Pressure waves

Pressure wave in a tube

A pressure wave is a (usually longitudinal) wave that is caused by changes in pressure that moves particles around. Sound is a good example of a pressure wave because it makes pressure differences that move around that is clearly seen when glass vibrates and breaks in front of a very loud sound because of the pressure waves. A shockwave is also a mix of pressure waves bunching up on a supersonic object making a very loud sound called a sonic boom. A whip is a very easy tool to demonstrate a sonic boom. The velocity of a very fast object is measured in Mach number, a unit based on the speed of sound in air, about 343 meters per second. There is not a "universal" speed of sound because the speed of sound depends on the medium it travels through. In the picture, notice the red part that is an increase of pressure where there are a lot of molecules. changes in pressure can also cause wind so a pressure wave can also cause wind like sound blowing out a candle.