“The system” is a large ship and everything inside it. The ship turns off its engines, and is floating in the ocean. No material enters or leaves the ship during the process. Some descriptions of this situation are given below. For each, indicate whether it is true or false, and explain why.

A. The system is not at equilibrium, because equilibrium implies no external forces are acting on the system and the ship has forces acting upon it. The system is at a steady state, however, because the forces acting upon it are balanced.

B. The system is not at equilibrium, because the force of gravity is acting upon the ship but there is no upward force balancing the downward force of gravity. However, the system is at a steady state, because it is not moving.

C. The system is both at equilibrium and at a steady state, because the ship is not moving, and there is no driving force for motion: the forces acting upon it balance each other and there is no driving force for change.

D. The system is neither at equilibrium nor at a steady state, because no object in the ocean is perfectly motionless. The ship bobs up and down with the waves, and likely drifts in a horizontal direction due to currents. If the position of the system is changing, it can’t be at steady state or equilibrium.