Fri, May 23, 2008 page20

• A glimpse at surface tension 淺談表面張力

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  (MICHAEL KEARNEY, STAFF WRITER)

  Today we’re going to do three simple experiments that have to do with surface tension and water. You might be surprised at some of the results!

  What you will need:

  

  照片︰MICHAEL KEARNEY

  PHOTO: MICHAEL KEARNEY, TAIPEI TIMES

  A cup

  Water

  Coins

  Paperclips

  A paper towel or some tissue

  Dish detergent

  Aluminum foil

  A sink

  A plug for the sink

  （翻譯：袁星塵）

  今天我們要做三個簡單的實驗，這些實驗和表面張力及水有關，部分實驗結果可能會讓你感到意外喔！

  所需材料︰

  一個杯子

  水

  銅板

  迴紋針

  廚房紙巾或面紙

  洗碗精

  鋁箔紙

  水槽

  水槽塞子

  EXPERIMENT ONE 實驗一

  ► Fill the cup to the very top with water. The water should be flat and look like it’s about to overflow.

  ► Guess how many coins you can add before the water overflows.

  ► Now start adding coins one by one. Drop the coins in carefully. You don’t want to disturb the water too much.

  ► How many coins did you add? Was your guess close? How does the surface of the water look?

  ►在杯中裝入滿滿的水，杯口的水面應該平平的，並且看起來像要滿出來的樣子。

  ►猜猜看你可以投入多少枚銅板而不讓水溢出來。

  ►開始把銅板一枚一枚放入杯中；小心地把銅板放進去，不要過於攪動水面。

  ►結果你放進多少枚銅板？結果你猜得準嗎？杯口的水面看起來如何？

  EXPERIMENT TWO 實驗二

  ► Fill a cup about three-quarters full with water. Drop in a paperclip. What happens?

  ► Now tear off a small piece of the paper towel. Put a paper clip on top of it and carefully place it on the water surface.

  ► Wait for the paper towel to be saturated with water. It should sink to the bottom. If it doesn’t, give it a slight nudge with the tip of a pencil or some other pointy object. Be careful not to disturb the paperclip.

  ► The paperclip should float on the surface.

  ► Add a drop or two of soap to the water. Don’t hit the paperclip. What happens?

  ►在杯中倒入四分之三滿的水，並投入一根迴紋針，會發生什麼事？

  ►撕下一小塊廚房紙巾，再把一根迴紋針放在紙巾上，然後小心地將其舖放在水面上。

  ►等紙巾被水浸濕後應該會沉到杯底；如果沒有沉下去，可以用鉛筆筆尖或其他尖頭的東西輕推一下，但小心不要動到迴紋針。

  ►迴紋針應該會浮在水面上。

  ►在水裡加入一兩滴洗碗精，但不要碰到迴紋針。會發生什麼變化？

  EXPERIMENT THREE 實驗三

  ► Fill the sink about halfway full of water. Make sure there’s no soap in the sink.

  ► Make a small boat using the aluminum foil. Place the boat in the water. Wait for it to stop moving.

  ► Drop a few drops of water behind the boat. What happens?

  ► Now try dropping a few drops of soap behind the boat. What happens?

  ►在水槽裡裝入約半滿的水。確認水槽裡沒有清潔劑。

  ►用鋁箔紙做一艘小船，把鋁箔小船放到水中，並等它靜止不動。

  ►在小船後面滴幾滴水，會發生什麼事？

  ►試著在小船後面滴幾滴洗碗精，會有什麼變化？

  For your information

  What’s the Science? 科學原理

  The term “surface tension” is used to describe the tendency of liquid molecules in contact with a gas to “stick” together. Surface tension causes liquids like water to form a sort of skin at their surfaces. When you added coins to the water, did you notice the water ends up having a curved surface before it overflows? That curved surface forms because of surface tension — the water “sticks” together rather than overflows. 「表面張力」是指與空氣接觸的液體分子間的「內聚」特性，表面張力會讓液體（如：水）在其表面形成一層薄膜。當你把銅板放入水中，你發現水在滿出來之前，它的表面是呈圓弧狀嗎？這個圓弧表面就是因為表面張力而形成──水「內聚」而非溢出。 The paperclip is denser than water, so it should sink. But when you carefully placed it onto the surface of the water, it floated. The surface tension holds it up. The soap drops you added to the water broke the surface tension and caused the paperclip to sink. 迴紋針的密度比水大，所以它會沉入水中；但當你小心地將其放置在水面上時，它會漂浮在水面，這是因為表面張力支撐的關係。你滴入水中的洗碗精破壞了原本的表面張力，所以迴紋針會下沉。 When you dropped drops of water behind the boat, not much happened. The water doesn’t break the surface tension. But when you added drops of soap, the boat moved forward. The surface tension behind the boat was broken, so the surface tension in the water in front of the boat pulled it forward. 當你在小船後方滴入水滴時，不會有太明顯的變化，因為水滴不會破壞原本的表面張力；但當你滴入洗碗精時，小船會往前漂動，這是因為小船後方的表面張力受到破壞的關係，所以小船前方水面的表面張力會吸引小船前進。

  For your information

  Bonus 你知道嗎

  Some insects, like the water strider, are able to stand and move on top of water because of surface tension. The bugs are very light, so when they stand on water, they only slightly dent the surface and their legs repel each other. That repulsion lifts their bodies. A group of scientists at Carnegie Mellon University in Pittsburgh, Pennsylvania, studied insects like water striders and then built a small robot using ultra-lightweight carbon fiber that is also able to walk on water. But they still have some improvements to make — they said the water strider is able to move about 20 times as fast. 有些昆蟲（如水黽）能在水面上站立和移動，就是因為表面張力的關係。這類昆蟲很輕，所以當牠們站在水上時，只會讓水面產生些微凹陷，而且牠們的腳對水有排斥作用，這種斥水性足以支撐牠們身體的重量。 賓州匹茲堡的卡內基美隆大學有一群科學家在研究水黽等昆蟲的構造後，利用超輕的碳纖維製作了一個也能在水上行走的小型機器人，但他們仍有一些尚待改進的部分──他們表示，水黽在水面上移動的速度比這機器人快上約二十倍。

  For your information

  VOCABULARY 今日單字

  1. surface tension n. 表面張力 (biao3 mian4 zhang1 li4) 2. overflow v.i./v.t. 溢出 (yi4 chu1) 3. saturated adj. 滲透的 (shen4 tou4 de5) 4. nudge n. 輕推 (qing1 tui1) 5. water strider n. 水黽 (shui2 min3) 6. dent v.i./v.t. 使凹下 (shi3 ao1 xia4) 7. repel v.i./v.t. 互相排斥 (hu4 xiang1 pai2 chi4) 8. carbon fiber n. 碳纖維 (tan4 xian1 wei2)
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