Can I show how differences in density can cause water to move ?

You can demonstrate this by completing this experiment.

What will I need to do this?

1 adult
1 empty plastic soda bottle, 1 liter size
scissors
4 ice cubes
spoon
blue food coloring
measuring cup (250 ml)

How do I do this ?

Ask an adult to cut a plastic soda bottle in half.
In the bottom half of the cola bottle pour cold water from the faucet and place 4 ice cubes in the water. Stir the water with a spoon to cool it, then remove the ice.
Pour warm water from the faucet in the measuring cup. Place enough blue food coloring to produce a dark blue liquid in the measuring cup.
Turn the top side of the soda bottle upside down like a funnel and place it the bottom section of the bottle.
Tilt the measuring cup so that half of the warm, blue water slowly runs into the soda bottle funnel.
Notice the container for 2 minutes before pouring the remainder of the colored water into the funnel.

What did you notice ?

The blue water fills the funnel. Some of the colored water moves out of the neck of the funnel but quickly rises to the surface.

What caused this to happen ?

Warm water is less dense than cold water. The change in density occurs because warm water expands (separate) and cold water contracts ( gets closer together). This makes a drop of warm water lighter because there are more molecules in in than a molecule of cold water. Dense cold water settles in the bottom of the bottle as it does in the ocean, while the less dense warm water rises.