Water Cycle - Atmosphere (1)
Post Lab 

   
OBJECTIVES:
  • Demonstrating the movement of air. 
  • Learning that wind is the movement of air. 
VOCABULARY:
  • air 
  • cold air
  • convection
  • hot air
  • moisture
  • wind
MATERIALS:

Students observe moisture and convection.

BACKGROUND:

Air is all around us, and moving air is called wind.  Wind is caused by cool air that moves in to replace rising warmer air.  Warmer air rises because the same number of molecules takes up more space.  Because it is less dense, the warm air floats on colder air.  

A convection oven uses the principle of moving heated air throughout the oven, which cooks evenly from the top and bottom.  A conventional stove cooks from the bottom up.

PROCEDURE:

Demonstrate the following to emphasize moisture, wind, heat, and air.

  1. MOISTURE DEMONSTRATION: Discuss the sources of water in air. Show condensation by putting a plastic bag over a plant a day before you show students. Moisture will accumulate on the plastic bag. Note that this is one reason why forests feel wetter than deserts. Breathe on a mirror to show that you can get moisture from air. 
     
  2. WIND AND HEAT CONVECTION DEMONSTRATION: Place a candle underneath one hole in the convection chamber (directions below). Place the chimneys (cardboard tubes from toilet paper rolls) over the holes. Stick pins into incense cones so that you can hang the cone in the top of the chimney opposite the candle. Light the candle. Wait a minute or so, then light the incense.

    Hot air rises over the candle and pulls in cool air. The smoke from the incense will travel through the box because the incense is at the cool air inlet. (As the incense burns down, it may get hot enough for smoke to rise from it. If this happens, replace it with a new cone.) Explain that this box shows how wind is formed. The candle is a hot area on the earth, and cool surrounding air is being pulled in.
       
  3. MAKING A CONVECTION CHAMBER:
    MATERIALS: cardboard tubes, box (small wooden is ideal), glass cover

    A convection chamber illustrates the movement of cold and hot air. Hot air rises over the candle and pulls in cool air. The smoke form the incense will travel through the box because the incense is at the cool air inlet. As the incense burns down, it may get hot enough for smoke to rise from it. If this happens, replace it with a new cone. This box shows how wind is formed. The candle is a hot area on the earth, and cool surrounding air is being pulled in.
      
  4. AIR DEMONSTRATION: Put a balloon over the top of a flask. The result will be more dramatic if the flask is cooled first. Place the flask in the hot water. The balloon will blow up.

     Ask the students why the balloon blew up. Most will say that the air came in through the rubber or glass.) Try to lead the discussion so that they figure out that the air already inside the flask expanded (got bigger) so it took up more room.

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