5.2 Hearing
Unit 2, Theme 1 – My Family
Learning objectives
• How do sound waves travel
• What is the range of human hearing (in
hertz)?
• What is the impact of loud sounds on the
environment, society and our health?
• Explain how longitudinal waves travel from
vibrating objects to our ears for us to hear
sounds.
• Know that the human hearing range is
• 20–20 000 Hz
How do you hear a drum playing ?
• Sound travels as a wave from the drum to
your ear
• Drum hit
• Vibrates
• Makes air molecules vibrate
• passes energy onto next particles
Transverse waves
•
•
•
•
Light waves
Other electromagnetic waves
Water waves
Seismic waves
vibration
• Compression – particles are squashed
together
• Rarefaction – particles are spread out
Longitudinal waves
• Sound waves
• Waves in a stretched spring
Transverse and Longitudinal waves
• http://www.bbc.co.uk/schools/gcsebitesize/sc
ience/edexcel_pre_2011/waves/anintroductio
ntowavesrev2.shtml
• http://www.acs.psu.edu/drussell/demos/wav
es/wavemotion.html
• http://www.physicsclassroom.com/mmedia/w
aves/lw.cfm
• http://www.acoustics.salford.ac.uk/feschools/
waves/wavetypes2.php
sound
• Vibrating objects cause sound waves
• Can only travel when there are particles to
vibrate
• Sound passes through solids quickly
• Gases more slowly
• Not at all in space
• Why?
Measuring sound
•
•
•
•
•
•
How quickly it vibrates
Frequency in hertz
One cycle per second = 1 hertz
We can’t hear less than 20 hertz
Frequency is too low for us to hear
Highest pitched – 20000 hertz – or 20
kilohertz
• Sounds above that are called ultrasound
Age and sound
• Older you get the less you can hear high
frequency sounds
Noise levels
• Measured in decibels
• As the reading goes up by ten the sound gets
ten times louder
Rock concert - 120 decibels
Dicso – 100 decibels
decibels
• The concert is 100 times louder than the disco
•
•
•
•
120-100 = 20
Two lots of 10 means
10 times
And ten times again
Damage your hearing at 85 decibels
Damage depends on
• The loudness of the sounds
• How long you are listening
• How often your hear them
activity
Sound level
decibels
Maximum time
to avoid hearing
damage
whispering
20
No harm
Power drill
95
4 hours
Jet engine
140
No safe limit
Rock concert
120
1 minute
MP3 player
120
1 minute
MP3 player
•
•
•
•
•
•
Can damage your hearing
Bus. Train, car
Listen for a long time
Can start to suffer from tinnitus
Look this up
Use ear phones that fit inside the ears – blocks
out background noise more effectively
The law
• Employers must not expose employees to
sound above 87 decibels on a daily basis
• Not at all to sounds over 140 decibels
protection
Noisy neighbours
• Parties
• Barking dogs
• Can sort it between
neighbours
• Can go to the
council
• Can go to court and
be ordered to stop
the noise
Did you know?
• ‘Mosquitoes’ have been installed in shopping
centres
• Speakers that play very high pitched noises
• Who can hear these noises?
• What are they trying to do?
• What frequency should it be set at?
Did you know?
• Astronauts in space communicate by radio as
sound waves cannot travel in a vacuum.
• Victims of earthquakes attract attention more
effectively by tapping on pipes rather than
shouting
Key points
• Sound travels as longitudinal waves through
gases, liquids and solids
• Humans can hear sounds between 20 hertz
and 20000 hertz
• Very loud sounds can damage hearing or
disturb other people.