Two Ways To Move Energy
- First way: the object itself travels, like a thrown stone or a bullet
- Second way: a wave carries the energy across, and nothing else moves
- A stone in a pond makes the water molecules vibrate up and down
- The ripple crosses to the bank and splashes. The energy has arrived
Presenter notes: Open with a question and refuse to answer it yet. Say: I am standing here and my voice is reaching the back of the room. Something must be travelling from my mouth to your ears. What is it? Somebody will say air. Push back gently: if air were travelling from my mouth to the back wall, this room would have a permanent wind in it, and it does not. So something goes from here to there, but it is not the air, and it is not any object at all. Tell them that today they will find out exactly what it is, and that the answer also explains ripples in a pond, why sunlight reaches us across empty space, and why a drum sounds louder when you hit it harder.