The steady state bottle kit can be used to model how the temperature of a steady state system is determined by the flow of energy in and the flow of energy out of the system. Water is used to represent energy and the level of water in the bottle represents temperature. The bottle can be set up so that water can be run into it from a tap, while at the same time water can flow out of it into a sink. Eventually the water reaches a steady level at which the input balances the output. This set-up is a model, for example, of a centrally heated house or of the climate system of the Earth, and can be used to explore the effects of changing the rate of inflow or outflow, and negative and positive feedback.

The steady state bottle kit contains the parts required to make the system (plastic drinks bottle and clip not included).