《那些古怪又讓人憂心的問題》第43期:半空的杯子(2)
The vacuum on the left is surrounded by barriers, so air molecules can't easily get in. The water, being a liquid, doesn't expand to fill the vacuum in the same way air does. However, in the vacuum of the glasses, it does start to boil, slowly shedding water vapor into the empty space.
While the water on the surface in both glasses starts to boil away, in the glass on the right, the air rushing in stops it before it really gets going. The glass on the left continues to fill with a very faint mist of water vapor.
雖然左右兩個杯子裏的水都會沸騰，但涌入右邊杯子的空氣會在沸騰愈演愈烈之前就把它遏制住，而左邊的杯子則會繼續產生稀薄的水蒸氣。After a few hundred microseconds, the air rushing into the glass on the right fills the vacuum completely and rams into the surface of the water, sending a pressure wave through the liquid. The sides of the glass bulge slightly, but they contain the pressure and do not break. A shockwave reverberates through the water and back into the air, joining the turbulence already there.
幾百微秒後，涌入右邊杯子的空氣徹底填滿了原先真空的部分，並撞上水面，產生一道壓力波。杯子的側邊輕微突出來了一點，但還是能夠經受住壓力不至於破碎。反彈回來的衝擊波穿過杯子中的水又回到了空氣中，和空氣中已經存在的波動匯合起來。
The shockwave from the vacuum collapse takes about a millisecond to spread out through the other two glasses. The glass and water both flex slightly as the wave passes through them. In a few more milliseconds, it reaches the humans' ears as a loud bang.
真空消失產生的衝擊波會在約1毫秒的時間內傳播到另兩個杯子所在的地方，當衝擊波穿過杯子和水時，它們都會輕微地發生形變。又過了幾毫秒，人耳將聽到一聲巨響。Around this time, the glass on the left starts to visibly lift into the air.
在這個時刻前後，肉眼已經可以明顯地看出左邊的杯子飛了起來。The air pressure is trying to squeeze the glass and water together. This is the force we think of as suction. The vacuum on the right didn't last long enough for the suction to lift the glass, but since air can't get into the vacuum on the left, the glass and the water begin to slide toward each other.
空氣壓力試圖把杯子和水擠在一起，這就是我們平時所說的“吸力”。右邊杯子裏的真空持續時間不足以產生能夠擡升杯子的吸力，而由於空氣無法進入左邊杯子裏的真空區域，因而杯子和水開始相向滑動。The boiling water has filled the vacuum with a very small amount of water vapor. As the space gets smaller, the buildup of water vapor slowly increases the pressure on the water's surface. Eventually, this will slow the boiling, just like higher air pressure would.
沸騰的水只向真空區域輸入了很少量的水蒸氣。隨着水與杯子之間的空間減小，積聚起來的水蒸氣慢慢開始在水錶面產生壓強。隨着壓強的升高，沸騰的速度會減慢下來。However, the glass and water are now moving too fast for the vapor buildup to matter. Less than ten milliseconds after the clock started, they're flying toward each other at several meters per second. Without a cushion of air between them-only a few wisps of vapor-the water smacks into the bottom of the glass like a hammer.
此時水與杯子之間的相對運動速度太高，這點水蒸氣產生的壓強已經不足以產生什麼效果了。在開始不到10毫秒的時候，水會與杯子以每秒數米的速度撞到一起，隔在它們之間的沒有氣墊緩衝，只剩下那少得可憐的一點水蒸氣，水就像一把大錘子一樣砸在杯子的底部。
