What is Energy?

• A. The rate of doing work.
• B. The capacity of a physical system to do work.
• C. The degrees of temperature.
• D. The force applied to a unit area.

Answer: (B)

Energy is the capacity to do work. It’s what a system has that lets it cause changes, move objects, or change its state, in whatever form that energy takes (kinetic, potential, chemical, thermal, etc.). It’s not the act of doing work itself—that’s work—and the rate at which work is done is called power. The other options mix up ideas: temperature measures how hot or cold something is, not energy; force applied to a unit area is pressure, not energy; and the rate of doing work describes power, not energy. Think of energy as the stored ability to perform work—like a battery’s stored chemical energy, a moving object’s kinetic energy, or a stretched spring’s elastic potential energy.