Sound

Junior Science: Physics

Revised Science Syllabus Extract

Main Topic Sub-topics

3B5 Sound

 

• transmission of sound• speed of sound• vibrations and sound

3B6 Reflection of sound

Hearing

• reflection of sound• echoes• sound detection in the ear• sound levels • hearing protection

Learning Outcomes for 3B5 and 3B6

On completion of this section, students should be able to

OP40 show that sound is a form of energy, and understand that sound is produced by vibrations

OP41 show that sound transmission requires a medium and echoes are reflected sound

Learning Outcomes for 3B5 and 3B6

On completion of this section, students should be able to:

OP42 understand that the ear detects sound vibrations and that exposure to very loud sounds can cause damage to the hearing

OP43 recall that the speed of sound is less than the speed of light

OP44 explain the time lag between seeing and hearing the same event

Equipment and Resources

• Shatter resistant rulers

• Bell jar, sound source – alarm clock, vacuum pump

Can you guess what these sounds are?

Beluga Whale Shrimp

Sound

SOUND

• Sound energy can be converted into other energy forms

What is sound?

• Sound is a form of energy

Sound energy

Sound energy Kinetic Energy

Sound energy (contd.)

Sound energy can be converted into other energy forms

Sound energy Electrical energy

How is sound created?

Sound is created when objects vibrate

Vibrations

• Sound is produced by vibrations of the air molecules

• A sound wave is just a moving pattern of changes in air pressure

What is a sound wave?

Sound wave

CompressionRarefactionPressure

Time

Vibrating ruler

Transmission of sound

• Sound requires a medium in order to be transmitted

• Sound can be transmitted through a solid, liquid or gas

• Sound cannot travel in a vacuum

Non-mandatory experiment to showSound needs a medium in which to

travel

What are echoes?

• Sound can be reflected off surfaces

• Echoes are sounds that are reflected from a surface

• Sound reflection can be used to calculate distance

How do bats use sound?

Echolocation

What is the speed of sound?

• Speed of sound differs in different materials

• Speed of sound in air at average temperatures and average pressure is approximately 340m/s

Speed of sound (contd.)

• Sound does not travel through all materials at the same speed

• Sound travels through water at approximately 1500m/s

• Sound travels through iron at approximately 6000m/s

The speed of sound and the speed of light

• Speed of sound is much smaller than the speed of light

• Speed of sound

350m/s

• Speed of light

300 000 000m/s • Calculate the distance by counting the seconds

Seeing an event before we hear it

• Fireworks

• Waves crashing on a beach

in the distance

How do humans create sound?

• Sound is produced by air rushing from your lungs past your vibrating vocal chords

• These vibrations caused fluctuations in the rushing air, which formed a sound wave

How do we hear sound?

• The vibrations travel through the air to our ears

• Our eardrums vibrate with the sound

• The vibrations are passed on through the ear, changed to electrical energy and transmitted to the brain

• The brain then interprets and gives the sound meaning

Sound

Can you guess what these sounds are?

Humpback whaleFrog

Hearing DamageHow much sound causes permanent damage?

0

20

40

60

80

100

120

140

1 minute

Below this level (70dB) – hearing damage negligible

15 minutes

dB

Sound Level is measured in Decibels

Source of sound or noise Sound level

(in decibels)

Jet taking off at distance of 30m 140

Threshold of pain 120

Disco loudspeaker 3m away 120

Pneumatic drill at road works 10m away

100

Busy street traffic 70

Ordinary conversation 60

Average whisper 20

Threshold of hearing 0

Noise Protection

• Mandatory ear protection

• Ear muffs or ear plugs

• Required in certain work

environments where sound >

70dB

Assessment of student understanding

• Combination of homework and a class quiz Homework• An automatic focus camera is able to focus on

objects by use of an ultrasonic sound wave. The camera sends out sound waves which reflect off distant objects and return to the camera. A sensor detects the time it takes for the waves to return and then determines the distance an object is from the camera. If a sound wave (speed = 340 m/s) returns to the camera 0.150 seconds after leaving the camera, how far away is the object?

Class Quiz - Sound1. What is sound?

2. Give an example of sound energy being converted into another energy form?

3. How is sound produced?

4. What does sound need in order to be transmitted?

5. Why is there no sound in a vacuum?

6. What is an echo?

7. What is name used for the technique whereby some animals use sound for location?

8. What is the approximate speed of sound in air?

Class Quiz – Sound (contd.)

9. The speed of sound in air can change with changes in __________ and ___________ ?

10. Through which of the following materials would sound travel faster (a) air, (b) water (c) iron

11. Why does sound travel faster in iron than in air?12. During a storm a person hears the thunder before

seeing the lightening, Why?13. Why do people who work in noisy environments

wear ear protection?

BIBLIOGRAPHY

• Websites

• http://www.acoustics.salford.ac.uk/schools/lesson4/flash/waves1.swf

• http://www.colorado.edu/physics/phet/web-pages/simulations-base.html

• http://www.coolnotions.com/AGifs/AGifs.htm

• http://www.findsounds.com/ISAPI/search.dll

• http://www.gifanimations.com/action/ImageDisplay?group=2&category=155&index=29&dir=stay

• http://www.harrythecat.com/graphics/b.html

• Http://www.juniorscience.ie• http://www.oceanlink.island.net/oinfo/acoustics/

AcousticAccomplish.html#Anchor-The-49575 • http://www.partnersinrhyme.com/soundfx/carsoundfx.shtml

• http://www.physics.brown.edu/physics/demopages/Demo/waves/demo/3b3030.htm

• http://science.howstuffworks.com/hearing1.htm• http://www.sounddogs.com/searchresults.asp• Textbook – Exploring Science , 2003

O’Callaghan, M., Reilly, S. and Seery A., The Educational Company

BIBLIOGRAPHY (contd.)