Standing waves on a spring.

This demonstration shows how standing waves on a spring can be generated by having two people simulate boundary conditions. If one person holds the end of the spring at rest while the other drives the opposite end in an up and down motion, the spring will begin to oscillate. By having the person driving the spring adjust her rate of motion, she will eventually find a rate of motion that produces a single standing wave on the spring. This rate is the fundamental frequency, and it is dependent upon the tension in the spring as well as the spring’s mass per unit length. The fundamental frequency can be measured by timing the up and down motion of the standing wave for 20 cycles and dividing 20 by the recorded time, giving you the fundamental frequency in cycles per second. Other harmonics of the spring can be produced by increasing the driving rate to integer multiples of the fundamental frequency.