Physics Dept. Demonstration Manual

DS16 - Hammer on Hinged Board

  • To illustrate the center of mass.
  • Stand
  • 3 finger clamp
  • Hinged board
  • Hammer and thread

Method and Theory:

First, clamp the hinged board to the stand so that the hinge is on the underside of the board. Observe what happens to the outer board. Since its center of mass is outside the hinge, gravity creates a net torque on the board, which causes it to swing downward. Now strap the hammer to the outer board so that the head of the hammer hangs below the clamped board. As the center of mass of the hammer is brought further and further beneath the clamped board, a situation is reached in which the combined center of mass of the outer board and the hammer is on the inner side of the hinge. Gravity, therefore, acts on this combined center of mass to create a net torque upward on the board.

The demonstration takes about 1 minute to perform.

( Thanks to Pam Borman for suggesting this demo )