Air Pressure and Resistance
Name: Manabu S.
I have the same qusetion as the one in your Physics
regarding air density and baseball. I understand from the answer that
pitchers' fast balls do not become faster at high altitude because the
short distance the thrown balls travel, while the thin air makes home run
balls travel further because the distance involved is much larger.
If this is the case, I would like to ask a related question. Bob
Beamon won the men's long jump at the Mexico City Olympic Games in
1968. His record, 8.92m, was so astonishingly great that it had
remained as the world record for almost a quarter of a century. It is
always explained that his record was aided by the thin air of high
altitude Mexico City. Is this really the case? If thin air affects
long jump as it has been said, why doesn't thin air help pitchers' fast
balls travel faster? The distance between a pitcher's mound and a home
plate is twice as long as long jump records. I don't know how to
calcurate relative effects of air density on different objects.
would you explain this to an ignorant man?
There is no definite way to calculate the air resistance an object will
experience. It depends too much on the shape and size of the object. Air
resistance, or drag force, tends to be proportional to the square of the
speed of the object (relative to the air). It is also proportional to the
mass density of the air. If the shape os "aerodynamic", like a plane wing
or a javelin, air resistance is less. If the front surface of the object is
large and flat, air resistance is more. Air resistance of a amooth ball is
less than that of a rough cube, provided both are about the same size and
traveling at the same speed through the same air. In addition to air
density, humidity can have an effect on certain materials.
The jumper being aided by thin air is possible. It would help more in the
initial run. The run is short enough that he wouldn't run out of breath.
His maximum speed running would be slightly higher than at lower altitudes.
This, plus a little less resistance while jumping could increase the length
of his jump by maybe 0.5 to 1.0 meters at the most. What would be his
greatest aid is slightly altering his "launch angle" to accomodate the lower
air density. I expect that noticing the effect during practice and
compensating are what gave him the most benefit.
Dr. Ken Mellendorf
Illinois Central College
I do not know the exact quantitative effect of air
density on air resistance. I do know that all moving
objects, including baseballs and long jumpers, are
effected, to some degree, by air density.
Keep in mind that Olympic records such as long jumping
are determined by minuscule values (e.g. a world
record could be broken by a mere half inch). A human
body in a long jumping position presents a large
surface that is very effected by air resistance. The
thinner air of Mexico City could have given Bob Beamon
that half inch he needed to set that record.
Although, it seems very unfair to say that thin air is
what allowed him to make that record. I was not aware
that Mexico City has thin air.
A baseball is so small that if the air were thinner,
its speed increase may not be noticed. A ball that
travels at 60 mph may go at 60.1 mph in thinner air,
but no one will notice that.
Hope this helps
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Update: June 2012