State which of the following are open systems with respect to energy, and which are closed: a car, a person, an insulated picnic chest, the Universe, the Earth. Explain why.

Energy is defined as the “ability or capacity to do work, which is the ability to exert a force causing displacement of an object.”

It can be in the form of potential energy, kinetic energy, thermal energy, electrical energy, chemical energy, nuclear energy, or any other form.

The major difference between a closed and an open system (in terms of energy) is that in a closed system, the total energy cannot change (there is no inflow or outflow of energy), whereas it can in an open system.

$$\begin{gathered} {\mathrm{\Delta E}}_{\mathrm{open}\mathrm{system}}\ne 0 \\ {\mathrm{\Delta E}}_{\mathrm{closedsystem}}=0 \end{gathered}$$

• Open systems: An automobile, a person, and the Earth are all open systems. Through its exhaust, a car exchanges energy with its environment (among others). A human exchanges energy with the environment by eating and heat (for example, to maintain a consistent body temperature). Because the Earth gets heat from the Sun and then radiates it into space, its overall energy fluctuates.
• Closed systems:An insulated picnic trunk and the Universe are both closed systems. Because no heat can be transported from or to the picnic chest if it is completely insulated, it is a closed system. Nothing can change the overall energy of the Universe because there are no systems outside of it.

Therefore, an automobile, a person, and the Earth are all open systems in terms of energy. An insulated picnic chest and the Universe are both closed systems in terms of energy.