Sound: How we hear things
Objectives:
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Know that sound is made by something vibrating
Understand how sound travels
Recognise that sound is fainter as distance from the source increases
Plenary
Demonstrate plucking a guitar string to make a sound. Ask the pupils to watch the string
carefully and ask what happens. They should be able to say that it moves slightly and may be
able to name the movements as vibrations. Show the pupils that when the string is made to
stop vibrating, the sound stops suddenly.
Sources of Sound
Explain that sound is created when something vibrates quickly. Ask whether any pupils have
experienced a room vibrating when very loud music is playing.
Pupils must note:
Sound is made when something causes vibrations.
Using the worksheet, pupils should practice identifying where sound may originate from.
Pupils do not need to use or learn the technical names for any of the vibrating parts. They
should colour in: the strings (banjo), the pan (steel pan), the diaphragm (loudspeaker), the
tines (mbira) and the throat/vocal chords (singer).
How sound travels
Ask students how we can hear a guitar string vibrating on the other side of the room. Pupils
should suggest that sound has to travel across the room. Sound needs a medium to travel in.
This medium could be water, a wall, but often it is simply air. If there is no air, such as in
space, no sound can travel. (If equipment is available, demonstrate this by placing an alarm
inside a vacuum jar and removed all the air).
Pupils must note:
We hear sound when vibrations travel through a medium.
You can hear a guitar string on the other side of the room but not on the other side of a
football pitch. Why is that? Pupils should state that it is because the source is too far away.
Ask how else you can make a sound quieter. Pupils may propose covering up your ears or
covering up the sound source.
EXPERIMENT: Introduce a decibel metre to the class, explaining that it measures how loud
sound is. Start an alarm clock ringing, and have a pupil walk slowly away from the decibel
metre. Another pupil should record the volume of the alarm clock in decibels.
OR
EXPERIMENT: Provide a range of materials, such as paper, cotton wool, tissue and
cardboard. Students work in groups to design the best sound-proofing for a ringing alarm
clock. When all designs have been completed, wrap the alarm clock in each group’s design
and gauge volume with a decibel metre.
Pupils must note:
Sound gets quieter at a greater distance from the source.
Pupils may note:
You can make a sound quieter by muffling the source.
Possible extra-curricular questions
How do electronic devices make sound?
A speaker that plays music will have a diaphragm that moves back and forth rapidly to create
sound. Headphones work in the same way, on a much smaller scale.
Why can’t you hear sound when there is no air/in space?
Sound travels due to the vibration of air molecules. In a vacuum like space, there are no
molecules to be moved by vibrations, so sound cannot travel.