hot air balloon
HOT AIR! Design +
build + fly a hot-air
balloon to lift a weight.
The better designed
the balloon is, the
more weight it will be
able to lift.
Why do hot air balloons rise up? Hot air balloons rise because they
are filled with air hotter than the air around them, and hot air is lighter than cold air. Why is hot air lighter than cold air? When a material
is heated, its molecules absorb the heat or energy and with this extra
energy are able to move around at greater speeds.
In objects that can stretch and expand, molecules with extra energy
can move farther apart. When the molecules move, the object grows
in size or volume. It doesn't change in weight, though, because the
number of molecules doesn't change. It is made of the same number
of molecules, just located farther apart. This makes the object less
dense, but maintains its weight.
When we start heating the air of a hot air balloon, the air molecules
start moving around with more energy. As the hotter air expands,
the balloon expands, but its weight does not change right away.
Once the balloon has expanded as far as it can, then the energetic
molecules start escaping out of the hole at the bottom. This leaves
less molecules inside, making the balloon lighter than the cooler air
around it. The balloon rises.
collect
poster board (1 sheet)
tissue paper (10-12 sheets)
glue stick
scissors
ruler
piece of wire to shape into a ring
string
hair dryer
experiment
1. Draw and cut a template for the hot air balloon side panels out of
the poster board. You will use this to make tissue paper cutouts
of the same size. Draw the typical shape you see in modern balloons or try creating new shapes you would like to test.
2. Using your template, cut 8 tissue paper side panels.
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MAKING MACHINES out of paper and sticks
3. Glue the panels together into a balloon shape.
4. Cut out a circular piece of tissue paper to cover the top of the
hot air balloon and glue it on.
5. Cut some wire coil and shape into a circle.
6. Place the coil at the bottom of the balloon, fold over the tissue
paper over it, covering it, and glue it in place.
7. Make a basket out of the poster board and attach it with string or
tape to this coil ring, and place a weight in the basket.
8. Heat up the balloon with the hair dryer, let it go and watch it rise!
How do you think the size of the balloon affects how much
reflect
weight is in the basket? Why do you think size makes a difference? Does shape make a difference? Look at early balloon
designs. Try them out and see if a particular shape is better
at carrying more weight. What are you proud of learning?
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