Energy used in play
Choose a game or exercise, your body mass and how long you play, and work out how much food energy your body uses, in kilocalories and in rotis.
Core concept
Energy used (kcal) ≈ MET × body mass (kg) × time (hours), where the MET says how many times harder than resting an activity is; harder play, a heavier body and longer play all use more energy
Topic: Our body and health
Our muscles burn food to move, and the harder they work, the faster they use energy: What is needed to make things move, heat up, light up or grow. All key words. Scientists compare activities with a number called the MET: sitting still is 1 MET, walking about 3.5, cycling 6, football 7, running 9.8 and skipping with a rope about 11. To a good guess, the energy used in kilocalories is the MET × your body mass in kg × the time in hours. So the energy depends on three things: how hard the activity is, how heavy the body is, and how long you keep going. A roti gives about 100 kcal, so we can see how much food a game uses up.
What you will learn
- Work out the energy used in an activity from its MET, body mass and time.
- Compare activities by how fast they use energy.
- Relate the energy used to the energy in food.
Before you start
- Know that food gives energy, measured in kilocalories (kcal).
Materials
- A stopwatch or watch
Equipment
- A bathroom scale
Procedure
- Record an hour of football for a 35 kg student.
- Change the activity to running and record.
- Change the mass to 45 kg and record.
- Change to 30 minutes of walking and record.
How this simulation is simplified
- MET values: walking 3.5, cycling 6, football 7, running 9.8 (about 9 km/h), skipping 11.
- kcal = MET × mass (kg) × hours is an adult rule of thumb; it is only a rough guide for children.
- One roti gives about 100 kcal.