Temperature Layers

Are your feelings for science a bit hot and cold? Yes? Then we have the perfect activity for you!

Australian Curriculum links

  • Science > Physical Sciences > Year 3 > ACSSU049
  • Science > Chemical Sciences > Year 5 > ACSSU077

You'll need

  • Large clear jar
  • Smaller jar
  • 2 small glass bottles that can lay on their sides on the base of the smaller jar if the smaller jar is turned upside down
  • Red and blue food colouring
  • Icy water
  • Hot water
  • Tap water

Try this

  1. Fill the large jar with tap water.
  2. Lower the smaller jar into the water and allow it to fill with water. Turn the smaller jar upside-down and stand it in the bottom of the large jar to create a platform.
  3. Add blue food colouring to one of the small bottles and fill the bottle with icy water.
  4. Add red food colouring to the other small bottle and fill it with hot water.
  5. Cover the top of one bottle with your thumb and lower it into the large jar, carefully placing it on its side on the platform.
  6. Repeat step 5 with the other bottle.
  7. Watch carefully to see what happens to the icy, blue water and the hot, red water. (The icy, blue water should sink to the bottom and the hot, red water should rise to the top.)

Further investigation

Make a salt solution in one of the small bottles by mixing salt with tap water until salt can no longer be dissolved in the water. Add a few drops of red food colouring to the salty water. Place the bottle on its side on top of the platform. Watch the water to determine which direction the red water will travel.

What's happening?

This activity is all to do with density. Density is a measure of how tightly matter is packed together—it’s the mass per unit of volume of a substance. If we’re talking about the density of water, what we mean is how many water molecules (teeny, tiny little pieces of water) there are in a given volume.

The density of water changes with temperature. Temperature is a measure of energy, so hot water has more energy than cold water. The hot water in this activity has lots of energy. The hot water molecules move around a lot, spreading out so the hot water becomes less dense than the rest of the water molecules in the large jar. Because the hot water is less dense, the hot water molecules rise, taking red food colouring with them.

It’s the opposite for the cold, blue water. The cold water molecules aren’t moving around much and therefore occupy less space. The cold water has a higher density than the rest of the water in the large jar, so the cold water molecules sink, taking blue food colouring with them.

Real world links

At normal atmospheric pressure, water reaches its highest density at a temperature of 4°C. At temperatures above 4°C, water molecules have more energy and spread out. Below 4°C water molecules have less energy and don’t move around as much. As the temperature drops below 4°C, water forms an ice-like structure and ice crystals start forming in the liquid. At 0°C water freezes into ice. This makes ice less dense than liquid water. Water is the only substance that has a lower density as a solid than as a liquid.