Q-Eng

TED-Ed 004・・How folding paper can get you to the moon　　　　代表頁に戻る
　　　　　　　　 　（紙を折って月に行く方法）　　　　　

04分・・150wpm


(Music)
How many times can you fold a piece of paper? Assume that one had a piece of paper that was very fine, like the kind they typically use to print the Bible. In reality, it seems like a piece of silk. To qualify these ideas, let's say you have a paper that's one-thousandth of a centimeter in thickness. That is 10 to the power of minus three centimeters, which equals .001 centimeters. Let's also assume that you have a big piece of paper, like a page out of the newspaper.

Now we begin to fold it in half. How many times do you think it could be folded like that? And another question: If you could fold a paper over and over, as many times as you wish, say 30 times, what would you imagine the thickness of the paper would be then? Before you move on, I encourage you to actually think about a possible answer to this question. OK. After we have folded the paper once, It is now two-thousandths of a centimeter in thickness. If we fold it in half once again, the paper will become four-thousandths of a centimeter. With every fold we make, the paper doubles in thickness. And if we continue to fold it again and again, always in half, we would confront the following situation after 10 folds. Two to the power of 10, meaning that you multiply two by itself 10 times, is one thousand and 24 thousandths of a centimeter, which is a little bit over one centimeter. Assume we continue folding the paper in half.

What will happen then? If we fold it 17 times, we'll get a thickness of two to the power of 17, which is 131 centimeters, and that equals just over four feet. If we were able to fold it 25 times, then we would get two to the power of 25, which is 33, 554 centimeters, just over 1,100 feet. That would make it almost as tall as the Empire State Building. It's worthwhile to stop here and reflect for a moment. Folding a paper in half, even a paper as fine as that of the Bible, 25 times would give us a paper almost a quarter of a mile.

What do we learn? This type of growth is called exponential growth, and as you see, just by folding a paper we can go very far, but very fast too. Summarizing, if we fold a paper 25 times, the thickness is almost a quarter of a mile. Thirty times, the thickness reaches 6.5 miles, which is about the average height that planes fly. Forty times, the thickness is nearly 7,000 miles, or the average GPS satellite's orbit. Forty-eight times, the thickness is way over one million miles. Now, if you think that the distance between the Earth and the Moon is less than 250,000 miles, then starting with a piece of Bible paper and folding it 45 times, we get to the Moon. And if we double it one more time, we get back to Earth.