I have a pendulum.

Cool thing about pendulums: The time it takes for one to swing forward and backward—the period—won’t change, no matter how wide it swings. If it’s got a lot of energy, it’ll swing farther and faster, but the period will still be the same. This is what mechanical clocks take advantage of to keep time. That period ends up being driven by two things, and two things only: the length of the pendulum and gravity.

I pull the pendulum to one side. I release it and start the timer. I count cycles as it sways back and forth. It’s not exciting. I almost want to fall asleep, but I stay at it.

When I hit the ten-minute mark, the pendulum is barely moving anymore, so I decide that’s long enough. Grand total: 346 full cycles in exactly ten minutes.

Onward to phase two.

I measure the distance from the hatch handle to the floor. It’s just over two and a half meters. I go back downstairs to the “bedroom.” Again, the ladder is no problem. I’m feeling so much better now. That food really did the trick.

“What’s your name?” the computer asks.

I look down at my sheet toga. “I am the great philosopher Pendulus!”

“Incorrect.”

I hang the pendulum on one of the robot hands near the ceiling. I hope it’ll stay still for a while. I eyeball the distance between the robot hand and the ceiling—I’ll call it a meter. My pendulum is now four and a half meters lower than it was before.

I repeat the experiment. Ten minutes on the stopwatch, and I count the total cycles. The result: 346 cycles. Same as upstairs.

Golly.

Thing is, in a centrifuge, the farther you get from the center, the higher the centripetal force will be. So if I were in a centrifuge, the “gravity” down here would be higher than it was upstairs. And it isn’t. At least, not enough to get a different number of pendulum cycles.

But what if I’m in a really big centrifuge? One so huge that the force difference between here and the lab is so small it doesn’t change the number of cycles?

Let’s see… the formula for a pendulum… and the formula for the force of a centrifuge… wait, I don’t have the actual force, just a cycle count, so there’s a one-over-x factor involved… this is actually a very instructive problem!

I have a pen, but no paper. That’s okay—I have a wall. After a lot of “crazy prisoner scribbling on a wall”–type stuff, I have my answer.

Let’s say I’m on Earth and in a centrifuge. That would mean the centrifuge provides some of the force with the rest being supplied by Earth. According to my math (and I showed all my work!), that centrifuge would need a 700-meter radius (which is almost half a mile) and would be spinning at 88 meters per second—almost 200 miles per hour!

Hmm. I think mostly in metric when doing science stuff. Interesting. Most scientists do, though, right? Even scientists who grew up in America.