Water under pressure in pipes is subject to the force of gravity in the same manner as a body falling through the air. To illustrate: When water flowing through a pipe is suddenly checked, a noise is heard, caused by the striking of the water against the end of the pipe or whatever stops the flow. The noise is heard at every part of the pipe and in case of a long length of pipe the noise appears to repeat itself very quickly. This "chattering" is called water hammer. Water faucets that shut off the water quickly always have water hammer. Its effect is often sufficient to break a pipe. Faucets that gradually check the flow of water overcome water hammer. An air cushion at the end of pipe will often overcome this noise.