# KS3 Physics 8L Sound and Hearing.

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KS3 Physics 8L Sound and Hearing

8L Sound and Hearing What is sound? Speed of sound Reflecting sound
Contents 8L Sound and Hearing What is sound? Speed of sound Reflecting sound The ear and hearing Summary activities

Sounds are made when an object vibrates.
What causes sound? Take a tuning fork and strike it against a block of wood. What do you observe? The tuning fork vibrates and you hear a sound. Sounds are made when an object vibrates.

Good vibrations! What vibrates so that the following make sounds?
violin strings drum skin voice box loudspeaker cone

The bell-jar experiment
Place a ringing clock inside the bell jar and what happens? There is air inside the bell jar so the sound can travel and be heard. vacuum pump on Remove the air from the bell jar and what happens to the sound? The sound cannot be heard because there is no air inside the bell jar (a vacuum).

Studying sound waves Sound waves can be studied with this type of equipment. loudspeaker oscilloscope signal generator A loudspeaker converts signals from the signal generator into sound waves. An oscilloscope shows wave patterns and allows us to ‘see’ sound. A signal generator produces different types of signals.

Loudness and amplitude
A sound can be quiet or loud. quiet sound loud sound On an oscilloscope trace, the loudness of a sound is shown by the height of the wave. This is called the amplitude. Which word should be crossed out in this sentence? The larger the amplitude of the wave on the trace, the louder/quieter the sound.

Which is the loudest? A B Which trace represents the loudest sound?
Sound A is the loudest. Sound A has the largest amplitude (i.e. the tallest waves), so it is the loudest of these two sounds.

low pitch sound high pitch sound
Pitch and frequency A sound can be high or low – this is the pitch of the sound. low pitch sound high pitch sound On an oscilloscope trace, the pitch of a sound is shown by how many waves there are. This is called the frequency. Which word should be crossed out in this sentence? The greater the number of waves across the oscilloscope trace, the lower/higher the frequency and pitch.

Which is the highest? Which trace represents the sound with the highest pitch? A B Sound B is the highest pitched. Sound B has the most number of waves across the oscilloscope – it has the highest frequency and so has the highest pitch.

Wave animation

8L Sound and Hearing What is sound? Speed of sound Reflecting sound
Contents 8L Sound and Hearing What is sound? Speed of sound Reflecting sound The ear and hearing Summary activities

Speed of sound experiment
This investigation to calculate the speed of sound should be carried out in a quiet open space. START STOP 100 m 1. When you see the cymbals crash, press START. 2. When you hear the cymbals crash, press STOP.

Speed of sound experiment – results table
Record the results of the sound experiment. Experiment distance (m) time (s) speed (m/s) 1 2 3 4 100 0.34 294 How are these values used to estimate the speed of sound? distance time speed = = 100 0.34 = 294 m/s

Speed of sound experiment – results
The speed of sound in air is about… 340 m/s Use the results of the cymbals experiment to calculate the average speed of sound. How does this calculation for the average speed of sound compare with the real speed? What errors could have affected the results of the cymbals experiment? Do you think the speed of sound in water is the same as the speed of in air?

Sound in different states of matter
Sound needs a substance to travel through and travels by particles vibrating. Which state of matter does sound travel fastest through? solid liquid gas Sound waves travel fastest through solids. The particles in a solid are closer together than in a gas or a liquid. This means vibrations are more easily passed from particle to particle and so sound travels faster.

Speed of sound in different materials
Sound need particles to travel and the type of substance affects the speed of sound. speed of sound (m/s)

Breaking the sound barrier!
Which of these travel faster than the speed of sound in air? distance (m) time (s) speed (m/s) small aeroplane 600 5 jet fighter 900 2 cheetah 50 2.5 meteorite 10 000 0.35 120 450 20 28,571 The jet fighter and the meteorite travel faster than the speed of sound in air – this is called breaking the sound barrier.

Sound or light – which is faster?
During a thunderstorm, thunder and lightning are created at the same time. Which do you notice first? Usually, you see lightning before you hear thunder. Light travels much faster than sound. 300,000,000 m/s The speed of light is… How much faster is light than sound? How could you use thunder and the speed of sound to estimate how far away a thunderstorm is?

