Re: Gs needed to walk

Wasn't it Robert Grumbine who wrote:
In article <1176550331.191524.62360@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
<chornedsnorkack@xxxxxxxxxxxx> wrote:
How many gs do people need to walk on a horizontal surface in
ordinary, 1-atmosphere, mostly nitrogen air?

People can walk in water as deep as their shoulders. But it is not the
fastest or most effective way of moving. Water offers large resistance
to people walking upright, and as buoyancy decreases the load on feet,
feet lose traction. In deep water, although standing on bottom is
practical and walking is possible, swimming is faster and spends less
energy.

In air, the air resistance is much lower than water resistance on the
same speeds. But obviously, in case of low gs, feet would lose
traction. In exactly 0 g, there would be no traction under feet, and
no way of moving except by swimming in the air.

How many gs are necessary before feet can be used to move on the
surface (rather than using hands, feet and torso to swim in free air)?
0,01g? 0,001g? Any estimates?

There was some work published in Nature (iirc, elsewise it was
Science) within the last 10 years on the walk-run transition speed
at different gravities, from 1 g to ca. 0.1. Hard to set up the
equipment to go much below 0.1. The systematic result is that one
could walk more rapidly under higher gravity. As the gravity dropped,
running became more efficient than walking at lower and lower speeds.

There was no particular limit to the gravity required for running.
But as the gravity drops, it moves to a more and more bounding
motion. For sufficiently low gravity, it would probably look more
like a long jumper -- multiple striding motions between footfalls.

There must be a point where there's not enough force between a foot and
the ground for friction to provide a sensible amount of forward thrust.

The Vomit Comet achieves about 0.001g at best, and people don't seem to
walk in that. That's probably not a useful example, because the 0.001g
may well not be in the direction that the passengers are expecting it,
and there's nowhere near enough room for them to move around by
bounding. Nevertheless, I suspect that it becomes more efficient to move
around by pulling yourself along the ground with your hands, or to push
off from vertical surfaces, like people do in the Shuttle and ISS.

Since we're talking about moving in an atmosphere, I guess we're inside
something with a ceiling. As gravity gets lower, the bounding motion
takes you higher, and there's going to be some point at which the
ceiling either gets in the way, or becomes useful for bounding off.

--
Mike Williams
Gentleman of Leisure
.

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