The Crookes Radiometer from RVFM demonstrates the conversion of radiant energy into mechanical energy.
Consists of a partly evacuated glass bulb approximately 70mm diameter with a fine pivot on which a rotor, having a set of four mica vanes, is delicately balanced
Each vane has one side painted matt black with other side bright
On exposure to sunlight, or a sufficiently bright incandescent light source, the vanes turn
The absorption of radiant energy by the blackened side of the vanes sets up a temperature differential with respect to the bright sides, causing net force to be exerted by the air molecules on the blackened side which makes the vanes rotate with their bright faces leading