The other day I was watching my 8 year old grand-daughter run on the playground. She was running like a girl - like Jackie Joiner-Kersey to be precise. It appeared that her form was perfect - that every move she made was focused on moving forward with maximum effect and minimum effort and with almost incredible grace (says the proud grandpa).

So, in a novel I'm working on I decided to have one of my adult female characters do the same - but she lives in an environment with lunar (1/6 G) gravity and a full atmosphere. (How that is true is a different matter - don't go there.) My woman is athletic and has great endurance, so she's going to "bound" that is run in a manner that means she leaves the ground for significant distances, but in a manner that means she can keep this up for many kilometers (with occasional walking rest periods).

How far will each bound take her and what will her effective speed be? (She's not racing - she's just covering ground quickly and easily. I plugged in seven meters per "step" but that was just a guess.)

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    $\begingroup$ Well, assuming a normal stride of a little over a meter, one might think that 1/6 gravity would multiply that by 6, so your seven meter stride may not be off the mark. But I'm not a physicist, and I can't work the equation in my head currently to give you a definite answer. $\endgroup$ – Isaac Kotlicky Mar 1 '15 at 7:39
  • $\begingroup$ Air resistance would be a factor here, acting to slow you down if you tried to make the strides too long. $\endgroup$ – Tim B Mar 1 '15 at 10:50
  • $\begingroup$ @Tim B♦: I'm not a physicist either, but it seems to me a planet with such low gravity wouldn't be able to hold down much of an atmosphere (there's none to speak of on the moon), so air resistance couldn't be a factor. To my mind a major limiting factor would be the difficulty of gaining sufficient traction to avoid most of the muscular effort going into vertical rather than horizontal motion. $\endgroup$ – FumbleFingers Mar 1 '15 at 17:06
  • $\begingroup$ @FumbleFingers Atmosphere is not linear with gravity, Venus for example is an excellent example - it has a lower gravity than earth but a much much thicker atmosphere...we don't actually know what the limits are yet...although I agree lower gravity generally means less atmosphere. $\endgroup$ – Tim B Mar 1 '15 at 20:51
  • $\begingroup$ I should have specfied that indeed, the atmosphere is enclosed (thick very large dome - although that's not exactly what's going on. $\endgroup$ – DavidTrump Mar 2 '15 at 0:39

For astronauts, the limiting factor for running on the moon is the bulky mass or a restrictive spacesuit. However, in your scenario, this is eliminated due to a standard atmosphere (such a situation would be feasible in an enclosed area, such as a lunar base, or under a large dome).

Fortunately, NASA scientists have tested this. Not on the moon directly, but with treadmills, on the DC-9 aircraft that flies parabolic trajectories to simulate low-gravity (or zero-gravity) environments. Keep in mind that these trajectories can only be maintained for a limited time (about 20 seconds in this case), which prevents the subjects from necessarily building up a whole lot of speed. The article I found doesn't report a maximum running speed.

Instead, it reports the transition speed. This is the speed at which a person switches from a walking gait (in which there is a phase with both feet on the ground) to a running gait (in which there is a phase with no feet on the ground). On earth, this transition happens at about 4.5 mph; in lunar gravity, this transition occurs at a slower speed of 3.13 mph. Interestingly, the researchers had predicted an even lower transition speed of only 1.8 mph, which demonstrates how hard it can be to predict these things without actual experiments.

As for top running speed? It's hard to say.

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    $\begingroup$ Granted, this is probably a better answer to the question "How fast can one walk on the moon before it becomes more natural to begin running?" $\endgroup$ – Caleb Hines Mar 1 '15 at 20:35
  • $\begingroup$ That's good information Caleb and sets me up for more accurate descriptions of additional scenarios - Thanks $\endgroup$ – DavidTrump Mar 2 '15 at 0:38

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