What you need:

• Two Plastic drink bottles 
• Permanent flip-tip
• pen
• Water
• Measuring cup

  Step1: Use a measuring cup to pour exactly the same amount of water into each of the plastic bottles. 

Step2: Mark the level of the water on the side of each bottle with a permanent flip-top pen. 

Step3: Place one bottle in the freezer and the other at room temperature in a place where it is not too warm. Leave them overnight.

Step4: Take the bottle from the freezer and look at the different levels.