Answer to Question #184141 in Physics for John

Question

Explain the term resonance in terms of natural frequency and forced vibrations. Illustrate your answer with a description of the demonstration of Barton’s pendulums

Answer 1

Forced vibrations can also show another very important effect. With the swing you will find that if you push in time with the natural frequency of the swing then the oscillations build up rapidly. This last fact is an example of resonance.

All systems have their own natural frequency, and if you apply a driving force of the same frequency and in phase with the initial oscillations then resonance results, the amplitude of the oscillations gets larger and larger. Parts of a car may vibrate if you drive over a bumpy road at a speed where the vibrations transmitted to the body are at the resonant frequency of that apart. (Actually cars are designed not to do this by choosing parts with natural frequencies that are not likely to be produced by driving). Bass frequencies from stereo speakers can make a room resonate, particularly annoying if you live next door and your living room resonates due to your neighbour's music!

Barton's pendulums are a very good way of demonstrating forced vibrations and resonance in the laboratory. A heavy driving pendulum X is hung from a thread fixed to a cord between two retort stands. Hanging from the cord are five other pendulums, each with a light paper cone as the bob.