英文優美的文摘

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　　高跟鞋與腳部承受壓力的祕密

Under Pressure

壓力之下

In physics, pressure depends on the amount of force acting on a surface and on the size of the surface. The smaller the surface, the greater the pressure. Let’s say that a woman steps on your toe; she weighs 120 pounds. If she’s wearing flat shoes, you would feel the force of 120 pounds spread out over the whole heel of the shoe, maybe around 4 square inches. So the pressure would be 120 divided by 4, or 30 pounds per square inch.

物理學上，壓力大小取決於作用在表面力的大小和表面積大小。表面積越小，承受的力越大。假設一個重120磅的女人踩到你腳趾了。如果她穿的是平底鞋，你會感到120磅的壓力分散到鞋子的整個根部，大概4平方英寸。所以120磅的壓力平均分爲4份，或者每平方英寸30磅的力。

But when she steps on you with a high heel, the whole 120 pounds of force is concentrated on a heel that is maybe one eighth of one square inch in area. Now the pressure of her step is eight times as much, or 240 pounds per square inch instead of 30 pounds per square inch. Of course, it hurts more.

但如果她穿的是高跟鞋，整個120磅的力集中在或許只有八分之一英寸大小的鞋跟上。她踩下去的壓力也是8倍之多，或者說240磅每平方英寸而不是30磅每平方英寸。當然，這更痛。

It works the other way, too. SPiked heels are painful to wear because your weight is all on the spike and the ball of the foot; therefore, the pressure is much greater on these points than in running shoes, where your weight is spread out over the whole bottom of the foot.

同理，穿細高跟鞋是痛苦的，因爲你的重量全壓在在細跟和腳趾球上。因此，壓力在這些點上要比重量被分散在整個腳底的跑鞋大很多。

　　聲速測量

Measuring The Speed Of Sound

聲速測量

In the 17th century, the French scientist Pierre Gassendi knew that light traveled faster than sound. When a gun fired far away, he could see the flash of gunshot long before he heard the report.

在17世紀時，法國科學家皮埃爾·伽桑狄已經知道光速要比聲速快。遠處發生槍擊時，他看到槍的火花的時間遠早於才聽到槍響的時間。

Gassendi tried to measure the speed of sound by clocking the time that elapsed between the flash and the gunshot. Knowing the exact distance the gun was from him, he calculated that sound traveled through air at over 1,000 miles per hour. This figure is too high, though. Can you guess why?

伽桑狄試圖通過記錄看到槍的火花和聽到槍聲之間的時差來測量聲速。在知道槍支與自己所在位置的精確距離後，他計算出聲音在空氣中的傳播速度約爲1000英里/每小時。可是，這一數字過高。你能猜出爲什麼嗎?

The problem was that Gassendi relied on his own reaction time, making his measurement higher than it should have been.

問題就在於伽桑狄依賴了自己的反應時間，使得他的測量值高於實際值。

In 1864, another French scientist, Henri Regnault, devised a way to measure the speed of sound automatically, again by using a gun, but without relying on human reaction time. Regnault covered a rotating cylinder with paper, and positioned a pen to draw a line as it turned. Next, he wired the pen to two electrical circuits, placing one in front of the gun some distance away, and the second near the cylinder, threaded through a diaphragm sensitive to sound.

1864年，另一位法國科學家亨利·勒尼奧發明了一種自動測量聲速的方法，他還是用槍來測量，但是這次並沒有依靠人的反應時間。勒尼奧用白紙環繞過一個旋 轉圓筒，並在上面放置一隻筆來在紙上畫線記錄。然後，他通過電線將筆接入兩條電路中，一條電路放在槍口前的遠處某一點上，另一條放在圓筒附近，使之穿過聲 敏膜片。

When the gun fired, the first circuit broke, making the pen jump to a new position on the rotating cylinder. When the sound reached the diaphragm by the cylinder, the pen jumped back to its original position. Because Regnault knew how far the gun was from the cylinder and how fast the cylinder turned, he calculated that sound travels through air at 750 miles per hour, quite close to the speed physicists accept today.

槍響後，第一條電路斷開，筆尖會跳到旋轉圓筒的另外一個新位置上。當聲音觸發聲敏膜片後，筆會跳回原位。由於勒尼奧知道槍與圓筒的距離以及圓筒轉動的速度，於是他計算出聲音在空氣中的傳播速度爲750英里每小時，與今天物理學家普遍認同的聲速十分接近。