Waves - Sound

Waves: Sound KS4 Physics

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

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

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

How does sound travel? 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? How does sound reach your ear? longitudinal wave

The bell-jar experiment Remove the air from the bell jar and what happens to the sound? There is air inside the bell jar so the sound can travel and be heard. With a vacuum inside the bell jar, the sound cannot be heard. Why? Place a ringing clock inside the bell jar and what happens? vacuum pump on

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

How fast does sound travel? How are these values used to estimate the speed of sound?  Record the results of your sound experiments in a table. 100 0.34 294 4 3 2 1 speed (m/s) time (s) distance (m) sound = 294 m/s distance time speed = = 100 0.34

How fast does sound travel?

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? 340 m/s Do you think the speed of sound in water is the same as it is in air? The speed of sound in air is about…

Different speeds of sound

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

Sound and states of matter 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. Sound waves travel fastest through solids . Sound waves travel by particles vibrating. What state does sound travel fastest through and why? solid gas liquid

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

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

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

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

Experiment on echoes 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? START 150 m STOP Stand at least 100 m from a large, flat wall with a stop watch.

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

Echoes and reflection What do we call reflected sound? an echo Are hard or soft surfaces best at reflecting sound? 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 Hard surfaces produce strong echoes.

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

Studying sound waves loudspeaker signal generator oscilloscope

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 oscilloscope loudspeaker Sound waves can be studied with this type of equipment.

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

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

Why sound is low pitch or high pitch? 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? low pitch sound high pitch sound What is the difference between the sound wave of a low pitch sound and a high pitch sound?

Which is the highest? 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 . Which trace represents the sound with the highest pitch? B A

Wave animation

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

How does the ear hear?

Can we hear all frequencies? Set the volume and increase the frequency of the signal provided by the signal generator. 20 Hz to 20 000 Hz Humans cannot hear sounds of every frequency. What is the hearing range of a healthy young person? The range of frequencies you can hear is called your hearing range .

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

Comparing hearing ranges 100 000 10 000 1 000 100 10 1 0 human dog elephant bat mouse dolphin Do all animals have the same hearing range? frequency (Hz)

How is loudness measured? 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 1000 times 1000 times How much more powerful than the quietest sound is 30 dB ? A whisper is 30 dB and normal conversation is 60 dB . How much more powerful is normal conversation compared to a whisper? The loudness of a sound is measured in decibels ( dB ).

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. 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. What might also influence hearing loss? Why are there laws about the maximum levels of sound that people should be exposed to at work?

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. nausea headaches deafness List three ways of reducing the effects of loud noise. ear protectors putting noisy machinery in insulated rooms double glazing

How loud is loud? 160 140 120 100 80 60 40 20 0 permanent ear damage decibels can just be heard aircraft overhead circular saw at 2m quiet countryside pin being dropped loud bell personal stereo

How is hearing tested? It records the softest sound heard at each pitch . The audiogram shows hearing sensitivity for different frequencies ( pitch ) at different intensities ( volume ). 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

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

What is ultrasound? Any high frequency sound above 20 kHz is called… Whales and dolphins communicate using ultrasound. Why does a dog whistle vibrate at ultrasound frequencies? Can you name another human use of ultrasound? ultrasound The upper frequency limit of human hearing 20 000 Hz.

Using ultrasound dolphins ultrasonic toothbrush jewellery cleaning imaging fetuses submarines viewing kidney stones echo location bats ultrasonic cleaning It’s a trick question! All of the above involve ultrasound. High frequencies can be very useful! Which of the following does not use ultrasound?

Using ultrasound in medicine 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? fetus at 10 weeks fetus at 20 weeks 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.

How does ultrasound imaging work? 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. Ultrasound, like all sound, is reflected when it meets different boundaries. So how is this used for imaging?

Sound multiple choice