Name: Speed of Sound Waves in Solids and Liquids
Uploaded: 2019-07-19
Duration: 6 min 40 s
Description: This video enables students to understand the dependence of the speed of sound on the medium properties like young modulus or bulk modulus and density.

Question

A drummer strikes the horizontal surface of a drum so that a sound wave travels upwards from the surface of the drum. Describe how molecules of the air above the drum will move as the sound wave travels upwards. It may help to include a simple diagram.

Accepted Answer

The drum is a percussion instrument. When we strike at the membrane (or skin) of a drum, it vibrates to produce sound. Thus, the sound is produced when the stretched membrane (or skin) of a drum vibrates. Sounds are made by vibrations. When something moves back and forwards many times, we say it vibrates. When the stretched membrane of the drum vibrates, the air around it vibrates. These vibrations in the air travel to our ears. We detect this as sound. When a sound wave passes through the air, the layers in the medium are alternately pushed and pulled. Thus, the particles of the medium move to and fro along the direction of propagation. Therefore, sound waves in the air are longitudinal. The region where particles in a longitudinal wave are closer together is called compression. The region where particles in a longitudinal wave are further apart is called rarefaction. Thus, we can conclude that, when the drummer strikes the horizontal surface of a drum, the membrane vibrates and the surrounding air molecules also vibrate. Alternate compressions and rarefactions are produced and a sound wave is generated. This is indicated in the following figure.

A drummer strikes the horizontal surface of a drum so that a sound wave travels upwards from the surface of the drum. Describe how molecules of the air above the drum will move as the sound wave travels upwards. It may help to include a simple diagram.

Important Questions on Sound

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