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Relatively speaking, air which is moving
exerts low pressure, and air that is still exerts high
pressure. This was discovered in the late 1700's by
a scientist named Daniel Bernoulli. And it is because
of this discovery that we can make wings that create
lift and make an airplane fly. As the wing slices through
the air, the air molecules moving over the top of the
wing must make it to the other side at the same time
as the molecules under the wing. Because the wind is
curved on top, those molecules have further to go and
must move faster. The combination of low pressure on
top and high pressure below work together to create
an upward push called "lift".
Try this
experiment to illustrate this concept:
Materials
List:
2 toy balloons, equally inflated
2 strings, about 1 foot long each
Tie the strings
one to each balloon. Hang or hold the balloons about
1 inch apart. Have another student blow gently between
the two balloons.
The balloons
will be "pushed" together. Remember the pressure
will be lower between the two balloons while you are
blowing air through (because moving air has less
pressure) The pressure on the sides of the balloons
is higher, because that air is moving.
What happens
when:
1- You blow even harder between the two balloons?
2-You blow the balloons from the side?
3- You stop blowing altogether?
Think about how this concept applies
to weather systems. Would you think that an area of
low pressure in a weather report would tend to be more
windy or more calm? What about an approaching high pressure
system?
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