8L Sound and Hearing What is sound? Speed of sound Reflecting sound
Contents 8L Sound and Hearing What is sound? Speed of sound Reflecting sound The ear and hearing Summary activities

Reflected sound What happens when a sound wave meets a hard flat surface? The sound wave is reflected back from the surface. This is called an echo.

Echo experiment START STOP
Stand at least 100 m from a large, flat wall with a stop watch. START 150 m STOP 1. Use a starting pistol (or clapper board) to make a sound. 2. Measure the time taken between firing the pistol and hearing the echo.

Echo experiment distance time speed = = 300 0.92 = 326 m/s
The sound of the starting pistol takes 0.92 s to travel a distance of 300 m. How can you use this result to estimate the speed of sound? distance time speed = = 300 0.92 = 326 m/s Repeat the experiment several times to obtain an average. How does your calculation for the average speed of sound compare with the real value? compare with the real value?

Questions on reflecting sound
1. What is a reflected sound called? an echo 2. Are hard or soft surfaces best at reflecting sound? hard surfaces 3. Why are there soft materials on the walls of cinemas and theatres? to reduce echoes 4. Name two animals that use echoes for navigation or communication. bats and dolphins

8L Sound and Hearing What is sound? Speed of sound Reflecting sound
Contents 8L Sound and Hearing What is sound? Speed of sound Reflecting sound The ear and hearing Summary activities

The ear and sound waves

How does the ear hear? 1.Sound waves are collected by the ear lobe or pinna. 6.The auditory nerve takes the signals to the brain. 6 4 1 2 3 5 2.The waves travel along the ear canal. 5.The cochlea turns these into electrical signals. 3.The waves make the ear drum vibrate. 4.The small bones (ossicles) amplify the vibrations.

Hearing range Set the volume and increase the frequency of the signal provided by the signal generator. Humans can only hear sounds of certain frequencies. The range of frequencies a person can hear is called their hearing range. What is the hearing range of a healthy young person? 20 Hz to 20,000 Hz

Comparing hearing ranges
Which animals hear the lowest and the highest frequencies? 100,000 10,000 1,000 100 10 1 frequency (Hz) Frequency low (Hz) high (Hz) Human Dog Bat Elephant Mouse Cat Dolphin human dog bat elephant mouse dolphin

Hearing ranges and hearing loss
Does everyone have the same hearing range? We all have slightly different hearing ranges People lose the ability to hear sounds of high frequency as they get older. Almost 1 in 5 people suffer some sort of hearing loss. Temporary hearing loss may be caused by ear infections and colds, after which hearing recovers. Permanent hearing loss and deafness can be present at birth or occur if the ear is damaged or diseased.

Measuring loudness – the decibel scale
160 140 120 100 80 60 40 20 personal stereo permanent ear damage aircraft overhead loud bell circular saw at 2m quiet countryside pin being dropped can just be heard

3. putting noisy machinery in insulated rooms
Noise and its effects A noise is any unwanted sound. What one person considers noise another person might not. Can you name any examples? Noise can cause hearing problems. List three effects of noise. 1. headaches 2. nausea 3. deafness List three ways of reducing the effects of loud noise. 1. ear protectors 2. double glazing 3. putting noisy machinery in insulated rooms

8L Sound and Hearing What is sound? Speed of sound Reflecting sound
Contents 8L Sound and Hearing What is sound? Speed of sound Reflecting sound The ear and hearing Summary activities

amplitude – The height of a wave, which shows how loud
Glossary amplitude – The height of a wave, which shows how loud a sound is. cochlea – The part of the inner ear that changes vibrations into electrical signals which are then sent to the brain. decibel – The unit for measuring the loudness of sound (dB). eardrum – The thin membrane in the ear which vibrates when sound reaches it. frequency – The number of waves per second, which shows the pitch of a sound. hertz – The unit of frequency (Hz). 1 Hz = 1 wave per second. oscilloscope – An instrument that shows a picture of sound. pitch – How high or low a sound is. sound – A form of energy produced by vibrations, which is detected by the ears.

Anagrams

Multiple-choice quiz