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  3. Experienced baseball fielders can tell how far a ball is going to travel just by listening to the crack of the bat. If they didn

Experienced baseball fielders can tell how far a ball is going to travel just by listening to the crack of the bat. If they didn

admin2010-01-13  94
问题    Experienced baseball fielders can tell how far a ball is going to travel just by listening to the crack of the bat. If they didn’t, they wouldn’t stand a chance of catching it, claims a physicist in New York.
   "When a baseball is hit straight at an outfielder, he cannot quickly judge the angle of the scent and the distance the ball will travel," says Robert Adair, a physicist at Yale University. If he relied purely upon visual information, the fielder would have to wait for about one-and-a-half seconds before he could tell accurately if the pitcher hit the ball long or short. By this time the ball may have travelled too far for him to reach it in time.
   To stand a fighting chance of catching it, according to Adair, fielders must listen to the sound the ball hitting the bat to judge how far it will travel. There is anecdotal evidence to support this, he says. A former centre fielder told Adair: "If I heard a crack I ran out, if I heard a clunk, I ran in."
   To test his hypothesis, Adair calculated how quickly a fielder could change direction if he had misjudged whether the ball was going long or short. The difference between the "crack" and "clunk” can he explained by how well the batter has hit the ball, and could mean a difference in running distance of as much as 30 metres, he told delegates at a meeting of the Acoustical Society of America in Chicago last week.
   Scientists already knew that to hit a ball long the batter must strike it somewhere near the vibrational node of the bat, known as the sweet spot. Balls hit on the sweet spot generate fewer energy-sapping vibrations in the bat, allowing greater energy transfer to the ball. Conversely, mishit balls make the bat vibrate strongly and so do not travel as far.
   Adair is quick to point out that this only applies to wooden bats, which are used in major league baseball. Aluminum bats, on the other hand, tend to produce a fairly uniform "ping” sound regardless of where you hit them.
Adair points out that his theory can’t be applied to aluminum bats because ______.
选项 A、the "ping” sound is too vague for a fielder to catch
B、with the aluminum bats the batter always hits the ball stronger
C、they don’ t produce different sounds of "crack" and "clunk"
D、the sounds they produce may interfere with the fielder’s judgment
答案C
解析  Adair在最后一段指出，铅质球棒无论球击在何处发出的都是同样的一声“呼”。
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