Microgravity

Microgravity is a condition in which apparent weight is very small because objects and their surroundings fall together. It occurs in free fall, not only in space.

Free fall: Motion in which gravity is the only force acting on an object. Shared gravitational acceleration makes objects and their surroundings appear weightless.
International Space Station: A crewed research laboratory in low Earth orbit operated by an international partnership. Its orbit provides a long-duration platform for microgravity experiments.
Gravity: The interaction that attracts masses and governs motion on astronomical and everyday scales. Microgravity does not mean gravity is absent; gravity drives the shared fall.
Zero gravity: An idealized condition in which gravitational acceleration is exactly zero. Microgravity is not zero gravity; orbiting spacecraft remain within Earth's gravitational field.
Equivalence principle: The principle that locally, acceleration and gravity produce indistinguishable effects. It explains why a freely falling frame suppresses the sensation of weight.
Drop tower: A facility that produces brief periods of free fall by dropping an experiment capsule. Drop towers create short microgravity intervals for controlled experiments.
Apparent weight: The support force measured by a scale or felt by an object in contact with a surface. Its near-zero value is the defining observable in microgravity.
Artificial gravity: A simulated gravity-like effect produced by acceleration, usually rotation. It restores a sustained apparent weight rather than the low apparent weight of microgravity.
Orbital mechanics: The study of motion under gravity, especially the motion of spacecraft and celestial bodies. A spacecraft in orbit continually falls around Earth, creating microgravity conditions.
Parabolic flight: Aircraft flight along repeated parabolic paths that produce brief periods of reduced apparent weight. Aircraft parabolas provide repeated, short microgravity periods without reaching orbit.

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