Expert: Courtney Seligman - 5/21/2009

Question
mars has a gravity 38% that of earth...if earths gravity was the same how fast will a man be able to run or for that matter the speed of any object on earth like a speeding car a running animal or a speeding bullet?

Answer
The difference in gravity wouldn't affect how fast things could go -- only how fast they fell. For things like baseballs or golf balls, that would affect how far they would go, not because they would go any faster, but because it would take longer for them to rise and then fall, so they could go farther at the same horizontal speed.

There would be a slight effect on the speed of very fast objects, for which air resistance is important, because with a lower gravity the atmosphere would expand toward space, and become less dense. As a result, insofar as speed is limited by air resistance, higher velocities could be reached. But at speeds reached by men or animals, air resistance is relatively insignificant, so their speeds would be unaffected.