Materials:

• An empty medicine bottle or other small bottle
• A cork to seal the bottle
• A nail
• A glass tube from an eye-dropper
• Water
• Food colouring
• A felt pen

   1) Make a hole in the cork with the nail. Push the glass tube into the hole. Fill the bottle right to the top and add a few drops of food colouring. Carefully seal the bottle with the cork. When the cork is in place, the coloured water should rise about halfway up the glass tube. There you go. You’ve just made a thermometer.

   2) With the felt pen, mark the level of the water and the current temperature. Now put your thermometer in places where you know the temperature won’t be the same (for example, on a sunny windowsill, or in the fridge, or in a pot of hot or cold water). At each spot, note the level of the water in the glass tube.

Note: You have to leave the thermometer in place for at least an hour. This gives the water time to react to the temperature in its new environment.

What’s happening?

Water goes up in the tube when the temperature is hotter, and goes down when it’s colder. Why? Because liquids expand when they’re heated and contract when they’re cooled. As the water in your homemade thermometer absorbs heat, it expands and climbs higher in the tube. When the water comes in contact with cold, it contracts and slides lower down in the tube. Commercial thermometers use alcohol or mercury because they react to changes in temperature very quickly.

Materials:

• A balloon
• An empty pop bottle
• A pot of hot water

   Stretch the balloon and place it over the mouth of the bottle.

   Put some water in a pot and boil it. Turn off the heat and stand the bottle up in the pot of hot water. Wait 5 minutes.

WHAT’S GOING ON?

The air inside the bottle expands as it heats up. The molecules start to move faster and faster,and to move farther apart – and that causes the balloon to inflate.