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The wind blows because air pressure is higher in one place than
in another place. The air moves from areas of higher pressure to
areas of lower pressure. Objects like buildings, trees, and hills
affect the direction of the wind near the surface. To get the best
idea of the wind direction, try to stand far away from such objects.
A park or a playing field is the best place to observe the wind.
Wind speed is measured with an anemometer. Most anemometers have
four horizontal shafts arranged like the spokes of a wheel. The
end of each shaft is cup-shaped. The wind pushes the concave side
of the cup more than the convex side, so the anemometer spins in
the wind. The faster the anemometer is spinning, the stronger the
wind.
You do not need an anemometer to estimate the wind speed. You can
use a verbal scale, called the Beaufort scale, which describes the
effect of the wind on everyday things like trees.
Wind direction is measured with a wind vane. One end of the vane
has a small, heavy object, and the other end has a flat object with
a large area. The wind pushes the flat object more than the small,
heavy objects, so the vane swings around to be parallel to the wind.
You can estimate the wind direction by yourself just by using your
face as a "sensor." Face into the wind, and then record
the direction you are facing, relative to north.
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