The Physics Behind the Flushing Toilet

 

The flushing toilet system is quite a simple system when it comes to physics. As was talked of before, the tank on the back of most toilets is filled with water. This stored water has a potential energy of

PE = mgh

where m=mass of the water, g=the accelleeration due to gravity, and h=the water's height above ground.

Once this water is released it is converted from potential energy to kinetic energy.

As well, when the water is rushing into the bowl it has a total momentum of all of the combined momentums that separately rush into the bowl. The basic equation for this is

P=mv

where P = momentum, m = mass, and v = velocity

This momentum of the rushing water creates enough momentum in the still water of the bowl to begin its movement through the p-trap.

Picture Borrowed From: www.toiletology.com/history.htm

Once the water has enough energy to move over the last curve of the p-trap it is pulled down (or drains down) the rest of the drain by the pull of gravity (once again PE converted to KE). Once it is flowing fast enough trough the last pipe it begins a pulling motion on the rest of the water still in the bowl, due to its larger potential energy past the p-trap.

Picture borrowed from: www.physics.purdue.edu/ demo/2C/siphon.html

This is known as a siphon which, due to the tensile strength of water, creates its own vacuum by pulling itself through the p-trap, sucking everything left in the bowl out through the p-trap and away.