[alancalverd]

The atmosphere we have is in a sort of equilibrium between gravitational attraction and thermal loss to the vacuum of space. In the absence of evidence for interplanetary piracy of artificial fertiliser (why? There's plenty of free bullshit right here!) I rather feel that other planets obey the same laws of physics. Being impatient I'd probably use a diving bell rather than wait around for alien spacecraft to modify the atmosphere to fit the OP.

[Bored chemist]

The atmosphere we have is in a sort of equilibrium between gravitational attraction and thermal loss to the vacuum of space. In the absence of evidence for interplanetary piracy of artificial fertiliser (why? There's plenty of free bullshit right here!) I rather feel that other planets obey the same laws of physics. Being impatient I'd probably use a diving bell rather than wait around for alien spacecraft to modify the atmosphere to fit the OP.

So... you are prepared for magic to change g but not to change the mass of the air.
OK, you are entitled to your view on that.
But saying that a diving bell was the only way is still wrong, isn't it?

The atmosphere we have is in a sort of equilibrium between gravitational attraction and thermal loss to the vacuum of space.

Which bit?
The stuff at the top of Everest is very "thin" compared to the stuff at ground level.
But g is pretty close to the same.

So we can change the atmospheric pressure (independently of g)  over a large range by climbing a mountain.
No diving bell required.

[Halc (OP)]

Found this:
--- "Reducing-gravity-takes-the-bounce-out-of-running"
A scientific study, with actual data collected, about the running stance and gait adopted in simulated low-G environments.

Their conclusions:  Mainly that the gait is adjusted so as to keep the centre of mass extremely flat and level, i.e. almost all bounce is removed.  Their models suggest this is energy efficient (they use "an impulsive model of running" developed by Rashevsky and Bekker - although these people contributed at different times and not collaboratively).

Cool link. I watched their vid, and they have guys running at about 2 m/sec, hardly an attempt at speed. It wasn't their point. The vid shows normal and moon gravity, but the data collected shows stuff up to about 2/3 g.

I'm not so sure about the energy-efficiency theory. Humans are already notoriously low efficiency when it comes to running. Most creatures of our mass use less than half the calories to maintain a specific pace.
The low-bounce gait helps them maintain the natural rhythm of a mild jogging pace. A bigger bounce would mean an uncomfortably slow rate at which the legs are swapped. At a faster running speed, the running gait would probably become completely unfeasible as the legs would have to move too quickly to match the speed of the ground under you, and there's little point to doing it one leg at a time.

The test as done cannot realistically simulate a real run since there is no wind resistance, as you point out. It's on a treadmill. Great for the sort of data they're collection though.

They didn't seem to have a wind fan or anything to re-create the effect of air resistance.

At 2 m/sec, it's effectively negligible anyway. People can walk far faster than that, but only at worse energy efficiency.
I'd love to see a speed walking race on the moon...

Just for amusement, here is Usain Bolt trying to sprint in low G:

A vomit comet vid. Yes, it's just fun. No practice or sustained gaits, and it's all acceleration, no actual speed, and they're wearing only socks.

Regards, and thanks for the on topic post, unlike the A/B twins...

Given infinite time what speed would he achieve.

Probably little different than at full gravity.

If 99.999etc of his energy was directed forward rather than up I surmise this must be fastest

It's not about energy, but about force. If all the force is directed forward, you'd perhaps go faster, but how exactly are you going to apply force that way, especially with socks on what looks like a vinyl padded mat. Those guys had nothing to give them any traction.

The ion drive doesn't have air resistance working against it. It's mean to be used in a weightless vacuum, an environment where an athlete would make zero progress at all by attempting to run. He may have all the energy he wants, but he has nothing against which to apply a force.

[alancalverd]

Interesting article in the current Physics World (Institute of Physics) on hill walking on the moon.

[Eternal Student]

Hi.

Interesting article in the current Physics World (Institute of Physics) on hill walking on the moon.

   Usually, someone gives a brief mention of what was discussed, otherwise we have to guess.  This is what I'm hoping the article was about:

   The hills in my area have "post boxes" hidden on them.  These are basically stamps (ink stamps) you can collect and people who do a lot of walking have books full of stamps which are they are often very proud of.  I was in the 100 club myself (I had one hundred stamps) when I was younger.   Some stamps are extremely rare like the Dartmoor Pony stamp.  These are supposed to be carried by the person who finds it and left at the very next post box they visit, so the stamp literally roams the whole of the countryside and could be anywhere.  I still look for it myself sometimes.
   Do you think the Dartmoor Pony stamp could now be on the moon?   That would be just amazing.  I thought it would be a few more years before we really had an active community engaged in hill walking on the moon but I guess things do change fast.

Best Wishes.

[alancalverd]

It's quite a long and rambling article (pardon the pun) but it introduces the required force F_c = mv²/r to keep the propelling foot in contact with the surface when the center of mass rotates at v in an arc of radius r during the stride.

This leads to the Froude number f = v²/rg. If f >1 the foot leaves the surface so this describes the transition  from walking (the object of the article) to running, but also limits the impulse per stride, and hence acceleration, when running. It turns out experimentally that the limiting value of f is actually closer to 1.25 if you swing your arms and the free leg, but in practice lunar astronauts tended to lift off at f ≈ 0.5 due to the stiffness of their suits.

So there's the basis for some integral equations, assuming an infinitely flexible and weightless space suit or Halc's Planet on which g is variable and a normal atmosphere is attached by magic!

I have volunteered for a one-way trip to Mars and will be happy to take a Dartmoor Pony stamp with me. Or maybe a Jurassic marine fossil from Cambridge for the amusement of the next generation of explorers.

 

[Petrochemicals]

If 99.999etc of his energy was directed forward rather than up I surmise this must be fastest

It's not about energy, but about force. If all the force is directed forward, you'd perhaps go faster, but how exactly are you going to apply force that way, especially with socks on what looks like a vinyl padded mat. Those guys had nothing to give them any traction.

.

That's the infinite time component, minimal friction still creates a force built up over time would be advantageous. The air resistance is propably key to it.

[evan_au]

Videos of astronauts on the ISS suggest that they don't use their feet very much, and mainly rely on upper-body strength. They use handholds, so they aren't limited by contact force due to gravity.
- This suggests that in very low gravity, a chimpanzee (with prehensile hands and feet) would be faster than a human in a flat-footed shoe, provided the environment had plenty of "hand-holds"

At extremely low g, but normal atmospheric pressure (eg in some future, much larger space station), it would be faster to strap some wings on feet and hands, and fly like a bird.