Naked Science Forum
General Science => General Science => Topic started by: Rawlins, Barry G on 06/09/2009 15:30:03
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Rawlins, Barry G asked the Naked Scientists:
Dear Chris and team,
My son and I were wondering: if Usain Bolt could sprint on the moon, without being hindered by extra weight - space suit or breathing equipment - would he run faster or slower than on earth?
I believe gravity is weaker, but we're not sure if this is a benefit for locomotion?
Many thanks, Barry and Joshua
Nottingham, UK
What do you think?
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Our limbs ( or those of champion sprinters) are fairly optimal for Earth conditions. I think the problems of matching our limbs to the Moon gravity could limit top speed. Both acceleration (traction) and top speed would be affected. You would need to lean much further forward to keep from rotating backwards (something we do automatically down here) if you want good acceleration. This would be difficult or even impossible. As for speed; you would be effectively in a lower 'gear' than optimal.
I think that, with suitable extensions, like the 'blades' used by Paralympic runners, it would be possible to run much faster. Each stride could be much longer as the time off the ground would / could be at least twice that on Earth. I think that's what the good old equations of motion imply. Contact with the ground slows you up so less contact would mean faster.
There would be a long learning time involved and you'd have to clear it with the record keepers.
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In theory, if the legs have to support less weight then they should be able to put more effort into moving. In practice though, traction might be a problem. I also recently heard someone talking on the radio about whether it is possible to bring the sprint times down much further because as the speed increases the runner spends less time with their feet in contact with the ground: to go faster you need to apply more force to the ground but as you go faster you have less time to do so. We also need to remember that it's not just a case of strength either; power-lifters have immensely strong legs but don't make good sprinters because they can't move their legs quickly enough, so a sprinters leg muscles not only need to deliver the necessary force but do so quickly.
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I agree with both the above. The astronauts who landed on the moon had a different way of moving which was a kind of skip. They also had a huge amount of mass (at least it would have weighed a lot on earth) on their backs and were in cumbersome space suits. They found this to be a better way of getting about. It was also important that they didn't lose their balance because getting up with the suits they had on would have been difficult.
In theory you should be able to go faster on the moon. I guess long running spikes might aid traction. One problem would be that the stride length would be large; it is likely that the fastest pace would involve lengthy periods off the ground on each stride. A problem would be maintaining your orientation accurately and consistently enough so that you didn't end up in an untidy heap on the surface after a few paces. It may even be worth a runner carrying a sizeable gyroscope to retain orientation. It makes me think that a two wheel bike with bulbous, spiked tyres would be a useful vehicle. Do you think I should patent it. Oh blow, I've just disclosed it. Well nobody else can patent it now then.
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Listen to the answer to this question on our podcast. (http://www.thenakedscientists.com/HTML/podcasts/show/2009.09.05/)
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There is a limiting speed corresponding to how fast you can move your leg backwards. I don't think it is all that fast - as people trying to jump/run off an old Routemaster Bus in motion or trying to run downhill will find.