 Clinostat

A clinostat rotates a biological specimen so that the direction of gravity changes continuously relative to it. A horizontal rotation axis is commonly used in experiments on plant gravitropism. Rotation changes the history of directional stimulation; it does not switch off the gravitational field.

For an ideal specimen rotating at angular speed $\omega$, a body-fixed representation can be $\mathbf{g}(t)=g(0,\cos \omega t,\sin \omega t)$. Its average over a full turn is zero, but $|\mathbf{g}(t)|=g$ throughout. A sufficiently slow biological response might integrate the changing directions, while a faster response can distinguish them. A vertical-axis control does not produce the same change in gravity direction relative to the specimen.

Rotation also introduces an acceleration scale $a={\omega }^{2}r$ at distance $r$ from the axis. At $r=1\mathrm{cm}$, one revolution per minute gives approximately $1.1\times 10^{-4}m/{\mathrm{s}}^2$, while sixty revolutions per minute gives about $0.39m/{\mathrm{s}}^2$. These are illustrative kinematic calculations, not recommended operating speeds. Moving a specimen farther from the axis also changes this acceleration.

A 1976 experiment combined clinostat rotation with centrifugation. Several developmental outcomes still depended on the applied acceleration, demonstrating incomplete gravity compensation.^[ref] This motivates comparing orientation history, rotation effects and genuine reduced-gravity conditions rather than labelling every rotating preparation weightless.