The effects of gravity are so commonplace that people rarely notice them. People are used to living under the pressure of Earth's gravity (1 G), and so when the amount of gravitational force they experience increases or decreases, the difference becomes noticeable.

The factors that cause these differences in G forces are mass, motion, and density. A person's mass stays the same in any location but is dependent on the amount of gravity that person is experiencing. When a person experiences zero g forces, that person's mass is unchanged but he or she still experiences weightlessness. Scientists refer to zero g as microgravity because even in zero-g environments there are small amounts of gravity. Those amounts are too small to provide significant levels of resistance for humans.

Most people believe that space travel is the only way to experience microgravity, but that is a misconception. There are...