Clock

Many engines operate by undergoing engine cycles. An engine cycle is a sequence of steps, also called strokes. The cycle returns the engine to its original configuration; for example, the engine has the same temperature at the beginning and end of a cycle. During a stroke, the engine may exchange heat with a hot or cold reservoir. Also, a property of the engine might change during a stroke—for example, the engine’s pressure or volume (if the engine is classical) or trap strength (if the engine is an ion). A clock appears near the top of the sculpture, illustrating the importance of ordering and timing the strokes properly.