Sound

Touch your throat and talk. You’ll feel vibrations. Turn your speakers up and put your hand on them, you’ll feel vibrations. These vibrations produce sound waves, which travel through the air.  

A vibration through a medium produces a sound wave.

All speakers have something that moves backwards and forwards, creating vibrations. This movement moves the air molecules backwards and forwards creating a sound wave.

No one can hear you scream in space

For sound to work, it needs a medium like a solid, liquid or gas. In space where there are no air molecules to vibrate, no sound happens.

We know that the physical properties of solids, liquids and gases are different, and as such, the movement of sound through each state of matter is different.

It might surprise your to learn that sound actually travels faster through denser objects.

Sound travels at:

• 340 m/s in air
• 1500 m/s in liquids
• 5000 m/s in steel

If we look at the structure of a solid compared to a liquid we can see why sound travels faster in a liquids compared to gasses.

Since the particles in a solid are closer together the vibrations can travel quicker from particle to particle, meaning the message (sound) travels faster.

The video to the right demonstrates the speed at which sound and light travel. Each student is observing the explosion in a different manner. One will see it (light), another will hear it (sound) and the last one will feel the sound vibrations through the ground (sound).

Unlike sound light is much faster. Travelling at 300,000,000 m/s. This is why we can see a lightning bolt before hearing it.

It can also travel through a vacuum, which is the reason why we can still get the suns rays through space.

Going at or faster than the speed of sound means you break the Speed barrier. Felix Baumgartner jumped from 24 miles above the earths surface, becoming the first person to travel at the speed of sound.

Questions

Don’t forget to write down the questions you got wrong in full!

Short answer Questions

1. Explain how sound is created

2. Why can sound move faster through metal than air?

3. Copy and Complete the sentence below:

Sound is produced by objects that are _______ . This makes the air molecules _____ and produces a sound wave. Sound travels fastest in _______ and slowest in ______, and cannot travel through a ______.

4. When predators approach a heard of elephants, the elephants will stomp their feet to notify others. Why don’t they simple blow their trunks instead?

5. Research and explain how snakes ‘hear’ predators coming?

6. If you were a predator in the jungle, would it be more beneficial to have well developed eyes or well developed ears? Explain your answer (4 marks)

Extension Questions

7. Why doesn’t sound travel in a vacuum?

8. What factors does the speed of sound depend upon? What are some factors that it does not depend upon?

9. Why would it be futile to attempt to detect sounds from other planets, even given the very best in audio detectors?

10. A cat can hear sound frequencies up to 70,000 Hz. Bats send and receive ultra high frequency squeaks up to 120,000 Hz. Which hears sound of shorter wavelengths, cats or bats?

11. Explain how sound proof windows work?