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A drop tower is an experimental facility that releases an instrumented package into free fall, providing a short interval of microgravity. The package and its contents accelerate together, greatly reducing the support forces that normally produce apparent weight. Gravity remains present. Evacuating the drop tube reduces air resistance and the resulting disturbance of the falling experiment.^[ref]

For release from rest through height $h$ with nearly constant gravitational acceleration $g$, $h=g{t}^2/2$, so $t=\sqrt{2h/g}$. A $132$-metre fall gives about $5.19$ seconds in this ideal model, consistent with the facility's reported $5.18$-second test interval. Such experiments reveal how surface tension, fluid flow and combustion behave when gravity-driven effects are suppressed.^[ref]

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]

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.