Mechanical waves transfer energy through matter called the medium . Water waves carry energy through water. Sound waves carry energy through gasses, like air, and through some liquids and solids. Radio waves, X rays, and light waves, do not need matter to transfer energy. In a transverse wave , particles of matter vibrate up and down at right angles to the direction in which the wave travels.
Sound waves are compression waves that move back and forth parallel to the direction of the wave.
A compression is the part of the wave that is pushed together. The of a compression wave where particles of matter are spread apart is called a rarefaction . The crest of the wave is the top of a transverse wave or the point of greatest compression in a compression wave . A trough is the bottom of a transverse wave or the point of greatest rarefaction. The node is a halfway point between a crest and trough.