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Why Do Golf Balls Have Dimples?
為何高爾夫球上有小窩？
You're out on the golf course one pleasant afternoon. Your ball is set on the tee. You lean over the ball. You grip the club just right.
在一個舒適的下午，你站在高爾夫球場上。把球在球托上放好，身體傾斜到球的上方，握好球桿。
Your arms are straight. Your stance perfect. Whoosh! You swing, and the ball takes off toward the green, sailing in a beautiful arc–almost as if it's weightless.
你的胳膊繃直，姿勢完美。呼地一聲！你揮桿了，高爾夫球飛了起來，奔向綠地，劃出一道優(yōu)美的弧線，輕盈得似乎沒有重量。
Your impeccable technique certainly has a lot to do with the success of that drive, but you got a major assist from the little dimples on the golf ball–and they're the subject of this Moment of Science.
這一桿的成功當(dāng)然和你完美的技術(shù)密不可分，但高爾夫球上的那些小窩也幫了你的大忙-它們就是本期《科學(xué)一刻》的主題。
Combined with the proper spin, the dimples help keep the ball in the air longer, and here's how.
如果加上適當(dāng)?shù)男D(zhuǎn)，這些小窩可以幫助高爾夫球在空中停留更長時間，原因如下。
Your picture-perfect swing puts backspin on the ball. The dimples trap a layer of air next to the ball, and this layer spins with the ball.
你完美的揮桿動作使球向后旋轉(zhuǎn)。球上的小窩吸附了周圍薄薄的一層空氣，這層空氣會與球一塊旋轉(zhuǎn)。
The air being dragged across the top of the spinning ball moves in the same direction as the air that's rushing past. As the air spinning with the ball comes around the bottom it is moving in the opposite direction from the air on top, and therefore against the onrushing air. Consequently it's slower than the air on top.
球所吸附的這層空氣轉(zhuǎn)到球的上方時，它的運動方向與周圍空氣流動方向一致。而這層空氣到球下方的時候，它的運動方向與上方空氣相反，因此與周圍氣流相抵。這樣就使得下方的空氣的速度比上方的要慢。
A slow moving air stream has higher pressure than a fast moving air stream. So, the higher pressure on the bottom of the ball is going to hold the ball up longer.
速度慢的氣流壓強較大，速度快的氣流壓強較小。因此，球底部較高的氣壓可以把球向上托使它在空中駐留更長時間。
The effect of the dimples is so significant that a drive of two-hundred yards hit with a dimpled golf ball, would be shortened with a non-dimpled ball to about one hundred yards.
這些小窩的作用是十分重要的，同樣的一桿，如果可以把有小窩的高爾夫球擊出200碼，那它只能把沒有小窩的球擊出大約100碼。
