Not Heavy or Light. Denser or Less Dense
- A one gram needle sinks. A ship of thousands of tonnes floats
- So heaviness cannot possibly be the rule
- Denser than the liquid: it sinks. Less dense: it floats
- It is a comparison between two things, never a fact about one
Presenter notes: Bring a bowl of water, a sewing needle and a large block of wood. Ask which will float. Everybody says the wood, because the needle is only a gram and the block is far heavier. Drop them both in. The needle goes straight to the bottom and the heavy block sits on the surface. Then ask the question that lasts the whole period: if a one gram needle sinks and a wooden block a hundred times heavier floats, then heaviness is clearly not the rule. So what is? Tell them the answer is a comparison, not a measurement, and that the same idea explains why a steel ship stays up.