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1 of 40 © Boardworks Ltd 2008 2 of 40 © Boardworks Ltd 2008 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. 3 of 40 © Boardworks Ltd 2008 Module 2.2 Topic 1: 13/05/2017 Waves Objectives: Describe waves and Understand the movement of waves. • BELL TASK: Draw a star diagram (mind map) with the word WAVE at the centre and suggest 4 other EXAMPLES of WAVE with the names and pictures. e.g. Mexican Wave e.g. Wave for surfing 4 of 40 © Boardworks Ltd 2008 Describing Wave 2•nd Write Task of the lesson and Complete the sentences: down the- Copy keywords that we can use to describe waves: 1. Waves happen when something is •Crisp pushed and then pulled, or back and then •Vibrate forwards. •Back-and-forth •Powerful 2.•Up-and-down 1 part vibrates in a wave, other parts •Saying-goodbye vibrateEnergy one after the other as well. •Transfer •Block Energy 3.•Push-and-Pull Waves start from a one place and go •Crests-and-Troughs outwards. 5 of 40 © Boardworks Ltd 2008 Simulation of a transverse wave 6 of 40 © Boardworks Ltd 2008 What do transverse waves look like? •A Slinky can be used to model transverse waves, by moving one end of the Slinky up and down. •coils vibrate •up and down •source moves •up and down •direction of wave •The wave travels away from the source. The direction of the wave is at right angles to the movement of the source. •In a transverse wave, the coils do not travel horizontally, each coil of the Slinky just vibrates up and down. 7 of 40 © Boardworks Ltd 2008 •peak •trough •The high points of a transverse wave are called peaks and the low points of a transverse wave are called troughs. •amplitude •wavelength •wavelength •amplitude •wavelength •Thewavelength amplitude ofofany orbetween the lowest •The anywave waveisisthe thehighest distance two points from the rest point. matching points on neighbouring waves. 8 of 40 © Boardworks Ltd 2008 3rd Task of the lesson – Match the keywords Waves 1. The high points of a transverse wave Crests 2. The low points of a transverse wave Troughs 3. Between the crests to the mid-point, or between the troughs to the mid-points Amplitude 4. Distance between two matching points Wavelength Distance between the crests to the troughs is……………… Twice the Amplitude 9 of 40 © Boardworks Ltd 2008 Label the picture with the keywords Crest Trough 10 of 40 Amplitude Wavelength © Boardworks Ltd 2008 4th Task of the lesson – Watch the simulations and answer the questions: 1. What happened when a pulse of wave is sent to a fixed end? It gets reflected back on the opposite side. 2. What happened when a pulse of wave is sent to a loose end? It gets reflected back on the same side. 3. GOLD Challenge! What is different when we send a many waves to a loose and then a fixed end? The waves get reflected stronger! 11 of 40 © Boardworks Ltd 2008 Summary: show Mr. Tsui your answers for VIVO’s! • Describe transvers waves. • What happens to transvers waves when they hit an end? 12 of 40 © Boardworks Ltd 2008 Wavelength of a transverse wave •The wavelength of any wave is the distance between two matching points on neighbouring waves. •wavelength •wavelength •wavelength •The wavelength is the same whichever two matching points are used to measure this distance. •The symbol used to represent wavelength is . 13 of 40 © Boardworks Ltd 2008 Amplitude of a transverse wave •The amplitude of any wave is the maximum distance a point moves from its rest position. •amplitude •amplitude •The amplitude of a transverse wave is the height of a peak or trough from the wave’s rest position of the wave. •The larger the amplitude, greater the energy of the wave. 14 of 40 © Boardworks Ltd 2008 How do Sound Wave Travel? Saturday, 13 May 2017 BRONZE: Describe longitudinal waves? SILVER: Explain how sound wave changes? MONDAY = KEYWORD DAY BELL TASK:Match and copy the meanings of the NEW keywords 15 of 40 © Boardworks Ltd 2008 Watch the Video and Match the Boxes Good vibrations! What vibrates so that each of these objects makes sound? drum skin harp strings 17 of 40 mouth blowing horn lute strings © Boardworks Ltd 2008 How does sound travel through the air? 18 of 40 © Boardworks Ltd 2008 Copy and complete • Something vibrates • Object’s vibration pushes air particles along • Air particles push each other along and make a longitudinal wave 19 of 40 © Boardworks Ltd 2008 ‘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. 