v. perked, perkÂ·ing, perks. v.intr. 1. To stick up or jut out: dogs' ears that perk. 2. To carry oneself in a lively and jaunty manner.
However instead of crests and troughs, longitudinal waves have compressions and rarefactions. Definition 1: Compression. A compression is a region in a longitudinal wave where the particles are closest together. A rarefaction is a region in a longitudinal wave where the particles are furthest apart. As seen in Figure 1, there are regions where the medium is compressed and other regions where the medium is spread out in a longitudinal wave. The region where the medium is compressed is known as a compression and the region where the medium is spread out is known as a rarefaction.
The propagation of an acoustic wave through a solid polymer can be characterised by two parameters: sound velocity and sound absorption. Sound speed, u (in m/s) is the rate at which sound waves travel through the medium. Sound absorption or attenuation Î± (in dB/m) is a measure of the loss of energy of the sound wave as it travels through the medium: the energy of the sound wave is converted into thermal motions or heat, but usually with a negligible rise of temperature only.