The simulation of microgravity depends on a variety of factors, the response time, external factors such as buoyancy, temperature, light etc. If the(gravi)stimulus changes constantly and faster than the response time, the (biological) system is unable to respond to the stimulus. However, the compensation of gravity by rotation must be limited to avoid centrifugal forces that may result in unrelated effects on the system of interest. The figure below illustrates the constraints of rotational simulation. Assuming that the axis of rotation is horizontal, the lines give the limit of the centrifugal force induced by the angular velocity ω (omega) as a function of the radius. As the radius increases the centrifugal force increases and the size of the system becomes a limiting factor. The response time determines the minimal rotational speed (angular velocity). For plants the response (presentation) time is about 1-2 minutes. Because the system integrates the rotation over time, the stimulus in one direction must be less than the time needed for one half revolution. In our example, a plant with a one-minute response time needs to be rotated faster than one half revolution per minute (~0.05 radians per second).

Log/log plot of radius and angular velocity. the different lines define the various g-levels by the centrifugal force. The rectangles exemplify usable radius and velocity ranges for slow (yellow) and fast (pink) clinostats.

Therefore typical (slow-rotating) clinostats turn at a rate of 1 to 2 rpm. The physical dimension of the plant (e.g. leaf length) must be less than the predetermined threshold of centrifugation. For a plant with 5 cm long leaves the yellow box describes the usable operating range of a clinostat.

In contrast, the so-called fast rotating clinostats operate at rates of 30 to 150 rpm but are restricted in diameter (purple rectangle). These clinostats are often used with liquid systems (algal suspensions), where sedimentation is compensated by faster rotation while maintaining the ‘normal’ interaction of the organism(s) with the(ir) environment.

Therefore rotation leads to compensation of gravity but not weightlessness (i.e., true microgravity). Because plants sag in response to their own weight, an often underestimated artefact of clinorotation is excessive mechanostimulation.