Download Sound: Properties of sound

Sound: Properties of sound
Objectives:
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Find patterns between the pitch of a sound and features of the object that produced it
Find patterns between the volume of a sound and the strength of the vibrations that
produced it
Plenary
Explain that in wind instruments, sound is made by air vibrating within the tube. Show the
pupils short clips of wind instruments being played and ask them how they sound different.
They may be familiar with the concept of pitch and be able to state that the smaller
instruments are higher pitched than the larger ones.
Pitch of Sound
EXPERIMENT: Provide pupils with empty bottles and jugs of water. Explain that in wind
instruments, the air inside the tube is made to vibrate. The length of the tube (bottle) in this
experiment is adjusted by filling the bottom with water. A sound will be made by blowing
over the top of the bottle. Pupils should investigate what happens when more water is poured
into the bottle and report back with their findings. They should find that when the tube is
shorter (bottle is fuller), the pitch is higher.
OR
EXPERIMENT: Provide pupils with different types of rubber bands. Liken the rubber bands
to the strings of an instrument, or to vocal chords in a singer’s throat. Encourage the pupils to
try stretching the rubber bands to different tensions and plucking them. Pupils should discuss
how the pitch of the sound is affected; the tighter the band is stretched, the higher the pitch.
Pupils must note:
By changing the sound source, the pitch of the sound can be changed.
Pupils may note:
A tight string makes a higher pitched sound than a loose string. A short column of air makes a
higher pitched sound than a long column of air.
Volume of Sound
Play a cymbal or guitar quietly and then more loudly. Ask the students how the vibrations
may be different. The vibrations are stronger when the instrument is played more loudly.
Demonstrate that the vibrations can be limited and hence the sound can be made quieter by
touching the vibrating part. Pupils do not need to know about damping, only to recognise that
the size of the vibrations correlate with the volume of the instrument.
ACTIVITY: Play Simon Says with directions such as ‘make a sound with small vibrations’,
‘make a sound with a low pitch’ or ‘make a sound with strong vibrations and a high pitch’.
Pupils may drum on tables, clap their hands or use their voices.
Pupils must note:
A loud sound has stronger vibrations than a quiet sound.
Possible extra-curricular questions
What are the highest and lowest pitches that humans can hear?
From 20Hz (20 vibrations every second, about the pitch of a tiger’s roar) to 20kHz (20,000
vibrations every second, about the pitch of the ‘mosquito’ noise).
If sound is due to vibrations, can we feel sound?
Yes. It is easy to touch an instrument and feel it vibrating. When loud music plays in a room,
you can feel the room ‘tremble’. We can feel but not hear very low pitched sounds (the study
of very low pitched sound is called infrasonics.)
Why can young people hear higher pitched sounds than adults?
As we get older, our hearing range degrades; adults are worse at detecting high pitched
noises. The process is called presbycusis and is natural; it simply involves hair cells in our
ears dying.
Why does hearing loud noises make you deaf?
When a loud noise enters your ear, the hair cells in your ear become over-stimulated and so
your body delivers oxygen to your ear. This causes cells to die (oxidative cell death) and
early loss of hearing.