Water hammer

Water hammer is a nickname for the effects of the kinetic energy of a body of water in motion. Moving water in a pipe has kinetic energy proportional to the velocity of the water times the mass of the water in a given volume. If the pipe is suddenly closed, the mass of water behind the closure is still moving forward with some force. In domestic plumbing this is experienced as a loud bang resembling a hammering noise. Air traps are sometimes added to water systems to provide a cushion to absorb the force of moving water in order to prevent damage to the system. The water hammer principle can be used to create a simple water pump.