The common method of digital recording on a magnetic material. The bits are laid out end to end, and the direction of the magnetic charge is horizontal with respect to the medium. THIS DEFINITION ...
compressions are regions of high pressure due to particles being close together rarefactions are regions of low pressure due to particles being spread further apart ...
ripples on the surface of water vibrations in a guitar string a Mexican wave in a sports stadium electromagnetic waves - eg light waves, microwaves, radio waves seismic S-waves ...