1 of 40© Boardworks Ltd 2008 What causes sound? The tuning fork vibrates and you hear a sound....

1 of 40 © Boardworks Ltd 2008

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.


How does sound travel through the air?


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


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


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.


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.


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 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.


Animals’ hearing ranges


Ordering volumes


Reducing noise


Glossary


Anagrams


Multiple-choice quiz

1 of 40© Boardworks Ltd 2008 What causes sound? The tuning fork vibrates and you hear a sound....

Documents

Transcript of 1 of 40© Boardworks Ltd 2008 What causes sound? The tuning fork vibrates and you hear a sound....