# Explore the Properties of Sound Waves

In this worksheet, students will look at the definitions of intensity, amplitude, pitch and frequency and also at sound as a wave and vibration.

Key stage:  KS 3

Curriculum topic:   Physics: Waves

Curriculum subtopic:   Energy Waves

Difficulty level:

#### Worksheet Overview

What makes sound?

Sound is a form of energy, and hearing is one of our most important senses. The sounds we hear vary in intensity from quiet to loud.  Sounds can also have a high or low pitch.

Sound energy makes objects vibrate - for example, vocal chords in the throat when we speak and guitar strings.  Different musical instruments are designed to make different sound waves.  Musicians use tuning forks to find a note by tapping the fork lightly so that it makes a pure sound - the two prongs vibrate to make a note.  Here is a picture of a tuning fork:

Properties of sound waves

Sound is what we call a pressure wave, also known as longitudinal waves. Sound waves carry energy parallel to the direction of the wave. We can view the way sound waves travel by using a slinky spring (see picture below). Vibrations are created when we push and pull one end of the slinky backwards and forwards. When sound travels through the air, the air particles squash up (compressions - areas of high pressure) and then move apart (rarefactions - areas of low pressure) just like the coils of the slinky.

The frequency of a wave is the number of complete waves that pass through a fixed point in a second. Frequency is measured in Hertz (Hz). Listening to a 20 Hz sound means 20 sound waves reach your ear every second. The pitch of a sound depends on the frequency, so high-pitched sounds have a high frequency and low-pitched sounds have a low frequency.

The distance between the tops of two waves as shown in the oscilloscope is called the wavelength. A long wavelength means the sound has a low frequency and a low pitch, whereas a short wavelength means high frequency and high pitch. Half the height of a wave is called the amplitude. Bigger amplitude means the sound has more energy and is louder than a sound with a smaller amplitude.

Wavelength, frequency, and speed

The diagram below illustrates the wavelength and amplitude of a wave on an oscilloscope screen:

Remember, sound itself is a longitudinal wave, not a transverse wave as shown above. Therefore, if you actually examined a sound wave, the wavelength would be the distance between two compressions or two rarefactions of the particles it is forcing to vibrate, while amplitude would be the maximum distance each particle would be from its equilibrium position. The graphs obtained from oscilloscopes make it easier to visualise and measure these values.

The frequency of a sound wave, measured in Hertz (Hz) is the number of times it vibrates every second. For example, a sound wave with a frequency of 1,000 Hz vibrates 1,000 times every second.

The speed of sound in air is around 330 metres per second. Assuming this remains constant, increasing the frequency of a sound wave decreases the wavelength (and vice versa).

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