1 of 40© Boardworks Ltd 2008. 2 of 40 3 of 40© Boardworks Ltd 2008 What causes sound? The tuning...

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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?

Sound travels because the vibrating object makes nearby particles vibrate.

Sound needs a medium to travel through – it cannot pass through a vacuum.


• 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.

Module 2.2 Topic 1: 21/04/23

WavesWavesObjectives: Describe waves Describe waves and and Understand the movement of wavesUnderstand the movement of waves..

WAVE

e.g. Wave for surfing

e.g. Mexican Wave


Describing Wave

• Write down the keywords that we can use to describe waves:

•Crisp•Vibrate•Back-and-forth•Powerful•Up-and-down•Saying-goodbye•Transfer Energy•Block Energy•Push-and-Pull•Crests-and-Troughs


Simulation of a transverse wave


•A Slinky can be used to model transverse waves, by moving one end of the Slinky up and down.

What do transverse waves look like?

•The wave travels away from the source. The direction of the wave is at right angles to the movement of the source.

•source moves•up and down

•direction of wave

•coils vibrate•up and down

•In a transverse wave, the coils do not travel horizontally, each coil of the Slinky just vibrates up and down.


•trough

•peak

•The high points of a transverse wave are called peaks and the low points of a transverse wave are called troughs.

•wavelength

•wavelength

•wavelength

•amplitude

•amplitude •The amplitude of any wave is the highest or the lowest points from the rest point.

•The wavelength of any wave is the distance between two matching points on neighbouring waves.


Crests

Troughs

Amplitude

Wavelength

Twice the Amplitude


Label the picture with the keywords

Crest

Trough

Amplitude

Wavelength


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!

http://phet.colorado.edu/sims/html/wave-on-a-string/latest/wave-on-a-string_en.html


Summary: show Mr. Tsui your answers for VIVO’s!• Describe transvers waves.

• What happens to transvers waves when they hit an end?


•The wavelength of any wave is the distance between two matching points on neighbouring waves.

Wavelength of a transverse wave

•The wavelength is the same whichever two matching points are used to measure this distance.

•wavelength

•wavelength

•wavelength

•The symbol used to represent wavelength is .


•The amplitude of any wave is the maximum distance a point moves from its rest position.

Amplitude of a transverse wave

•The amplitude of a transverse wave is the height of a peak or trough from the wave’s rest position of the wave.

•amplitude

•amplitude

•The larger the amplitude, greater the energy of the wave.


MONDAY = KEYWORD DAYBELL TASK:Match and copy the meanings of the NEW keywords

BRONZE: Describe longitudinal waves?SILVER: Explain how sound wave changes?

How do Sound Wave Travel?Friday 21 April 2023

Watch the Video and Match the Boxes


Good vibrations!

What vibrates so that each of these objects makes sound?

harp stringslute strings

drum skin

mouth blowing horn


How does sound travel through the air?


Copy and complete

• Something vibrates

• Object’s vibration pushes air particles along

• Air particles push each other along and make a longitudinal wave


If we connect an mp3 player to a speaker, we can all hear the sound produced.

‘Seeing’ sound waves

If we also connect an oscilloscope to the mp3 player then we can ‘see’ the sound waves.

speaker oscilloscope


A sound can be quiet or loud.

Loudness and amplitude

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.

quiet sound loud sound


A sound can be high or low – this is the pitch of the sound.

Pitch and frequency

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:

low pitch high pitch

The greater the frequency of the waves on the trace, the lower/higher the pitch.


Which trace represents the loudest sound?

Which wave is the loudest and highest?

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?

Sound B has the greater number of waves across the oscilloscope – it has the highest frequency and so has the highest pitch.

A B

A B


Amplitude and wavelength


Describing sound waves


Sound waves summary



This investigation for calculating the speed of sound should be carried out in a quiet open space.

Speed of sound – experiment

1. When you see the cymbals crash, press start.

2. When you hear the cymbals crash, press stop.

100 m

One student should hold a stopwatch, whilst another should be holding some cymbals 100 metres away.


Experiment

Record the results of the sound experiment in a table like this:

Speed of sound – results

100 0.34 2941

2

3

4

Distance (m) Time (s) Speed (m/s)

How are these values used to estimate the speed of sound?

=100

0.34294 m/s=speed =

distance

time


The first cymbal experiment gives an estimate for the speed of sound as 294 m/s.

Speed of sound – analysis

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?


Energy transfer

How many different energy transfers do you think take place during this experiment?

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

When the cymbals crash there is a transfer of kinetic energy from the cymbals to the air particles.


Sound needs a substance through which to travel because it travels by making particles vibrate.

Sound in different materials

Which state of matter does sound travel fastest through?

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.

Sound waves travel fastest through solids.


Sound waves in different materials


Speed of sound in different materials


Which of these travel faster than the speed of sound in air?

Breaking the sound barrier

The jet fighter and the meteorite travel faster than the speed of sound in air.

This is called breaking the sound barrier.

120600small aeroplane

jet fighter

cheetah

meteorite

Distance (m)

5

Time (s) Speed (m/s)

900

50

10,000

2

2.5

0.35

450

20

28,571.4



What happens when a sound wave meets a hard flat surface?

Reflected sound

The sound wave is reflected back from the surface.

This is called an echo.


Plan an investigation to measure the speed of sound using echoes.

Investigating echoes

Remember to make sure it is a fair test.

You may use any of the following equipment:

stopwatch

hard, flat surfacestarting pistol

clapper board


Calculate the speed of sound for each of your distances using the formula below.

speed =distance

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?

Analysing your results



How do we hear?


How does the ear work?

6.The auditory nerve takes the signals

to the brain.

1. Sound waves are collected by the outer ear (or pinna).

3. The waves reach the eardrum and make it vibrate.

4. The small bones (ossicles) amplify the vibrations.

5. The cochlea turns these into electrical signals.

2. The waves travel along the ear canal.


The ear and hearing summary


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 range of frequencies can you hear?

What is the hearing range of a healthy young person?

Humans can only hear sounds of certain frequencies. The range of frequencies a person can hear is called their hearing range.

20 Hz to 20,000 Hz


Does everyone have the same hearing range?

Hearing ranges and hearing loss

We all have slightly different hearing ranges.

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.


Hearing ranges

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.

As we get older, our ability to hear high pitched sounds deteriorates. Some shopkeepers use this to their advantage.

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?


Should ‘Mosquitoes’ be banned?


Animals’ hearing ranges


Ordering volumes


Reducing noise



Glossary


Anagrams


Multiple-choice quiz

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