Why is a perpetual motion machine impossible?
• The phrase “perpetual motion” is old-fashioned language. It does not mean simply something that stays in motion forever. This might be theoretically possible—it at least does not violate conservation of energy. But the phrase “perpetual motion” uses “motion” in an older sense to mean motor or engine, and it means something that can deliver energy—to run an automobile, for example—without requiring any external source of energy, such as gasoline. It means something for nothing.
