TOPIC:

ID Code: C6-17
Purpose: Demonstrate how pulling angle affects the frictional force
Description: A wooden board of weight w, lying on a sandpaper surface, is pulled at an angle a by a string connected to a spring scale. The force F required to move the board is given by: F = w / [ (1/u)cos(a) + sin(a)]. Differentiating F with respect to a, the minimum force is seen to occur at the angle of repose, u=tana. Pulling horizontally is definitely not the most efficient angle!

Pull horizontally to determine u, then check the angle of repose by tilting the sandpaper surface. Then pull at a variety of angles to demonstrate that pulling at the angle of repose requires the least force.

Availability: Available