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Understanding Sound Waves

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Understanding Sound Waves

Oliver and Ruben are helping at a vet clinic during a busy afternoon. They notice that a quiet beep, a dog’s bark and a tuning fork all make sounds in different ways. Use the information and diagrams on this sheet to investigate how sound waves work. Answer every question; show your working for calculations.

What sound needs

Sound begins when an object vibrates. The vibration makes particles in a material medium (such as air, water or metal) vibrate back and forth. This disturbance transfers energy through the medium as a longitudinal wave. Sound cannot travel through a vacuum because there are no particles to carry the vibration. In air, crowded particles form compressions and more spread-out particles form rarefactions.

1.Oliver taps a tuning fork beside a sealed container from which most of the air has been removed. The sound becomes much fainter. Choose the best explanation.

Sound needs particles in a medium to transfer its energy.
Sound travels only through liquids.
The tuning fork has stopped vibrating because the container is sealed.
Sound is an electromagnetic wave.

2.A sound wave moves through air. Decide whether each statement is true or false: (a) air particles travel all the way from the source to the listener; (b) the particles vibrate back and forth as energy moves through the air.

TrueFalse

3.A clinic doorbell sends sound through air, while a vibration from a machine can travel through its metal casing. Name the material in each example that acts as the medium.

Reading wave patterns

Frequency is the number of complete vibrations each second, measured in hertz (Hz). A higher frequency is heard as a higher pitch. Amplitude describes the size of the vibration; a larger amplitude is heard as a louder sound. For the same sound medium, a higher frequency also corresponds to a shorter wavelength.

Trace A /\ /\ _____/ \_____/ \_____ Two complete cycles; small height

Trace B /\ /\ /\ /\ ___/ \__/ \__/ \__/ \___ Four complete cycles; greater height

4.Compare Trace A and Trace B. Which trace represents the higher pitch, and which represents the louder sound? Explain using frequency and amplitude.

5.A tuning fork vibrates 440 times each second. What is its frequency, and what does that value mean?

6.Complete the links: (a) increasing amplitude makes a sound ; (b) increasing frequency makes its pitch .

7.A high-pitched beep and a low, rumbling sound are played at the clinic. Which one has the higher frequency? Explain how you know.

Sound in action

The speed of sound depends on the medium and conditions. It generally travels faster in solids than in liquids, and faster in liquids than in gases. In air at about 20°C, its speed is approximately 340 metres per second.

8.Ruben hears a metal trolley rattle through its metal frame as well as through the air. In which material would sound generally travel faster: the metal frame or the air?

The metal frame
The air
At the same speed in both
Sound cannot travel through metal

9.During a storm, Oliver sees a flash and hears thunder 5 seconds later. Using 340 m/s for the speed of sound, estimate how far away the storm is. Show the calculation and give the distance in kilometres.

10.The clinic uses an ultrasound scanner to make images inside an animal’s body. Ultrasound is sound with a frequency higher than humans can hear. Explain why ultrasound is still a sound wave, and identify one thing it needs in order to travel through the body.

11.A siren on a moving vehicle sounds higher-pitched as it approaches and lower-pitched as it moves away. In your own words, explain how the spacing of the sound waves reaching a listener changes and link this to pitch.