Physics of a Commode

Introduction

The commode you use every day is a fairly complex hydrodynamic device.  This animation will discuss how it works.

Physics

            The main task of the commode is to use the water in the tank to start and sustain a siphon that removes the waste from the bowl.  That task requires some fairly complex timing to avoid using more tank water than necessary. 

 

Siphon

            A siphon is a tube filled with water that has, in steady state, its lowest exhaust water level lower than its intake water level.  Dynamically, the siphon can use fluid inertia to flush most of the water out of the tube even when the above conditions are not met.  That is the case for the final phases of the commode flush.