Expansion of liquids and gases

Liquids and gases expand when heated too.

Activity 9.4 — a liquid expanding

Fill a test tube with coloured water and close it with a stopper carrying a glass tube. Mark the water level in the tube (A), then stand the test tube in hot water.

Figure to be added

Figure 9.22 — (a) coloured water at level A; (b) in hot water the level first drops to B, then rises to C.

The observation

The level first drops a little to B, because the glass warms and expands first. Then the water warms and expands more than the glass, and the level rises to C. Mercury and alcohol thermometers use exactly this.

Activity 9.5 — a gas expanding

Stand an empty, open bottle in ice and water for a while, then fit a balloon over its neck and move the bottle into hot water.

Figure to be added

Figure 9.23 — a bottle with a balloon on its neck: (a) in ice, the balloon limp; (b) in hot water, the balloon inflated.

The observation

The cold air in the bottle warms above room temperature and expands; it cannot escape past the balloon, so the balloon inflates. Taken out again, the air cools and contracts and the balloon shrinks. Air expands when heated and contracts when cooled.