# Swingin' physics

By Phil Plait | June 1, 2011 2:00 pm

There are four things most people don’t know, or simply don’t appreciate, about physics: 1) the right answer to a question is sometimes surprising; 2) it’s simpler than you think sometimes; 3) that simplicity can spawn terrible complexity; and 4) in simplicity, complexity, and the border in between lies great beauty.

For example, I bet if you went up to people on the street and asked them why different pendula (I prefer Latin plurals) swing with different times, they’d say it was the weight of the bob at the end. But it’s not that at all: it’s actually the length of the pendulum itself that is the major factor in determining the swing time (called the period) — the mass of the bob has nothing at all to do with it! A heavy bob and light bob will still have the same period if the length of the string is the same (try it yourself).

Surprising and simple, right? So what about the other two things, complexity and beauty? Well, here’s a perfect example of that:

Isn’t that lovely? Note the bobs are all the same, but the length of each pendulum is different; the shortest has the smallest period. Each one swings at its own pace, and as time goes on those different rates sometimes line up, giving you the gorgeous patterns. But then that breaks up and you get what looks like random motion. There are also slight variations in the period of a pendulum; friction, imperfection in the exact length used, and so on. Later in the video you can see that as the pendula don’t line up perfectly.

Do yourself a favor: watch the video again, but this time instead of watching the whole set-up move, just fix your attention on one of the bobs as it moves. You’ll get a startling change of reference as it looks like the other pendula are swinging around it. You can also watch as the ones on either side swing with longer or shorter periods, imparting the very odd illusion of what looks like communication between the bobs.

See what I mean? Simplicity, complexity, beauty, and my favorite, surprise. It’s that last that keeps a lot of scientists in the business. We get the same sense of awe and wonder that everyone gets when contemplating the mechanics of the Universe, and we get it all the time. Throw in that surprise every now and again, and you guarantee a life-long addiction to science.

Tip o’ the to Mike Lunenburg and Amanda Bauer of Astropixie (whose post reminded me I wanted to write about this as well).

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