20 of 40 © Boardworks Ltd 2008 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. 21 of 40 © Boardworks Ltd 2008 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. 22 of 40 © Boardworks Ltd 2008 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 23 of 40 B Sound B has the greater number of waves across the oscilloscope – it has the highest frequency and so has the highest pitch. © Boardworks Ltd 2008 Amplitude and wavelength 24 of 40 © Boardworks Ltd 2008 Describing sound waves 25 of 40 © Boardworks Ltd 2008 Sound waves summary 26 of 40 © Boardworks Ltd 2008 27 of 40 © Boardworks Ltd 2008 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 1. When you see the cymbals crash, press start. 2. When you hear the cymbals crash, press stop. 28 of 40 © Boardworks Ltd 2008 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? distance speed = = time 29 of 40 100 = 294 m/s 0.34 © Boardworks Ltd 2008 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. 1. How does this calculation for the average speed of sound compare with the real speed? 2. What errors could have affected the results of the cymbals experiment? 3. Do you think the speed of sound in water is the same as the speed of sound in air? 30 of 40 © Boardworks Ltd 2008 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 31 of 40 kinetic energy of air particles kinetic energy in eardrum © Boardworks Ltd 2008 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. 32 of 40 © Boardworks Ltd 2008 Sound waves in different materials 33 of 40 © Boardworks Ltd 2008 Speed of sound in different materials 34 of 40 © Boardworks Ltd 2008 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 10,000 0.35 28,571.4 meteorite The jet fighter and the meteorite travel faster than the speed of sound in air. This is called breaking the sound barrier. 35 of 40 © Boardworks Ltd 2008 36 of 40 © Boardworks Ltd 2008 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. 37 of 40 © Boardworks Ltd 2008 Investigating echoes Plan an investigation to measure the speed of sound using echoes. You may use any of the following equipment: stopwatch clapper board starting pistol hard, flat surface Remember to make sure it is a fair test. 38 of 40 © Boardworks Ltd 2008 Analysing your results Calculate the speed of sound for each of your distances using the formula below. distance speed = time 1. How do your calculations compare with the actual speed of sound in air? 2. Which of your distances gave the most accurate answer? 3. Were there any errors in your experiment? 4. Could you improve the experiment in any way to make it even more accurate? 39 of 40 © Boardworks Ltd 2008 40 of 40 © Boardworks Ltd 2008 How do we hear? 41 of 40 © Boardworks Ltd 2008 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. 2. The waves travel along the ear canal. 3. The waves reach the eardrum and make it vibrate. 42 of 40 5. The cochlea 4. The small bones turns these (ossicles) amplify into electrical the vibrations. signals. © Boardworks Ltd 2008 The ear and hearing summary 43 of 40 © Boardworks Ltd 2008 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 44 of 40 © Boardworks Ltd 2008 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. 45 of 40 © Boardworks Ltd 2008 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? 46 of 40 © Boardworks Ltd 2008 Should ‘Mosquitoes’ be banned? 47 of 40 © Boardworks Ltd 2008 Animals’ hearing ranges 48 of 40 © Boardworks Ltd 2008 Ordering volumes 49 of 40 © Boardworks Ltd 2008 Reducing noise 50 of 40 © Boardworks Ltd 2008 51 of 40 © Boardworks Ltd 2008 Glossary 52 of 40 © Boardworks Ltd 2008 Anagrams 53 of 40 © Boardworks Ltd 2008 Multiple-choice quiz 54 of 40 © Boardworks Ltd 2008