Air density has a lot to do with the weather we experience day to day! An unstable atmosphere leads to storms while a stable atmosphere usually results in a sunny day. This experiment will help to visually explain air density and how hot and cold air interact in our atmosphere.


  • 2 glass jars or cups of the same size (very important)
  • warm and cold water
  • 2 colors of food dye
  • a paper plate, baking sheet or dish
  • a sturdy piece of paper or card


  • Fill one jar with cool water and one color of food dye (blue). Fill the other with warm water and the other color (red) of food dye.
  • Place your jar of cool water on your plate or tray.
  • Place the paper or card on top of the jar of warm water and carefully flip it over.
  • Place the jar of warm water and the card on top of the jar of cool water. The card will be in-between the jars separating the water at this point.
  • Carefully pull the card out from between the jars and watch what happens!
  • Repeat the experiment and this time place the cool water on top.


Cold water is more dense than warm water! It wants to sit below the warm water. The same is true of cool air and warm air. When cool air is near the surface and warmer air is above it the atmosphere is more stable… when a cold front moves in this disturbs the balance! The cold air is dense and pushes the warm air up creating instability. This is why we often see storms ahead of a cold front. This is also the case of afternoon heating. The sun warms the air at the surface and it begins to rise because it is less dense. This creates instability and afternoon storms.