Table of Contents

A Guide to Microgravity for All Ages

The Uniqueness of Microgravity Environments

The environments of microgravity have unique characteristics. Microgravity, as discussed before, is achieved by putting objects in free fall. Free fall can be interpreted quite literally to mean that an object is free to fall -- there is nothing to oppose its fall.

On earth, the ground opposes your fall. A parachutist's fall is opposed by air drag on his body. Air drag can't stop the fall, but it does slow it down. Even in orbit, there is air drag. The atmosphere is very thin, so it is a very small amount, but it is still there. The extent to which gravity seems to disappear, or the quality of microgravity achieved, is the extent to which the forces resisting your fall are eliminated. If these forces were eliminated completely, you would be in a zero gravity environment. Free fall or microgravity is an environment in which forces resisting your fall are very small.

The reduction or absence of resistive forces has external and internal effects on your body, both with important consequences. Gravity and resistive forces affect your body externally.

On earth, gravity acts uniformly on all parts of your body, but resistive forces act only on contacting surfaces like your feet and the ground. The total force on your body is zero, but because the resistive force opposing gravity acts only on your feet, your body reacts to distribute this force evenly. In a microgravity environment, there are no resistive forces and therefore no internal force distribution. This affects all objects and is a very significant internal effect of microgravity.

Things behave differently in microgravity environments than they do on earth. Forces which were negligible on earth become influential in microgravity. An example of this is a drop of water and a soap bubble. On earth a drop of water flattens out due to gravity. A soap bubble on earth retains a spherical shape because the surface tension forces are large compared to the resistive forces. Resistive forces are equal to weight in magnitude, so where weight is small (soap bubble), then resistive forces are also small. In microgravity or weightlessness, the resistive forces are absent, so even for a heavy droplet, surface tension will still dictate its shape-a perfect sphere.