Sound needs air to move through, if theres no air theres no sound how does this work?? does anyone know?

Question

I just see this experiment on TV it was on a kids show and they didn't explain why and how it works.

They set an alarm off and put it under a glass jar, you coud still hear it but when she sucked the air out with a pump the sound faded untill you couldn't hear it and then she pumped he air back in and you could hear it again.

How does this work im confused as the alarm bell was still going but you couldn't actually hear it.

Answer 1

Because sound is a mechanical wave and longitudinal in nature.

Since these waves are the result of mechanical disturbance in medium therefore it can travel in only mechanical media(e.g. metals,air,liquids).

Answer 2

every thing travels within air, if theirs no air you can't hear anything

Answer 3

iam from egypt we can to be good and hot friendly?

Answer 4

Sounds is the movement of air particles created by a vibrating source.   If there is no air, the air cannot move and create sound (the vibrating source can vibrate but there is nothing to transfer the vibrations to)

http://www.neurophys.wisc.edu/~ychen/tex...

In space, no one can hear you scream....

Answer 5

The bell creates noise through motion. This motion is transferred to the surrounding medium (in your example, the air) by displacing it. When there is no surrounding medium, there is nothing to transfer the motion to, hence no sound.

The human ear can hear things that vibrate between 20 and 20000 times per second. Other animals have slightly different ranges (think dog whistle).

The way your ear works is to sense small vibrations in the air (via very small hairs). These small vibrations are converted to sound in your mind (more specifically, they're converted to electrical nerve impulses along your auditory nerve and these are then converted to sound in your brain).

Note that this is true for any fluid (water, oil, methane, etc). The only difference is that sound travels at different speeds through these media. Consider dolphins and whales - their ears are tuned to the frequencies at which vibrations are propagated though water.