|FIELD: Physical Science||DURATION: 45 min.|
|OBJECTIVE: Students will observe the effects of different volumes of air on the amplification of a sound.|
|METHOD: Students observe the loudness of a tuning fork while varying the volume of a container amplifying it.|
|KEY VOCABULARY: Sound wave, amplification, loudness.||GROUP SIZE: Any|
Sound waves travel through the air from where they are created, such as a by school bell, clapping hands, or tuning fork, to our ears where we hear them as sounds (or noises). Oscillating sound waves are created by musical instruments or anything with a steady tone.
We can describe oscillating sound waves pretty well with two main qualities: frequency and wavelength, or the pitch and the 'shape'. Frequency is the pitch of the sound and wavelength is the physical length of one full cycle of the wave. All sound waves travel at the same speed in the same air (approximately 340 meters per second).
Because oscillating sound waves have a particular shape, they will fit well into spaces that have the same shape. The wavelength of the sound wave determines the shape. The better the fit, the louder the sound. A cello is a large instrument because low notes fit better inside it and thus will be naturally louder for deep sounds. A violin on the other hand is much smaller and can generally produce louder, richer high notes.
We can amplify any sounds by providing a space they fit well in. The sound wave from an "A" tuning fork has a very particular wavelength: 77 cm (30 in). It will sound loudest being played into this length container.
In this activity you will find the shape of the sound waves created by an "A" tuning fork by listening for loudness. When the length of the tube equals the wavelength or half the wavelength of the wave, you'll here the loudest amplification.
MATERIALS (per group):