Mass, volume and a balance
Does air, a gas, have mass? Yes. A football that is flat and the same football pumped hard, weighed on a kitchen scale by a grown-up, show it: the pumped ball has a little more mass, because the extra air squeezed inside is matter. Other tests give properties of solids. Place objects in a bowl of water: some float and some sink. A magnet pulls on only a few metals: iron, nickel and steel. Aluminium foil and copper are not magnetic, even though they are metals (but many coins are made of steel inside, so test yours), and plastic and wood are not magnetic at all. Each test gives one property, so we use several to describe an object.
| Object | In water | Magnet |
|---|---|---|
| steel paperclip | sinks | pulled |
| cork | floats | not pulled |
| copper coin | sinks | not pulled |
| plastic bottle cap | floats | not pulled |
Sink, float and magnet (a grown-up helps). Collect six small objects, such as a cork, a coin, a paperclip, a pencil, a small stone and a foil ball. Predict, then test each in a bowl of water and with a magnet. Record in a table. Which results surprised you?
| Ball | Mass |
|---|---|
| flat | 430 g |
| pumped up | 436 g |