Science | Science Experiment of the Week 9 | 291 - Paper Rope

This week's experiment is an interesting look at the properties of materials and shows why product testing is so important. You may be amazed how strong this paper rope is.

This Week's Experiment - #291 Paper Rope

These experiments are from Robert Krampf - The Happy Scientist

This week's experiment is one that occurred to me a while back and has been sitting in the file waiting for a week when nothing else jumped out at me. It is an interesting look at the properties of materials and shows why product testing is so important. You will need:

several paper towels
water

Tear two paper towels from the roll. Place one on top of the other. Start at one edge and roll the paper towels into a tight roll. Holding one end of this roll, twist the other end and keep twisting until the entire roll is twisted. You now have a short piece of rope, made from paper towels.

Now, how strong do you think a paper rope would be? Test it and see. Pull on the ends, trying to break the rope in the middle. Unless you are pretty strong, you will probably not break the rope. You may be amazed how strong this paper rope is.

How can it be so strong? Think about what paper is made from. Wood! Wood is quite strong, right. To make paper, the wood is made into a pulp of wood fibers. This pulp is rolled out to form paper. Usually, the fibers wind up aligned in the same direction. That is why a newspaper will tear easily from top to bottom, forming long strips of paper. If you try to tear a sheet of newspaper from side to side, you will have a much harder time getting long, thin strips.

As you twist the paper towel, you wind these wood fibers together and it makes quite a strong rope. Then why don't we use paper ropes? They would be cheap, light weight, and easy to make. You could make a fortune, right? To find out how good that idea really is, dip the center of the paper rope into a glass of water and then pull the ends again.

What happened? The rope broke easily. The water flowed into the spaces between the wood fibers. Since the fibers are short, the water lubricated them enough so that they could slip past each other and the rope broke. The ropes we use are made with long fibers, so they will keep most of their strength, even when they are wet.

If you watch much television, you have probably seen commercials for stronger paper towels, which keep their strength, even when wet. If you wanted to make a paper towel that was stronger when it was wet, what would you do? Add longer fibers to the paper, right? Longer fibers would not slip easily past each other when they got wet, so the paper towel would be stronger. Even so, the fibers are still short enough that it would not make a good rope, so don't try to use a roll of paper towels as an emergency rope. Otherwise, you might wind up in the Emergency Room at the hospital.

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