cavitation

A phenomenon that occurs when fast objects travel through fluids, creating an area of high pressure in the front and leaving behind it an area of low pressure, akin to the slip stream formed by a truck moving on a highway that will suck you forward behind it, i.e. the reason why bikers draft behind each other and migratory birds fly in a V formation, in order to save energy. As the static pressure of a liquid is decreased to below the liquid's vapour pressure, it will change phase and vapourize, turning into a gas, thus forming small vapour-filled cavities or bubbles in the liquid that eventually collapse super violently and with high speed, creating a shockwave. Cavitation is the main reason for damage to boat propellers, as the phenomenon causes tons of little indentations to the blades. Mantis shrimps (fig.) use cavitation to crack open the shell of mollusks on which they feed. These marine crustaceans have a raptorial appendage which they strike with the velocity of a bullet, thus generating a cavitation bubble that collapses with so much power that it sometimes releases a flash of light in a process called sonoluminescence, and creating a shockwave of energy so strong that it can crack open shells and clams, and potentially break aquarium glass. Cavitation is also used by the Thresher Shark, a certain type of shark that flings its long whip-like tail over its head with speeds of up to 50 kilometers an hour at the peak of the tail, in order to create a shockwave that either stuns or kills its prey. 回