Parallel Forces/Beam with Two Scales

Brief Description

This physics demonstration illustrates the principles of static equilibrium and the distribution of forces in a rigid body. A uniform wooden is supported at two points by spring scales; which are typically positioned at the ends or symmetrical distances from the center. When weights are placed at various positions along the beam, the sum of the readings on the two scales remains equal to the total weight of the beam and the added loads, satisfying the condition for translational equilibrium (∑F_y = 0). Furthermore, by adjusting the position of the weights, students can observe how the individual scale readings change, demonstrating the principle of rotational equilibrium (∑τ = 0); as a load moves closer to one scale, that scale's reading increases while the other decreases, maintaining a constant total force but reflecting the change in torque relative to each support point.

Materials Needed

Two scales, the wooden beam, three rods with a length of at least 1 meter, two table clamps, two 90° rod clamps, and a mass of two kg.

Set-up

Set up a structure to hang the beam on from using the three rods, table clamps, and the 90° rod clamps. Hang the scales from the horizontal rod and suspend the wooden beam from the scales.

Performing the Demo

Place the 2 kg mass in the middle of the beam to show that the forces felt by the scales are the same, them move the mass around the beam and show that the forces felt by the scales change depending of the placement of the mass. The total forces felt by the scales should remain constant regardless of the location of the mass on the beam.

Safety and Other Notes

Be careful not to let the weight fall off the beam