Demonstrating reduced gravity

The effects of gravity are so inerent in life on Earth that we often ignore how these effects complicate and sometimes mask fundamental processes in chemical and physical systems. To highlight the importance of gravity, we built a series of experiments, appropriate for the classroom, to demonstrate how the behavior of common physical systems change when gravity is nearly eliminated. Based on Newton's law, F = ma, Einstein realized that a body of weight W = mg while stationary on the Earth, would appear weightless if it were in free fall. Imagine that the body is within an imaginary box (i.e., frame of reference) that is falling at the Earth's gravitational acceleration (a = g). Relative to the falling frame of reference, the body is motionless, there is no net acceleration, and therefore W = 0. The state of free fall is often referred to as weightlessness or microgravity. In several research labs around the world, scientists take advantage of this idea and perform "gravity-free" experiments in drop towers, airplanes, and spacecraft. Drop towers typically provide several seconds of microgravity and, as the name suggests, operate by hoisting the experiments to the top of a tower and dropping them. For example, NASA Lewis has two towers; one provides a fall distance of about 25 m and the other provides 130 m. These fall distances correspond to 2.2 and 5.2 s of microgravity time, respectively. The Japanese Space Environment Utilization Center in Hokkaido, Japan has a 10-s drop tower with a fall distance of about 500 m, roughly one-third of a o 0 oo o