Link-up Summary: Sound

Sound is a form of energy caused by vibrations. 

Click on the picture to see the animation.

Sound is produced when particles vibrate.
A loudspeaker creates sound because is causes the air around it to vibrate in a pattern of waves that reaches your ear... see the animated version here.

The sound of your voice is produced when your vocal chords vibrate as air is passed over them.

Hearing 

The ear is a sense organ which detects sound vibrations. Exposure to very loud sounds can cause damage to your hearing.

• The outer ear collects the sound and channels it along the ear canal. 
• The middle ear (ear drum and tiny bones called hammer, anvil and stirrup) conducts the sound into the inner ear. 
• The inner ear converts the sound energy (vibrations) into an electrical signal which can be sent to the brain. 
• The auditory nerve is a sensory nerve which sends electrical signal to the brain. 

This animation shows the structures in the ear very clearly. 

Sound needs a medium to travel through

Because sound is transmitted through the vibration of particles, sound needs a medium to travel through, such as air or water.

A vacuum is a space that is completely empty of matter. There are no particles in a vacuum. Sound cannot travel through a vacuum.

This animation shows a bell inside a jar. When all the air is drawn out of the jar, and a vacuum is created, you can no longer hear the sound of the bell.

Because sound cannot travel through a vacuum, this means that sound cannot travel in outer space.

This article talks about sound at high frequencies... and how students can hear sounds that teachers probably cannot hear! 

Speed of sound 

Sound travels more quickly through materials that are more dense.

Check it out: tap your finger lightly on the desk. You probably hear a quiet sound. Now lay your ear on the desk and tap again. Can you hear a difference?



Sound can travel through the solid material of your desk more quickly than through the air.

Sound travels faster through liquids than it does through gases, such as air. So the speed of sound in water is 1500 metres per second, while the speed of sound in air is only 340 metres per second.

Thunder and lightning 

Thunder and lightning originate at the same moment. However you can often see the lightning before you hear the thunder. This is because light travels faster than sound. Learn how to calculate how far away you are from the storm here.

Echoes 

Echoes are reflected sound.

Ships use echolocation to measure the depth of the sea below them.

Fishing boats can also use echolocation to detect shoals of fish swimming beneath the boat.

Click on the picture to see the animation

And finally...

How do we know that sound is a form of energy?

Remember that sound is a form of energy, caused by vibrations. Here is a video of an Irish physics teacher demonstrating that sound is a form of energy. Energy is the ability to do work or to move something. The sound energy from the speaker causes the flame of the candle to move.

Knowledge check:

OP40   Show that sound is a form of energy, and explain that sound is produced by vibrations

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

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

Post compiled by Ms McCarthy. The website thephysicsteacher.ie contains many helpful links which I have used in this blogpost.