
fault. |
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