Sound

Chapter 48

Sound is a form of Energy

Sound is caused by

something been made to

vibrate.

Sound is a form of Energy

• These vibrations then travel through a medium, such as air.

• When they reach the eardrum they cause it to vibrate and our brain detects the sound.

Sound needs a medium inwhich to travel.

• Sound needs a medium in which to travel. It cannot travel through a vacuum.

• As the air is removed from the Bell jar the sound from the bell gets weaker and weaker until it cannot be heard anymore.

Sound needs a medium

Echoes

• An Echo is a reflection of sound.

• Bats use echoes to determine their position

Experiment to show the reflection of sound

• Set up apparatus as shown.

Result

• The metal sheet reflects the sound.

• The angles i and r are equal.

Reflection of Sound

Ultrasound

• Bats make use of this to avoid obstacles. They emit ultrasound(a note of high frequency that humans cannot hear) and can determine distance by the time it takes for the sound to return.

• Ultrasound is also used in medicine to see inside the body and to shatter gallstones and kidney stones.

Sonar

• Ultrasound echoes are used by ships to determine the depth of sea below them.

Speed of Sound

• In air, sound travels at a speed of 340m/s.

• It travels faster in liquids and fastest of all through solids.

• Light travels much faster than sound.

• An example of this is thunder and Lightning.

Hearing protection

Measuring the loudness of sound.

• The decibel is the unit used to compare the loudness of sounds.

• Regular exposure to noise above 85 decibels could be harmful if ear protection is not worn.

160

140

120

100

80

60

40

20

0

decibels

circular saw at 2m

quiet countryside

pin being dropped

can just be heard

loud bell

personal stereoaircraft overhead

Measuring loudness – the decibel scale