Sound Waves : Gate Academy

Sound waves come from a vibrating source, e.g. loudspeaker.
As the loudspeaker cone vibrates, it moves forwards and backwards, which squashes and stretches the air in front of it.
As a result, a series of compression (squashes) and rarefactions (stretches) travel out through the air, these are sound waves.

Sound waves are longitudinal; they have compressions and rarefactions and oscillate backwards and forwards.
Humans can hear frequencies between 20 and 20000 Hz.
Sound waves need a medium to travel through.
Ultrasound Waves are high frequency sound waves, medically used to look at structures and organs inside the human body, i.e., to form an image of a fetus in a womb.
Compression is the high pressure section of the wave
Rarefaction is the low pressure section of the wave
The higher the frequency, the higher the pitch
The higher the amplitude, the louder the sound

When sound reflects off a wall, it will come back to you; an echo.
If you know the distance between you and the wall, and you can measure how long it takes for the echo to sound, you can figure out the speed of sound in air.
Remember to take into account that the sound has gone there and back.