Zero Gravity

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Zero Gravity

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 ways to alter the amount of gravity a person feels on Earth, including roller coasters, jet planes, extended freefalls, and underwater environments. The turning of the riders at fast speeds on a roller coaster produces variations in the amount of gravity felt by the passengers. When the cars reach the top of a summit and begin to plummet, the passengers experience a moment of microgravity. The upward and downward gravitational forces are balanced for a split second, leading to the sensation that one is floating. When the forces are unbalanced, the car plunges downward, leaving microgravity behind.

The same principles apply to jet planes when flying specific courses. Probably the most famous plane that creates microgravity experiences is the Vomit Comet. This KC-135A plane, a modified 1950s Boeing airplane, performs a series of parabolic maneuvers that cause short, repeated periods of microgravity. Each flight on the Vomit Comet usually lasts a couple of hours and provides dozens of microgravity experiences that last 30 seconds to 2 minutes. About half of the first-time passengers on the Comet get sick from intense g forces during ascent or during the dive run that creates the microgravity experience. Every astronaut who has flown in space has first experienced microgravity on the Vomit Comet, and today scientists and students conduct zero-g experiments aboard it.

Extended freefall from high altitudes offers a near-microgravity environment. Skydivers have a few minutes while falling in which they are tricked into thinking they are floating. Despite this trick, eventually skydivers must use their parachute to help control their descent to prevent tragedy. Once the parachute is opened, divers still experience a floating sensation, but only for a brief period.

Underwater, astronauts dressed in space suits train by performing mission tasks. This is the most cost-effective training ground for microgravity experiences. The National Aeronautics and Space Administration has gigantic underwater tanks for this purpose. The natural buoyancy creates an experience similar to microgravity.

see also Living in Space (volume 3); Kc-135 Training Aircraft (volume 3); Long-Duration Spaceflight (volume 3); Microgravity (volume 2).

Craig Samuels

Internet Resources

Aviation Magazine and News Service. "NASA's Vomit Comet: Hitchin' a Ride on a Buckin' KC-135." <>.

NASA. "Ask A High Energy Astronomer," <>.

News Channel 2000. "'Vomit Comet' Could Be Grounded." <>.

Purdue University. "Aspiring Astronauts to Ride on the 'Vomit Comet.'" <>. "Low Gravity, Zero G, and Weightlessness." <>.