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In class, you've learned that the earth's surface absorbs solar radiation, heats up, and transfers some of that heat to the air. The air then circulates, carrying the heat with it, by a process called convection. Convection currents are found in many places and on many scales, such as huge convection currents in the atmosphere, oceans, and even in the earth's interior. Smaller convection currents can be found in a cup of hot cocoa or a fish tank. Meteorologists usually use convection to refer to up and down motions of air. Heat gained by the lowest layer of the atmosphere from radiation or conduction is most often transferred by convection. Convection currents in the atmosphere carry the sun's heat from the warmest places on earth (like the tropics) to colder places (like the polar regions).
In the first part of this activity, you will be working with convection currents
in water. It is important to remember that water and air circulate heat by convection
in the same way. In fact both water and air can be thought of as fluids, the
main difference being that water is a much more dense fluid than air is. In
the second part of this activity, you will investigate the fluid nature of air.
PART 1: Currents in Water
Materials (per team)
Repeat the experiment with the following variations. Record and draw your observations after each variation. Make certain you start each trial with a clean saucer of water.
For the following three trials, place a cup of hot water under the center of the saucer as shown. Fill the cup almost to the top.
Trial A: Place a drop of food coloring on the bottom of the saucer in the center, over the cup of hot water. Take care not to stir the water.
Trial B: Place a drop of food coloring on the bottom of the saucer about halfway between the center and the side. Take care not to stir the water.
Trial C: Place two drops of food coloring on the bottom of the saucer, one halfway between the center and side of the saucer, the other in the center. Take care not to stir the water.
Observations and Questions for Part 1
In your lab books or on a separate piece of paper, complete the following.
PART 2: Air is a Fluid
Observations and Questions for Part 2
Answer these in your lab book or on a separate piece of paper.
When you're finished with the activity, click on Back to Teacher Guide at the top of the page.