The MythBusters aren’t really doing it wrong, but they give me a chance to talk about some physics. In the latest show, they tested the myth that two phone books with their pages alternating were indestructible. To test this, they put the two phone books together and then pulled them apart in a sort of tug of war. Here is a diagram:


Looks great, what is wrong with this? The problem is that by pulling this way, the MythBusters produces 320 pounds of force on the book – but they could have done twice that. This really goes back to the old question: Which would produce a greater tension, two horses pulling in opposite directions, or one horse pulling on a rope tied to a tree. The answer is that both tensions are the same. However, many say that the two horses create a greater tension. The likely thinking in this “two horses are more” answer is that TWO things are doing something must be greater than ONE thing doing something. This reasoning fails because if you tie a rope to a tree, it is doing exactly the same thing the other horse doing: not moving.

Why? A force explanation follows:

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