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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. Sound travels because the vibrating object makes nearby particles vibrate. Sound needs a medium to travel through – it cannot pass through a vacuum.

Good vibrations! What vibrates so that each of these objects makes sound? drum skin mouth blowing horn lute strings harp strings 4

How does sound travel through the air? Teacher Notes You should point out to your class that in fact, the air particles would be constantly moving around randomly. In the animation, they are only moving a little so that the change in density as the wave moves is more obvious.

‘Seeing’ sound waves speaker oscilloscope If we connect an mp3 player to a speaker, we can all hear the sound produced. If we also connect an oscilloscope to the mp3 player then we can ‘see’ the sound waves. 6

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.

Pitch and frequency A sound can be high or low – this is the pitch of the sound. low pitch high pitch 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 frequency of the waves on the trace, the lower/higher the pitch.

Which wave is the loudest and highest? Which trace represents the loudest sound? A B Sound A has the largest amplitude (i.e. the tallest waves), so it is the loudest of these two sounds. Which trace represents the sound with the highest pitch? A B Sound B has the greater number of waves across the oscilloscope – it has the highest frequency and so has the highest pitch.

Amplitude and wavelength

Describing sound waves

Sound waves summary

Speed of sound – experiment This investigation for calculating the speed of sound should be carried out in a quiet open space. One student should hold a stopwatch, whilst another should be holding some cymbals 100 metres away. 100 m When you see the cymbals crash, press start. When you hear the cymbals crash, press stop.

Speed of sound – results Record the results of the sound experiment in a table like this: Experiment Distance (m) Time (s) Speed (m/s) 1 100 0.34 294 2 3 4 How are these values used to estimate the speed of sound? Teacher notes In order to more accurately calculate the speed of sound, this experiment should be repeated a number of times. speed = distance time = 100 0.34 294 m/s 15

Speed of sound – analysis The first cymbal experiment gives an estimate for the speed of sound as 294 m/s. Use the average of your results to calculate another estimate for the 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 sound in air?

Energy transfer How many different energy transfers do you think take place during this experiment? When the cymbals crash there is a transfer of kinetic energy from the cymbals to the air particles. When the sound waves reach the ear, there is a transfer of kinetic energy from the air particles to the eardrum. kinetic energy of cymbals kinetic energy of air particles kinetic energy in eardrum

Sound in different materials Sound needs a substance through which to travel because it travels by making particles vibrate. Which state of matter does sound travel fastest through? Sound waves travel fastest through solids. The particles in a solid are closer together than in a gas, and more tightly bound than in a liquid. This means vibrations are more easily passed from particle to particle, and so sound travels faster. 18

Sound waves in different materials

Speed of sound in different materials

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 5 120 jet fighter 900 2 450 cheetah 50 2.5 20 meteorite 10,000 0.35 28,571.4 The jet fighter and the meteorite travel faster than the speed of sound in air. This is called breaking the sound barrier. Photo credit: © 2008 Jupiterimages Corporation 21

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.

Investigating echoes Plan an investigation to measure the speed of sound using echoes. You may use any of the following equipment: stopwatch clapper board Worksheet 1 accompanies this slide. The worksheet guides students through designing and analysing this experiment. starting pistol hard, flat surface Remember to make sure it is a fair test. 24

Analysing your results Calculate the speed of sound for each of your distances using the formula below. distance speed = time How do your calculations compare with the actual speed of sound in air? Which of your distances gave the most accurate answer? Were there any errors in your experiment? Could you improve the experiment in any way to make it even more accurate? 25

How do we hear?

How does the ear work? 1. Sound waves are collected by the outer ear (or pinna). 6.The auditory nerve takes the signals to the brain. 4. The small bones (ossicles) amplify the vibrations. 3. The waves reach the eardrum and make it vibrate. 2. The waves travel along the ear canal. 5. The cochlea turns these into electrical signals. Worksheet 2 accompanies this slide. The worksheet tests students’ memory skills and understanding of how the ear works. 28

The ear and hearing summary

What range of frequencies can you hear? Humans can only hear sounds of certain frequencies. The range of frequencies a person can hear is called their hearing range. Hearing range can be tested using a pitch sweep, in which the frequency of a sound wave is gradually increased. This can be created using a signal generator and loudspeaker. What is the hearing range of a healthy young person? 20 Hz to 20,000 Hz

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. Photo credit: © 2008 Jupiterimages Corporation 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. 31

Hearing ranges As we get older, our ability to hear high pitched sounds deteriorates. Some shopkeepers use this to their advantage. A device has been developed called a ‘Mosquito’ which emits sounds of around 20,000 Hz. This is audible, and potentially quite annoying, for teenagers who may be loitering around the shop, but is not noticeable to older customers. Some human rights groups have claimed that the devices demonise young people indiscriminately. Others claim they are a cheap, non-violent way to deal with troublesome yobs. What do you think? 32

Should ‘Mosquitoes’ be banned?

Animals’ hearing ranges

Ordering volumes

Reducing noise 36

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