Propagation of sound in air

Principle

This experiment demonstrates, particularly clearly, the propagation of sound waves in air and, thereby, the working principle of the eardrum that is caused to oscillate by pressure waves. The movement of the membrane is transferred to the neighbouring air molecules, which in turn transfer it to their respective neighbouring molecules. All of the molecules oscillate around their position of rest, since - just like springs - they are joined by cohesive forces. This leads to pressure variations that propagate through space in the form of a sound wave (pressure wave). If a second drum is held precisely in parallel to the first one, the wave can cause the membrane of the drum to oscillate.

Benefits

• Experiment is part of an experiment set with a total of 22 experiments about generation, propagation and perception of sound, oscillations and waves
• Particularly appropriate as an experiment for first contact with physics in general
• With graphic student worksheets
• With detailed instructor information
• Optimized for tight schedules, i.e. minimum preparation time required

Tasks

The sound is generated by striking a frame drum or the bottom of a tray vigorously with a striking hammer. The "sound receiver" is a (second) frame drum. Its movement is visualised with the aid of a styrofoamsphere pendulum. Try this method of detection out and try to optimise it.

Learning objectives

• Sound waves
• Eardrum
• Oscillations