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KS4 Physics Waves: Sound.

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Presentation on theme: "KS4 Physics Waves: Sound."— Presentation transcript:

1 KS4 Physics Waves: Sound

2 Waves: Sound What is sound? Sound and reflection
Contents Waves: Sound What is sound? Sound and reflection Structure of sound waves Hearing sound Ultrasound

3 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.

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

5 How does sound travel? How does sound reach your ear?
longitudinal wave When the drum skin is struck, it vibrates which causes the air beside the drum to vibrate. The compression and stretching of air particles creates a sound wave which is carried through the air to your ear. What type of wave is a sound wave?

6 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? With a vacuum inside the bell jar, the sound cannot be heard. Why?

7 How fast does sound travel?
You need a quiet open space at least 100 m long to perform this investigation. START STOP 100 m 1. When you see the cymbals crash, press START. 2. When you hear the cymbals crash, press STOP.

8 How fast does sound travel?
 Record the results of your sound experiments in a table. sound 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

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

10 Different speeds of sound

11 Sound and states of matter
Sound waves need a substance to travel through. What are all substances made of? particles solid liquid gas What is the particle model of a solid, a liquid and a gas? In which state are the particles closest together? solid In which state are the particles furthest apart? gas

12 Sound and states of matter
Sound waves travel by particles vibrating. What state does sound travel fastest through and why? 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 waves travels faster.

13 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. 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?

14 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 break the sound barrier. What does this mean?

15 Waves: Sound What is sound? Sound and reflection
Contents Waves: Sound What is sound? Sound and reflection Structure of sound waves Hearing sound Ultrasound

16 Reflected sound waves What happens when a sound wave meets a
hard flat surface? The sound wave is reflected back from the surface. What type of sound does this produce? echo

17 Experiment on echoes 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. How far does the sound travel?

18 Experiment on echoes 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 speed?

19 Echoes and reflection What do we call reflected sound? an echo
Are hard or soft surfaces best at reflecting sound? Hard surfaces produce strong echoes. How are echoes reduced in cinemas and theatres? By using soft materials on the walls such as curtains. Name two animals that use echoes for navigation or communication. bats and dolphins

20 Waves: Sound What is sound? Sound and reflection
Contents Waves: Sound What is sound? Sound and reflection Structure of sound waves Hearing sound Ultrasound

21 Studying sound waves Sound waves can be studied with this type of equipment. loudspeaker oscilloscope signal generator Which piece of equipment… produces signals over a range of frequencies and of varying amplitudes? converts signals into sound waves? is used to study the frequency and loudness of a sound? signal generator loudspeaker oscilloscope

22 Why sound is quiet or loud?
What is the difference between the sound wave of a quiet sound and a loud sound? quiet sound loud sound The loud sound has taller waves. The louder the sound, the greater the amplitude. What would the sound wave of a very loud sound look like?

23 Which is the loudest? A B Which trace represents the loudest sound?
Sound A is the loudest. Sound A has the largest amplitude, which means the wave has more energy and so the sound is louder.

24 Why sound is low pitch or high pitch?
What is the difference between the sound wave of a low pitch sound and a high pitch sound? low pitch sound high pitch sound The high pitch sound has a shorter wavelength, so more waves are visible. It has higher frequency waves. What would the sound wave of a very low sound look like?

25 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 shortest wavelength and the most number of waves visible, so it has the highest frequency.

26 Wave animation

27 Waves: Sound What is sound? Sound and reflection
Contents Waves: Sound What is sound? Sound and reflection Structure of sound waves Hearing sound Ultrasound

28 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.

29 How does the ear hear?

30 Can we hear all frequencies?
Set the volume and increase the frequency of the signal provided by the signal generator. Humans cannot hear sounds of every frequency. The range of frequencies you can hear is called your hearing range. What is the hearing range of a healthy young person? 20 Hz to Hz

31 Do we have the same hearing?
Does everyone have the same hearing range? We all have slightly different hearing ranges but 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. People lose the ability to hear sounds of high frequency as they get older. Which end of their hearing range will be affected?

32 Comparing hearing ranges
Do all animals have the same hearing range? 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

33 How is loudness measured?
The loudness of a sound is measured in decibels (dB). 0 dB = quietest audible sound (near total silence) 10 dB = 10 times more powerful than the quietest sound 20 dB = 100 times more powerful than the quietest sound How much more powerful than the quietest sound is 30 dB? 1000 times A whisper is 30 dB and normal conversation is 60 dB. How much more powerful is normal conversation compared to a whisper? 1000 times

34 When is sound dangerous?
Any sound above 85 dB can damage hearing. You know you are listening to 85 dB sound if you have to raise your voice to be heard. What might also influence hearing loss? The amount of time spent listening to a loud sound also causes hearing problems. Any 140 dB sound causes pain and immediate damage! More than two hours of 100 dB sound can damage your ears. Why are there laws about the maximum levels of sound that people should be exposed to at work?

35 What is noise? A noise is any unwanted sound.
What one person considers noise another person might not. Can you name any examples? List three effects of noise. headaches nausea deafness List three ways of reducing the effects of loud noise. ear protectors double glazing putting noisy machinery in insulated rooms

36 How loud is loud? 160 140 120 100 80 60 40 20 decibels personal stereo
personal stereo permanent ear damage aircraft overhead loud bell circular saw at 2m quiet countryside pin being dropped can just be heard

37 How is hearing tested? The results of a hearing tested are shown on an audiogram. frequency of sound (Hz) intensity of sound (dB) loud sound moderate sound soft sound low pitch high pitch The audiogram shows hearing sensitivity for different frequencies (pitch) at different intensities (volume). It records the softest sound heard at each pitch .

38 Testing hearing Which audiogram trace represents optimal hearing and which represents impaired hearing? frequency of sound (Hz) intensity of sound (dB) impaired hearing optimal hearing

39 Waves: Sound What is sound? Sound and reflection
Contents Waves: Sound What is sound? Sound and reflection Structure of sound waves Hearing sound Ultrasound

40 What is ultrasound? ultrasound
The upper frequency limit of human hearing Hz. Any high frequency sound above 20 kHz is called… ultrasound Whales and dolphins communicate using ultrasound. Why does a dog whistle vibrate at ultrasound frequencies? Can you name another human use of ultrasound?

41 ultrasonic toothbrush
Using ultrasound Which of the following does not use ultrasound? imaging fetuses dolphins jewellery cleaning ultrasonic toothbrush viewing kidney stones bats ultrasonic cleaning echo location Use the internet or research books to find out about other uses of ultrasound. These keywords should help. submarines It’s a trick question! All of the above involve ultrasound. High frequencies can be very useful!

42 Using ultrasound in medicine
Ultrasound is the name given to a medical technique. It uses high frequency sound waves to produce images of inside the body without opening up the body. fetus at 10 weeks fetus at 20 weeks X rays are more energetic and penetrating and are a lot more dangerous, they could cause damage to the growing baby. Why is ultrasound for scanning fetuses instead of X rays which would give a clearer picture?

43 How does ultrasound imaging work?
Ultrasound, like all sound, is reflected when it meets different boundaries. So how is this used for imaging? An ultrasound machine transmits high-frequency sound waves into the body. These sound waves are reflected different amounts by different tissues. The reflected waves are detected by a receiver. A computer turns the distance and intensities of these echoes into a two-dimensional image.

44 Sound multiple choice


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