All waves do the same thing, transfer energy from one place to another, but there are two types of waves, mechanical and electromagnetic. All waves that need a medium to move through are called mechanical waves. These include sound waves, ocean waves and seismic wave. In mechanical waves, the medium may move but will return to its original position. Waves that need a medium to travel through cannot through travel a vacuum such as space, because they have nothing to move through. These waves work by moving energy from particle to particle, until they reach their destination. Electromagnetic waves, however, such as light, x-rays, and radio waves, do not need a medium to travel through, and can travel through empty space. That is why the sun's rays are able to travel to earth. Although these 2 types of waves are different, they can be measured in many of the same ways. The first type is a transverse wave, which are waves that carry energy by moving at right angles to the direction of the energy flow. Ocean waves, and most electromagnetic waves are have a transverse wave pattern. The highest point of a transverse wave is the crest, while the lowest point is called the trough. The distance between the middle of the wave and the crest is called the amplitude, which is used to measure how much energy the wave has, the larger the amplitude, the more energy the wave is carrying. To find a wave's wavelength, you either measure the distance between two adjacent crests, or to adjacent troughs. Another way of measuring transverse waves is by their frequency, which is the number of waves that pass a certain point in one second, and is usually measured in hertz. The other type of measuring waves is compressional waves, which move my displacing matter back and forth in the direction of the energy flow. Sound travels in this type of wave, by preforming a series of compressions that travel through the air.