A P-wave or pressure wave is a wave in which the wave motion or vibration occurs longitudinally (in the direction of wave motion) rather than laterally (at right angles to wave motion) as in S-waves or shear waves. The wave energy reverberates horizontally forward and back in a "spring-like" manner. Sound waves and compressional seismic waves are examples of P-waves. P-wave energy can be transmitted through a fluid (gas or liquid) whereas S-wave energy dissipates in a fluid. Thus sound waves propagate through air and seismic P-waves pass with refraction through the Earth's molten core. S-waves do not pass through the Earth's core leaving a seismic shadow on the side opposite the epicenter.
