Mechanical Waves and Longitudinal Waves
There are two types of mechanical waves. The first is longitudinal. The second is transverse. All mechinical wave must go through a medium, such as water, air, and a solid (earth)
A longitunal wave is the displacement of the medium is parallel to the propagation of the wave. A good example is a slinky. When you pull on a slinky, then release, you can see a wave move down the slinky to the other end. That is a wave. The wave you can see moving down the slinky is called compression. The other part is rarefaction. http://hyperphysics.phy-astr.gsu.edu/hbase/sound/tralon.html
A longitunal wave is the displacement of the medium is parallel to the propagation of the wave. A good example is a slinky. When you pull on a slinky, then release, you can see a wave move down the slinky to the other end. That is a wave. The wave you can see moving down the slinky is called compression. The other part is rarefaction. http://hyperphysics.phy-astr.gsu.edu/hbase/sound/tralon.html
Transverse Waves
A transverse wave is the displacement of the medium is perpendicular to the direction of propagation of the wave. Moving a string is an good example. Say if you tied a string on a pole, and you held the other end. If you moved the string up and down, it'll look like waves like in the photo. The top of the wave is the crest; that is the highest point. The bottom is the trough; that is the lowest point. From one wave to the other, that is the wavelength. From the crest to the trough, that is the amplitude. http://hyperphysics.phy-astr.gsu.edu/hbase/sound/tralon.html
Mechanical Wave and Earthquakes
An earthquake has both transverse and longitudinal waves. In earthquakes a P wave is a longitudinal wave. The P waves travels through the deeper earth. An S wave is the transverse wave. This wave travels the surface, causing buildings to knock over.