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A fastball covers the distance from the mound to the plate
in less than half a second, requiring lighting reflexes and judgment from
the batter to even make contact. So when the hitter does make contact, he
has to try to make the most of it. As Brian Johnson describes it, a hitter
has to be aware of wind and atmospheric conditions to get the most out of
a hit: "Sometimes the wind might be blowing somewhat in towards the
plate in left field, and slightly out of the park in right. In that case,
you might take advantage by trying to hit the ball towards right."
The density of the atmosphere can also play a role: "In
the Colorado Rockies' new stadium, which is at altitude, they have much
thinner air. So however the thickness of the oxygen molecules is calculated,
the ball flies much farther." Under such conditions, hits that might
be routine fly balls can sail over the fence for a home run, and hitters
who might not try for home runs can suddenly think about swinging for the
fences.
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So what is it about traveling through air that affects a hit?
Say that the ball, struck by the bat, flies into the air at 165 miles per
hour, at an angle of 55 degrees. If the ball were flying through a vacuum,
the distance it would travel would be determined solely by the ability to
resist gravity imparted by its speed and trajectory, and it would travel
799 feet! Even in a baseball stadium twice as large as those which exist,
this would still be a home run. However, since we are on earth, the ball
must travel through the air. The direction and strength of the wind can
alter the ball's path, as can the relative density and humidity of the air.
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The two properties of the air that affect the ball's flight
are density and viscosity. In a dense gas or fluid, the molecules are closer
together, and an object moving through it must push aside a larger number
of molecules, which takes more energy, diminishing the distance the ball
will travel. The viscosity of a substance reflects how much it resists flowing,
and also how "sticky" it is. Substances like motor oil and honey
have high viscosity, while gasoline and benzene are examples of low-viscosity
liquids. Gases are much less viscous than fluids--about 100 times less.
The viscosity of air increases slightly as temperatures increase, but not
enough to make a noticeable difference in drag.
The density of the air changes with variations in the temperature, pressure,
and humidity of the air. As the temperature increases, the air density decreases.
Air is 12 percent less dense at 95 degrees Fahrenheit than it is at 30 degrees
Fahrenheit, resulting in markedly less drag. Density also decreases with
a drop in air pressure. As you move to higher altitudes, air pressure decreases
significantly, about 3 percent for every 1000 feet of elevation. So a moving
baseball experiences about 15 percent less drag at the 5000 foot elevation
of Denver's "Mile High" stadium than at a sea-level stadium like
Boston's Fenway Park.
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