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CONVECTION CURRENTS

To help you understand that convection currents occur in liquids as well as gases, the following activities can be done using water.

a. Obtain a clear heat-resistant pan. Fill the pan with hot water, and place it on a heating unit. To make convection currents visible, shred some blotter paper on the water by rubbing the paper against the fine side of a food grater. Let the shreds settle to the bottom of the water. Turn on the heating unit, and make drawings of the water movements
you see.

After the water has cooled, repeat the activity. This time place the pan only partly on the heating unit. Observe and draw what you see. In both instances the warm water rises to the surface and is replaced by cooler water.

As an alternative to blotter paper, sawdust or wood shavings from a pencil sharpener can be used. Similarly, cold milk can be gently poured down the inside of a clear pan filled with warm water. If the water is quiet, the heavy cold milk will settle to the bottom. When the heat is turned on low, you will see the movements of the two liquids.

b. Obtain two identical transparent bottles, one filled with hot, highly colored water, the other with clear, cool tap water. Put a card over the top of the bottle filled with hot water. Invert the bottle, and gently place it over the other bottle. Remove the card. (There should be almost no mixing of the water in the two bottles because the heavier cold water is on the bottom.)

Now hold the bottles carefully at the very top, and reverse their positions. (The heavier cold water will quickly displace the lighter hot water.)

Your brilliant writer always believed that the water in the lake was warm at the top because the sun warmed the water. It made perfectly good sense to me that the surface water was warmer than the lower water because it was farther away from the sun.

In the water heaters at home, the hot water is at the top and the cold water is at the bottom; yet the heating unit is at the bottom. I guess hot water rises above cold water in the tanks, too. Somebody best look into this - something's missing.

 
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