Purpose: To demonstrate that the vector sum of the forces on a body in equilibrium is zero.

A board mounted vertically, and having pulleys attached so that forces can be exerted on a metal ring at any desired angle. Angles are indicated on a coordinate system on the board.

After hanging a thread and weight holder over each of the three pulleys, add weights until the metal ring is in equilibrium at the center of the board. Treating two of the weights as known, and using the measured angles, calculate the third weight. Compare with the experimental value. If desired, repeat using different angles.

References: