What causes sound? How does sound travel? © cgrahamphysics.com 2016
What causes sound?
How does sound travel?
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Can you guess
the sounds?
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How many did
you guess right?
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Aim
• To explain how sound travels • To use scientific words to describe
sounds
Keywords • Amplitude, frequency, pitch, sound,
cochlea, eardrum, decibel
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Word Meaning
intensity The loudness or volume of a sound. pitch How high or low a note sounds. vibrate Move backwards and forwards. amplitude Half the height of a wave. frequency The number of waves each second. hertz (Hz) The unit for frequency. 1 hertz means one
wave per second. loudness How loud a sound is; the volume of a
sound. oscilloscope An instrument which shows a picture of a
wave on a screen.
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Listen to the tuning fork, what do you observe?
The tuning fork vibrates and you hear a sound.
All sounds are caused by vibrations.
What causes sound?
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• For a sound to travel the vibrations must be passed on
• Sound is produced by a vibration and travels as a longitudinal wave
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How does sound travel through the air?
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If we connect an mp3 player to a speaker, we can all
hear the sound produced.
‘Seeing’ sound waves
If we also connect an oscilloscope to the mp3 player then
we can ‘see’ the sound waves.
speaker oscilloscope
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How sound travels…
1) An object makes a sound by vibrating
2) The vibrations pass through air by making air molecules vibrate
3) These vibrations are picked up by the ear
Air molecules
4) The ear then sends a message to the brain
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Good vibrations!
What vibrates so that each of these objects makes sound?
harp strings
lute strings
drum skin
mouth blowing horn
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Sound waves are vibrations and so need a substance to travel through.
With air inside, the sound can be heard.
With nothing inside [a vacuum], the sound can’t be heard.
What happens when the air is removed from the bell-jar?
Bell Jar Demonstration
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Travelling sound
Sound travels by particles vibrating. To understand this better you need to remember what the particles look like in a solid, liquid and a gas:
Gas Liquid Solid
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Cup Telephones
One person from each group of two should get a telephone from the bench.
Answer in full sentences:
How is the sound being transmitted to your ear?
Can you hear sounds that would be inaudible from a distance?
If so why?
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Making Sound
Sound is caused by __________.
These vibrations make nearby ________ vibrate, which make the molecules next to them vibrate passing the sound along to our _____.
So if there are no particles sound will not travel.
ears, vibrations, molecules © cgrahamphysics.com 2016
Describing Sound Sounds can be quiet or loud.
Sounds can have different pitches (they can be high or low)
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1
2
3
4
5
6
7
8 camel
owl
sealion
monkey
harp
tapdancer
organ
siren
a) What is it? b) Is it high or low pitch
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What Causes Sound? recap
Aim
To explain how sound travels
To use scientific words to describe sounds
Plenary
Write down a small paragraph explaining how sound travels and why it travels differently in solids, liquids, gases and vacuums
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