Grace - Centrifuge Experiment

Okay, take a breath. Let’s not jump to wild conclusions. Yes, the gravity is too high. Work from there and think of *sensible* answers.

I could be in a centrifuge. It would have to be pretty big. But with Earth’s gravity providing 1 g, you could have these rooms at an angle running around a track or on the end of a long solid arm or something. Set that spinning and the aggregate centripetal force plus Earth’s gravity could be 15 meters per second per second.

Why would someone make a huge centrifuge with hospital beds and a lab in it? I don’t know. Would it even be possible? How big would that radius have to be? And how fast would it go?

I think I know how to find out. I need an accurate accelerometer. Dropping things off a table and timing them is all well and fine for rough estimates, but it’s only as accurate as my reaction time on hitting the stopwatch. I need something better. And only one thing will do the job: a small piece of string.

I search the lab drawers.

After a few minutes, I have half the drawers open and have found just about every form of lab supplies except string. I’m about to give up when I finally find a spool of nylon thread.

“Yes!” I pull off a few feet of thread and cut it with my teeth. I tie a loop on one end and tie the other end around the tape measure. The tape measure will be playing the role of “dead weight” in this experiment. Now I just need something to hang it from.

I look above me at the hatch over my head. I climb up the ladder (easier now than ever before) and put the loop over the main latch handle. Then I let the tape measure’s weight pull the string taut.

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.

Anyway, that would be the largest centrifuge ever built…and why would anyone build it? Plus, something like that would be loud as heck. Whizzing through the air at 200 miles per hour? At the very least there’d be some turbulence here and there, not to mention a lot of wind noise. I don’t hear or feel anything like that.

This is getting weird. Okay, what if I’m in space? There wouldn’t be turbulence or wind resistance, but the centrifuge would have to be bigger and faster because there’s no gravity to help out.

More math, more graffiti on the wall. The radius would have to be 1,280 meters—close to a mile. Nothing anywhere near that big has ever been built for space.

So I’m not in a centrifuge. And I’m not on Earth.

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Chapter 2