How do we measure energy?

We measure energy by the amount of work it does. We measure it in foot-pounds. For example, 20 foot-pounds is the amount of energy it would take to lift 2 pounds 10 feet, or 10 pounds 2 feet, or 5 pounds 4 feet. We also measure energy in cal¬ories. A "small calorie," the kind people count when they are dieting, is a thousand times bigger — so a man on a strict diet might eat only enough food to give him 3,000,000 foot-pounds of energy a day. We also measure energy in joules, ergs, horsepower-hours, kilowatt-hours, and all sorts of units, depending on the kind of work we mean.