Microgravity is a condition of very small residual acceleration or apparent weight experienced within an experimental system. An orbiting spacecraft and its freely moving contents fall together under gravity, greatly reducing the support forces experienced on the ground. A drop tower provides a shorter interval using the same free fall principle.[ref]
Zero Gravity Research Facility by NASA. Free-fall microgravity and experimental facility
Residual disturbances include air resistance, vibrations, vehicle manoeuvres and spatial variation in gravitational acceleration. Their importance depends on the experiment's duration and length scale. Suppressing gravity-driven convection or settling lets surface tension, diffusion and other processes become easier to isolate; the result is an experimentally controlled change in dominant forces, rather than removal of the gravitational field.
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