How can you make your own thermometer?

Materials:

Per group of pupils:

• A rigid plastic bottle with a lid
• Play dough or moDELLing clay, e.g. Plasticine
• A transparent plastic drinking straw
• A pair of scissors
• Food coloring (optional)
• Tap water

Procedure:

1. Use a pair of scissors to make a hole in the top of the bottle lid, big enough for the drinking straw to fit through.
2. Fill the bottle halfway with cold water.
3. Add a few drops of food colouring and mix.
4. Screw on the bottle lid and insert the straw through it into the water, making sure that the straw does not touch the base of the bottle.
5. Seal around the hole in the lid using play dough, thereby fixing the straw in place. The seal must be completely airtight.