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Name:  Manabu S.
Status: other
Age: 40s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
I have the same qusetion as the one in your Physics archive, 12/22/99 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?


Replies:
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

-Wil Lam



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