Standing Waves with Riders

3B22.10

Brief Description

This demonstration, known as Melde’s String or Standing Waves with Riders, illustrates the formation of stationary waves on a wire under tension. By pinching the wire at a specific point, you create a forced node, which constrains the string to vibrate only in frequencies that have a node at that location. Plucking the string provides the energy to excite these specific harmonics. The paper riders serve as visual indicators of the wave's amplitude: those placed at antinodes are thrown off due to the maximum vertical displacement and acceleration of the wire, while those at the node remains undisturbed because that point of the string experiences zero net displacement.

Materials Needed

Two table clamps, four small rods, two pulleys, four 90° clamps, two mass hangers, 10 kg worth of weight, metal wire, and five paper riders.

Materials for Standing Waves with Riders Demo

Set-up

Using two table clamps attach two rods to vertically, using 90° clamps attach the other two rod horizontally to the vertical . Using the final two 90° clamps attach the pulley vertically to the horizontal rod. Bring the metal wire between the two pulleys, and add the mass hangers from each end. Then gradually add 5kg to each hanger carefully. Measure the length between where the wire come in contacts with the pulley, divide that length by six ignorer to determine where to place the riders, and place said riders.

Performing the Demo

The first two riders are removed and and the wire is pinched where the second rider was and then plucked where the first rider was located. the vibration cause third and fifth “riders” to be “bucked” off as they are located at the antinodes and the fourth “rider” rides the wire because it is located at a node.

Someone pinching two points along a wire

A couple folded strips of paper resting on a wire

A strip of paper jumping off a wire

Someone plucking a wire

Safety and Other Notes

The wire is under a lot of tension to the mass. The wire can be a hazard and can cause injury if it breaks. Be careful not to let the masses fall off the setup. Make sure all the rods are secured so that the mass of the wire do not cause the rods to shift.