28L Sound and Hearing What is sound? Speed of sound Reflecting sound Contents8L Sound and HearingWhat is sound?Speed of soundReflecting soundThe ear and hearingSummary activities
3Sounds 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.
4Good vibrations! What vibrates so that the following make sounds? violin stringsdrum skinvoice boxloudspeaker cone
5The bell-jar experiment Place a ringing clock inside the bell jar and what happens?There is air inside the bell jarso the sound can travel and be heard.vacuumpump onRemove the air from the bell jarand what happens to the sound?The sound cannot be heard because there is no air inside the bell jar (a vacuum).
6Studying sound wavesSound waves can be studied with this type of equipment.loudspeakeroscilloscopesignal generatorA 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.
7Loudness and amplitude A sound can be quiet or loud.quiet soundloud soundOn 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.
8Which 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.
9low pitch sound high pitch sound Pitch and frequencyA sound can be high or low – this is the pitch of the sound.low pitch soundhigh pitch soundOn 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.
10Which is the highest?Which trace represents the sound with the highest pitch?ABSound 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.
128L Sound and Hearing What is sound? Speed of sound Reflecting sound Contents8L Sound and HearingWhat is sound?Speed of soundReflecting soundThe ear and hearingSummary activities
13Speed of sound experiment This investigation to calculate the speed of sound should be carried out in a quiet open space.STARTSTOP100 m1. When you see the cymbals crash, press START.2. When you hear the cymbals crash, press STOP.
14Speed of sound experiment – results table Record the results of the sound experiment.Experimentdistance (m)time(s)speed(m/s)12341000.34294How are these values used to estimate the speed of sound?distancetimespeed ==1000.34=294 m/s
15Speed of sound experiment – results The speed of sound in air is about…340 m/sUse the results of the cymbals experimentto 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?
16Sound 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?solidliquidgasSound 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.
17Speed 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)
18Breaking the sound barrier! Which of these travel faster than the speed of sound in air?distance(m)time(s)speed(m/s)small aeroplane6005jet fighter9002cheetah502.5meteorite10 0000.351204502028,571The jet fighter and the meteorite travel faster than the speedof sound in air – this is called breaking the sound barrier.
19Sound 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/sThe 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?
208L Sound and Hearing What is sound? Speed of sound Reflecting sound Contents8L Sound and HearingWhat is sound?Speed of soundReflecting soundThe ear and hearingSummary activities
21Reflected soundWhat happens when a sound wave meets a hard flat surface?The sound wave is reflected back from the surface.This is called an echo.
22Echo experiment START STOP Stand at least 100 m from a large, flat wall with a stop watch.START150 mSTOP1. Use a starting pistol (or clapper board) to make a sound.2. Measure the time taken between firing the pistol andhearing the echo.
23Echo experiment distance time speed = = 300 0.92 = 326 m/s The sound of the starting pistol takes 0.92 sto travel a distance of 300 m.How can you use this result to estimate the speed of sound?distancetimespeed ==3000.92=326 m/sRepeat 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?
24Questions on reflecting sound 1. What is a reflected sound called?an echo2. Are hard or soft surfaces best at reflecting sound?hard surfaces3. Why are there soft materials on the walls of cinemas and theatres?to reduce echoes4. Name two animals that use echoes for navigation or communication.bats and dolphins
258L Sound and Hearing What is sound? Speed of sound Reflecting sound Contents8L Sound and HearingWhat is sound?Speed of soundReflecting soundThe ear and hearingSummary activities
27How does the ear hear?1.Sound waves are collected by the ear lobe or pinna.6.The auditory nervetakes the signalsto the brain.6412352.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.
28Hearing rangeSet 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
29Comparing hearing ranges Which animals hear the lowest and the highest frequencies?100,00010,0001,000100101frequency(Hz)Frequency low (Hz) high (Hz)HumanDogBatElephantMouseCatDolphinhumandogbatelephantmousedolphin
30Hearing 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.
31Measuring loudness – the decibel scale 16014012010080604020personal stereopermanent ear damageaircraftoverheadloud bellcircular sawat 2mquietcountrysidepin beingdroppedcan just be heard
323. putting noisy machinery in insulated rooms Noise and its effectsA 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. headaches2. nausea3. deafnessList three ways of reducing the effects of loud noise.1. ear protectors2. double glazing3. putting noisy machinery in insulated rooms
338L Sound and Hearing What is sound? Speed of sound Reflecting sound Contents8L Sound and HearingWhat is sound?Speed of soundReflecting soundThe ear and hearingSummary activities
34amplitude – The height of a wave, which shows how loud Glossaryamplitude – The height of a wave, which shows how louda 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, whichshows 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 isdetected by the ears.