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The next time you're driving during a rain shower, glance back at the rear window. You'll notice that while raindrops batter the front windshield, they seem to avoid the back window as long as the car is moving. How is that possible?
下一次下陣雨而你在開車的時候，看一看后窗玻璃。你會注意到在汽車行駛的過程中，雨滴會連續打擊到前面的擋風玻璃上，但是后窗玻璃上則不會出現這樣的現象。是什么導致這樣的現象發生呢？
When a car is moving at normal highway speed, air flows around it, from front to back. Since air can not go through the glass, when it hits the front window it suddenly changes direction and travels up and over the windshield. A raindrop, however, which is denser than air, falls from the sky with enough velocity so that it cannot be swept up and over the glass by the wind.
當 一輛汽車以正常的速度在高速公路上行駛時，空氣漂浮在它周圍并且從前往后流動。因為空氣并不能穿過玻璃，當它撞擊到前方的玻璃上時，它的方向會發生改變， 它會沿擋風玻璃往上運動。然而，由于雨滴的密度比空氣大，加之它以足夠的速度從天空中滴落下來，所以不會被吹過玻璃的風清除掉。
When raindrops approach the front windshield, they are too heavy and are going too fast to suddenly change direction and be swept up and away from the glass. Instead they burst through the wind stream and hit the windshield.
當雨滴到達前面的擋風玻璃時，它們太重并且速度太快以至于不能夠突然改變方向，也就不會被清除掉了。相反，它們沖破流風，打在擋風玻璃上。
Raindrops do tend to miss the back window, however. Wind passing over the rear of the car is accelerated on a downward angle, flowing parallel to and just above the rear window. In this case the velocity of the falling raindrops carries them into the downward flow of the wind, where they skim over the surface of the window without touching it.
然而，雨滴卻不會打到后窗玻璃上。風通過后窗玻璃時會加速往下并在后窗上方平行流動。在這種情況下，落下的雨滴的速度將它們帶入向下流動的風中，于是它們就會掠過窗戶表面而不會碰到它。
Because the wind is flowing down instead of up, the rain does not have to change direction when it encounters the wind stream. Although the raindrops are still heavier than air, the fact that the wind and rain flow in the same direction enables the wind to sweep the rain away from the window.
因為風是往下而不是往上流動，所以當雨滴碰到流風時，它們不需要改變方向。雖然雨滴還是會比空氣重，但是風和雨滴運動方向一致使得風將雨滴吹離玻璃。
