Energy & Your Body

Food, power and efficiency

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• 1 kcal ≈ 4184 J; a day’s food (≈ 2500 kcal) averages about 120 W.
• Muscles are about 25% efficient; the rest becomes heat.
• Climbing hundreds of metres burns only a modest snack.

Steps

1. Calories are energy
2. A human light bulb
3. Running upstairs
4. Why exercise makes you hot
5. Burning a chocolate bar
6. Burning off a chocolate bar