What you need:
- A glass bottle
- A straw
- Modelling clay
- Water
- Food colour
- A container
- A glove
What to do:
1. Add a few drops of food colouring into the empty bottle.
2. Pour cold tap water over it, filling the bottle right up to its neck.
3. Now, place a straw into the bottle. Holding most of its length out of the bottle (the other end should be in the coloured water though), pack the modelling clay around the straw, sealing the bottle’s mouth.
4. Fill the container with hot water. Place the glass bottle into the container. What happens?
5. Wear the glove and transfer the bottle to a container containing cold water.
What happens:
When the bottle is placed in hot water, the water level in the straw goes up. When the bottle is in cold water, the water level in the straw goes down again. This indicates that the level of water reflects the change in temperature, just like a thermometer.
Why?
When water heats up, it expands. That means that its molecules spread out and the space between them increases. Because the bottle is sealed and the straw is the only opening, the water expands and moves into the straw. The more it is heated, the more water expands and the level in the straw rises. Similarly, when the water cools down, it contracts causing its molecules to draw closer together. This causes the water level in the straw to fall.
If you draw a makeshift scale on the straw using a marker (refer a normal thermometer for how the scale should look), you can actually monitor the temperature change with respect to the expansion and contraction of water.
Picture Credit : Google
