Who Is Actually Doing Work?
- The guard standing at the gate: force, but nothing moves. No work
- The girl reading: her mind is busy, but nothing is being pushed anywhere
- The man playing the madal: hands strike and move. Work is done
- The man walking: he pushes the ground and moves. Work against friction
Presenter notes: Ask a strong student to come out and push the classroom wall as hard as they can for thirty seconds while everybody watches. Let them go red in the face. Then ask the class how much work was done. Everyone says a lot, and he certainly agrees. Tell them the answer is zero, exactly zero, and let the protest happen because the protest is the lesson. Do not explain yet. Say only that physics uses the word work to mean something very precise, that by the end of the period they will understand why the answer is zero and will be able to defend it, and that they will also be able to catch out any adult who says holding a heavy load is hard work.