The inclined plane is a simple machine with which Galileo designed a series of experiments to demonstrate the law of falling bodies. The apparatus is also suitable for studying equilibrium conditions and the attrition of bodies resting on surfaces sloped at different angles.

The Museum possesses two specimens of late-eighteenth-century planes with variable inclination, based on the same operating principle.

Apparatuses of this kind typically consist of a base hinged to a frame holding a highly polished plane that minimizes attrition. The plane's angle to the horizontal is set by means of two arc-shaped guides. The top of the frame carries a square-section bar fitted with a pulley. A string passing through the pulley is tied, at one end, to the brass cylinder resting on the plane and, at the other end, to a counterweight that hangs vertically.

By changing the slope of the plane and applying different counterweights to the cylinder, one can test the changes in the equilibrium conditions and in the cylinder's attrition on the plane.