Science in Sweatpants: Temperature, density and weather

Did you know that air is considered a fluid? It behaves almost exactly the same as water, so it’s easy to use water to illustrate things we can’t always see in the air.

With this experiment, we’ll be illustrating how air masses with differing densities interact with one another.

Here’s what you’ll need:

  • 1 flat-bottomed, see-through container (here we’re using a plastic shoebox)
  • Enough room-temperature water to fill the container up ⅔ to ¾ of the way full 
  • Approximately 1 cup of cold water, dyed blue
  • Approximately 1 cup of hot water, dyed red

For this demonstration, I cooled the water down with ice for a few minutes. For the hot water, hot water from the tap should be fine. If you want to boil water, make sure you allow it to cool for 5-10 minutes before using it.

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First, slowly pour the cold water into one side of the container. Do so gently so you don’t cause lots of ripples. What do you see the cold, blue water doing

Next, pour in the hot water to the other side of the container. Again, doing so gently.

Here’s where you really begin to see science at work! The cold water is denser so it should be sinking to the bottom of the container. The hot water is less dense so it should be rising to the surface.

This is a great way of illustrating what happens when a cold front moves in. As two air masses with different densities collide, one has to move.

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In the case of cold fronts, the warm air is forced upwards because it is less dense.

This upward motion can sometimes cause thunderstorms. As the warm air rises, eventually it will begin to cool down and the moisture will start to condense out. Clouds form first, then showers and thunderstorms.

Drylines, sea breezes, and warm fronts are also examples of air masses with different densities triggering rain and storms sometimes.

Did you try this experiment yourself? Let us know what you think! Feel free to share photos or videos and have fun!