Question

How zero gravity is created in biological experiments on earth

The only way to create true microgravity on Earth is in an airplane flying a "free fall" trajectory that gives about a minute of zero g. The main NASA plane that is used for these experiments is known as the "vomit comet" for obvious reasons. Most biological experiments require long exposure, of course. For tissue samples, one can simulate many of the effects of microgravity with a slowly rotating drum, where the direction of gravity is constantly changing; it is never zero, but it averages to zero. Another approach for humans is a bed rest facility. If people lie flat on their backs in a bed for several weeks, they suffer many of the same effects (such as loss of bone calcium) that they do in microgravity environments in space. David Morrison
NAI Senior Scientist
September 4, 2007