The Toilet: a Marble of Physics

Cristina Monroig

Most human beings see a toilet as their personal device to dispose of waste, but the truth is that it is much more than that, it is a complete marble of physics. Toilets are one of the best examples of the power of the siphon effect. This is the key element for the physical formulation of the product, for instance, allows it to get rid of so much water and waste rapidly.
 

In order to get the job done efficiently, this appliance uses components such as the bowl, the toilet tank, the flushing valve, and the refill mechanism. The bowl’s unique design is what truly allows it to evacuate a large amount of water and therefore waste. Hence, without the bowl and its exclusive design this astonishing contribution to modern hygiene would not be present.
 

As mentioned before, the key is the siphon effect. With this object, the siphon is a pipe with an S-shaped vent which is molded into the bowl. It is what is responsible for keeping the volume of water in the bowl constant. Also, it acts as a seal preventing unpleasant gases and smells from coming up through the sewer pipe. If water is added to the bowl, little by little, the toilet won’t flush. Hence, when the toilet is being used the water rises slightly and overflows into the siphon pipe, still not enough to initiate the siphon effect. For that one needs a lot of water all at once to push the water in the siphon over the vent. For instance, dumping a big bucket of water into the bowl would get the job done by filling the siphon and triggering a flush.
 

In this case, the toilet tank acts as a bucket of water. When the handle is pressed, the chain lifts the flush valve uncovering the drain hole allowing water to rush out and fill the bowl in a matter of about six seconds. The fluid enters the bowl through the holes in the rim and through the hole called siphon jet, which pushes most of the tank water straight in to the siphon’s tube. The hurry of all this water is what triggers the siphon, allowing the water and waste to go down the drain. Once this crucial step of filling up the siphon pipe is done, gravity does the rest thanks to the cohesive forces in liquids. These forces get water molecules to pull on their neighbors when falling from the siphon high point. It is important to clarify that gravity is the one that creates the siphon and not a change in pressure. When the water in the bowl is almost all drained, air enters the siphon pipe, stops the flush and produces that other familiar sound of gurgling. Finally, once the water in the tank empties, the flush valve, which has been floating since the toilet was flushed, falls back into place.