Are all shapes as strong as each other? In today's experiments we will use paper and cardboard to show that the strength of a structure is closely related to its shape. What you will need:
Four sheets of A4 paper
an A4 size hardback book
a cardboard box
EXPERIMENT ONE 實驗一
Using only paper, you will compare the load bearing ability of three shapes: a circle, a square and a triangle. Which one do you think is the strongest? 1) Make the cricle. Take a piece of A4 paper and wrap it lengthways around a soda can. Stick the ends of the paper together with adhesive tape to form a tube. 2) Make the square. Fold the piece of paper lengthways into four equal pieces. Use the adhesive tape to stick the open ends together. 3) Make the triangle. Fold the piece of paper lengthways into three equal pieces. Take the adhesive tape and stick the ends together. 4) Put a light book on top of each shape. Keep adding books until one of the shapes collapses. Which one collapsed first? 利用紙張來比較三種形狀：圓形、正方形和三角形的耐重力，你覺得那種形狀最能耐重？1.製作圓形：把一張A4大小的紙直向地環包住一個汽水罐，用膠布黏住紙張交合處，形成圓筒狀。2.製作正方形：把一張紙的長邊折成四等分，用膠布黏住兩端開口處。3.製作三角形：把一張紙的長邊折成三等分，用膠布黏住兩端開口處。4.在各個形狀上各放一本不是很重的書，然後持續疊上書本，直到其中一個形狀被壓垮。哪種形狀會先垮掉？
HOW IT WORKS 實驗原理
You should have found that the circle is the strongest, and the triangle is the weakest. In last week's experiment with eggshells we found that in a circular object, the weight is distributed evenly. Each part of the circle supports an equal amount of weight, whereas the triangle and the square have weak spots, so they collapse under a lighter load. 你應該已發現圓形是最強韌的，而三角形是最脆弱的。在上週的蛋殼實驗中，我們發現環狀物會平均分散重量。圓形的每個部份承受的重量都一樣；反之，三角形和正方形都有弱點，所以它們承受較輕的重量就會倒塌。
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EXPERIMENT TWO 實驗二
So now you know that a circular tube of paper is capable of supporting a heavy load. Now get ready to see how strong you can make a piece of paper just by folding it. 1) Take a piece of A4 paper and place it lengthways in front of you. 2) Make a 1cm fold away from you. 3) Now turn the paper over and make another fold exactly the same size. 4) Turn the paper back over and fold again, repeating until you have folded the entire sheet of paper. The paper is now corrugated. 5) Take the circular tube from the first experiment and cut it in half. Put the tubes about 10cm apart and lay the corrugated paper on top of them. 6) Put objects on top until the structure collapses. 7) Now place an unfolded piece of paper over the tubes and see how much load they can bear. 現在你知道圓筒狀的紙較能承重，現在我們要來看看經過折疊的紙耐重力有多強。1.把一張A4大小的紙直放在你的面前。2.將紙朝內折一公分。3.將紙翻面再朝內折一道和剛剛一樣寬的一折。4.翻面再折一道，重複這個步驟到整張紙都折好為止。這張紙現在應該是波浪狀。5.將上個實驗做的圓筒裁切成一半，把兩個一半的圓筒相隔約十公分放好，再把成波浪狀的紙放在上面。6.在上面放東西，直到這個結構倒塌。7.現在放一張沒有折過的紙在兩個對半的圓筒上，看看它們可以承受多少重量。
WHY IT WORKS 實驗原理
The unfolded piece of paper slipped right off the tubes even under a very light load, whereas the corrugated paper held strong. This is because the corrugation strengthens the paper and it's also because of friction. The unfolded paper is smooth and cannot grip the surface of the tubes, whereas the corrugated paper can.
EXPERIMENT THREE 實驗三
In the final experiment we'll combine elements of what you've learned in the first two experiments to see how cardboard can be strong enough to support your weight. 1) Take your corrugated cardboard box and cut off an 80cm by 15cm strip. 2) Wrap the strip of cardboard round a two liter soda bottle and tape the ends together with adhesive tape. 3) Place the book on top of the cardboard. 4) Now carefully stand on top of the book. How long can you stay standing until you fall off or the tube collapses? 最後這個實驗，我們要結合從前面兩個實驗中學到的原理，來看看厚紙板堅固到能支撐你體重的程度。1.把你準備好的波浪狀紙箱紙板裁成一條長八十公分、寬十五公分的長條。2.把這個長條環包住一瓶兩公升裝的汽水，再用膠布將兩端黏合。3.在這個硬紙板圓筒上放一本書。4.小心地站到這本書上。在你跌下來或硬紙板圓筒倒塌前，你可以站在上面多久？