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HEAT CONVECTION

Just when I think we've had enough of this kind of fun, we
get more! This looks like more fun than the previous project
anyway.

1. Wrap a few turns of wire around a candle, allowing enough
wire for a handle long enough to allow the candle to be
lowered into a large bottle. Light the candle and lower
it into the bottle. The candle will go out quickly
because when the air in the bottle is heated, it rises
and blocks the mouth of the bottle, preventing fresh air
from entering. Take the candle out of the bottle.

Turn the bottle upside down so that the "candle air" can
escape, and swing the bottle in the air a few times to
fill it with fresh air. Cut out a T-shaped piece of
cardboard with a stem just wide enough to fit in the neck
of the bottle. Relight the candle, and lower it into the
bottle. Quickly put the cardboard T in place, and
observe. Now light one end of a piece of rope, blow out
the flame, and, while the rope is still smoldering, hold
it first on one side of the cardboard T and then on the
other. (On the heated side, the smoke will rise; on
the cooler side, the smoke will go into the bottle.) I
don't believe this will work. Show me.

From observing the drifts of smoke, you will begin to
realize that nearly all upward and downward drafts of air
are caused in similar ways and that such differences in
temperature cause winds.

2. Put three holes in a large wooden or sturdy cardboard box
and plug the holes with corks or rubber stoppers. Over
the face of the box, attach a sheet of glass or trans-
parent plastic wrap which can act as a door. Light one
end of a piece of rope, and blow out the flame. The rope
will smolder. Place a candle in the box directly under
the top hole. Light the candle, remove any two of the
plugs, and hold the smoking rope near the lowest opening.
(The smoke will travel from the lowest opening through
the box and out a higher opening.)

The openings simulate some of the possible openings in a
room for proper ventilation, such as open chimney, open
window, a window opened at the top and bottom, or an
open door. Experiment with the box to create other air
movements. Also check your own room for comparisons.

When heat travels in this manner, it is called heat
convection. Convection ovens can be purchased for use in
your kitchens. They use less electricity than a conventional
electric range oven, and do not dry out the foods as much as
conventional ovens.


 
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