# When Air Masses Collide

Use hot and cold water to simulate what happens when a warm front meets a cold one.

### Research Questions:

What happens when a warm air mass meets a cold one?

### Materials:

• Pencil and paper
• 10-gallon aquarium
• Piece of cardboard
• Scissors
• Stirrer (a wooden spoon or a ruler would be great)
• Five gallons of very cold water
• Blue food coloring
• Five gallons of very hot water
• Red food coloring
• Timer or clock
• Latex gloves
• Red colored pencil, crayon, or marker
• Blue colored pencil, crayon, or marker

### Experimental Procedure:

1. Use the pencil to draw seven large rectangles that look something like the aquarium on the piece of paper. Label the seven rectangles “0 minutes,” “1 minute,” “3 minutes,” “5 minutes,” “7 minutes,” “10 minutes,” and “15 minutes.”
2. Cut the piece of cardboard so that it just barely fits inside the aquarium, dividing it in half the short way. It should be very snug; it needs to keep the water on one side from mixing with the water on the other side for a minute or so. But don’t use any tape to keep it in place, it needs to come out easily!
3. With the cardboard snugly in place, fill half of the tank with the very cold water. (If it’s ice water, so much the better, but don’t get any ice in the aquarium.) Put a few drops of blue food coloring in the water and stir it; repeat as needed until you’re happy with the color. This is going to represent the cold front, or mass of cold air.
4. Now carefully fill the other half of the aquarium with very hot water and stir in some red food coloring. This is your warm front, or warm air mass.
5. Quickly draw a picture of what the tank looks like now by using the red and blue pencils to fill in the rectangle marked “0 minutes.”
6. Put on the gloves and quickly and carefully remove the sheet of cardboard. Try not to stir the water up too much in the process. Set the timer for one minute, remove the gloves, and watch what the water does until the timer rings.
7. Set the timer for two more minutes, then quickly draw a picture of what the water looked like at the one-minute mark in the rectangle labeled “1 minute.”
8. When the timer rings, set it for two more minutes and sketch what the tank looked like at the three-minute mark.
9. Repeat, setting the timer for the appropriate number of minutes (watch out, that changes toward the end) until you’ve filled in all of your rectangles.
10. Now look at your pictures. What did the “air masses” do? Did they mix right away? Was there a sharp division between them, or did the water combine and make a purple layer? Did the air masses stay side by side as they blended, or did one rise while the other sank? Why do you think the cold and warm fronts behaved the way they did?

Terms/Concepts: air mass, warm front, cold front

References: What’s Up? 45 Hands-On Science Experiments That Explore Weather, by B. K. Hixson, pp. 145-149 (Loose in the Lab Science Series, 2003).

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