Weightlessness

Weightlessness is the experience (by people and objects) during freefall, of having no apparent weight. This condition is also known as microgravity (see below).

Related Topics:
Freefall - Apparent weight

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Weightlessness in common spacecrafts is not due to an increased distance to the earth; the acceleration due to gravity at an altitude of, say, 100 km is only 3% less than at the surface of the earth. Weightlessness means a zero g-force or zero apparent weight; acceleration is only due to gravity, as opposed to the cases where other forces are acting, including:

Related Topics:
Acceleration - Gravity - G-force - Apparent weight

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

• standing on the ground, sitting in a chair on the ground, etc. (gravity is cancelled by the reaction force of the ground)
• flying in a plane (gravity is cancelled by the lift the wings provide) - see below for special trajectories which form an exception
• atmospheric reentry, landing on a parachute: gravity is opposed by atmospheric drag
• during an orbital maneuver in a spacecraft: the rocket provides thrust

The difference is that gravity acts directly on a person and other masses, just like on the vehicle, while forces like atmospheric drag and thrust first act on the vehicle, and through the vehicle on the person. In the first case the person and the vehicle floor are not pushed toward each other, while in the other cases they are.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

 
Weightlessness: Overview ►