Generating standing waves from transverse waves on a rope and from longitudinal waves on a slinky spring.
Apparatus and materials
Rope, 6 m, soft and flexible
Tank, large rectangular transparent
Health & Safety and Technical notes
a Tie one end of the rope securely to a fixture on a wall. Pull the other end taut. Move that end up and down, to excite transverse waves. Build up a pattern of standing waves, by feeling for the right resonant frequency, and adjusting the tension.
A more effective method is to drive the motion at a node. Secure the rope firmly at both ends. Mark off the rope into equal segments, such as fifths. Make a loose ring with a finger and thumb round the rope at the nearest marked point. Move your hand up and down, and change the frequency until the 5-loop motion builds up. Different resonances can be produced, of course, by changing the frequency or the tension.
b Build up a longitudinal standing wave on a Slinky. Clamp both ends of the well-stretched spring, support it on a trolley runway, and excite it by hand near a node.
Be clear about the purpose of your demonstration. Depending on the course level and students’ abilities, your purposes in demonstrating standing waves may be any or all of the following:
- to demonstrate standing wave patterns as a form of vibration.
- to discuss energies associated with different patterns.
- to consider the two trains of waves necessary to the production of standing waves.
This experiment was safety-checked in February 2006