Sound

Our ears magnify sound 20 times

Resonance is what makes opera singers break glass when they hit a high note. The frequency of the voice matches the vibrations of glass molecules making it break.

Folds in the wall absorb sound (making it quiet outside) and prevent echoes

How Are Sounds Made?

• Sounds are made when objects vibratevibrate (shake from side to side)

• Loudspeakers can create large vibrations

• Guitar strings vibrate

• Drum skins vibrate

• Air vibrates inside a recorder

• Our vocal cords vibrate when we speak

How Does Sound Travel?

• Sound needs atoms to travel throughatoms to travel through

• It can travel through solids, liquids and gases like air

• It cannot travel through a vacuumcannot travel through a vacuum

• You would not be able to make noise in space!

The Speed of Sound

• The speed of sound through the air is 330 m/s• It is 1,480 m/s through water• It is 5,100 m/s through Steel• Through which state of matter does sound travel

quickest?• Solids• Why?• The atoms are closer together, so they are

more able to pass on vibrations

Thunderstorms

• The speed of light is 300,000,000 m/sec• Sound travels at 330 m/sec• Why do you see lightning before you hear

thunder?• Light from the lightning is 1 million times

quicker than sound• If you count from when you see a lightning flash

to when you hear a clap of thunder and this takes 3 seconds. How far away is the storm?

• 3 x 330 = 990 metres

How do bats travel?

• Bats cannot see very well, but they are superb night fliers.

• They use echolocation to find food (moths)

• They make a high pitched squeak that bounces off objects

• These echoes tell bats whether they are about to fly into a tree or catch their dinner

Loudness• Loudness is also called Amplitude• It is measured in Decibels (dB)• Rock bands uses Amplifiers to make their

music louder• Big vibrations cause loud sound e.g. thumping a

Lambeg drum

Amplitude on an Oscilloscope

An oscilloscope shows the shape of vibrations

Sound travels as waves

A quiet sound is like a very small wave

A loud sound has a large wave

Both the quiet and loud sounds are the same width

Trivia• The whispering gallery in St. Paul’s Cathedral can carry whispers 30m • The Doppler Effect is when sounds coming towards us get higher in

pitch, but as they move away they get lower• The Eustachian tube allows air from the nose to equalise pressure on

the ear drum

Pitch

• Pitch is also called frequency • It is measured in Hertz (Hz)• Frequency is how fast something is

vibrating• We cannot hear some high pitched

sounds, like dog whistles• A deep voice (baritone) has a low pitch• http://www.bbc.co.uk/wiltshire/content/articles/2006/04/04/

mosquito_sound_wave_feature.shtml • http://www.jetcityorange.com/MosquitoRingtone.html

Frequency on the Oscilloscope

• High pitched (frequency) waves are close together• Dolphin (http://www.geocities.com/CapeCanaveral/1046/audio1.html)

• Low pitched (frequency) waves are spread apart• Both waves are equally loud (because they are the same

height)

Our Ear

The Ear

Our Ear

• Our audible range is between 20 – 20,000 Hz when we are young

• As we get older this gets smaller• Loud sounds like aeroplanes taking off,

jackhammers, mp3 players and rock concerts can burst our ear drums

• Our ear drums can heal • If the cochlea is damaged our hearing is

permanently damaged and we may need a hearing aid

The Audible Range of Different Animals

All the animals, except for the elephants can hear higher pitched sounds than us

Loudness of Sound

• Sound at 140dB can burst you ear drums• Mp3 players can go up to 100dB• Workmen using road drills wear ear protection

Ultrasound

Ultrasound scans are used on pregnant women to check on their baby

High pitched sounds are sent into the womb and reflect back from the foetus

Sonar scanning is used by trawlers to detect if there is shoals of fish beneath them

Submarines use sonar to detect wear the sea bed is

Wavelength and Frequency

• High pitched sounds have a high frequency and a short wavelength

• http://www.acoustics.salford.ac.uk/schools/index1.htm