Shruti N.

Space has gravity. The planets are revolving around the sun is just because of gravity. The centripetal force is balanced by force of gravity. So your question needs to be modified. You can say about atmosphere on different places of the universe. Like its difficult to walk on the surface of moon. Well, it's also about atmosphere. When you walk on Earth, there is an air column "keeping you in place", pushing you down, beside gravity. Also, you're used to walk against air resistance. A SciFi scenario: take beings from denser environments, like water, and let them walk in a thinner environment, like on Earth's surface. Their muscles may be too developed and the force they use to push down when taking steps may be too much. And if you try to control that... welcome muscle soreness. Also, the way you walk, or navigate, even on Earth, is learned, it's not a natural reflex. Your brain is used to make certain calculations and it takes time to adapt to a new reference system.