Spinning

When I found out I was going to the South Pole, one of the first things I wanted to do was to set up a Foucault pendulum. Someone had done it before, but to me the evidence looked slim. I didn’t feel that they had proved that the earth turns and that they were at the South Pole.

I looked into building one myself, but that seemed hard; too hard for a software guy like me.

A bit of research found a company that builds and installs pendulums for museums and science centers and such. Compred to the USAP budget, they aren’t very expensive. Compared to my budget, they are prohibitively so. There’s also a company that makes them for class-room science, and claims that the device will demonstrate the rotation of the earth in the time it takes to teach a section of physics, and for only about $500. Lots of sites sell them, but I couldn’t find out the manufacturer. I tried to get some technical specs, but couldn’t find anything, so I was a bit leery of shelling out $500 for a pig in a poke. Also, I procrastinated a lot.

My pal Simon suggested that I could also use a gyroscope to measure the earth’s spin, and pointed me at a nifty gyroscope sales site. They were out of stock, but patience — which is hard to tell from procrastination — eventually found them back in stock, and thanks to net-commerce got one ordered and on its way to South Pole.

There is a big-science project going on here now — where by “now” I mean “as soon as the equipment actually gets here” — which is using a single atom as a very sensitive gyroscope. I don’t understand the details, but they are looking for “Lorenz violations” in symmetry. And when I say I don’t understand the details, I mean I don’t understand what those words mean when strung together like that. They are so keen on being at the south pole that they are considering digging a tunnel under the path the ice moves so that they can move their experiment an inch or so each day and stay exactly over the pole itself. Talk about exclusive real estate.

The first experiment ended in what might have been disaster and damage to the gyroscope. This proved a false hope and so I felt obliged to repeat the experiment.

The Set-Up
Ideally I’d like to have the gyroscope isolated from as many other forces as possible. Simon’s initial suggestion was to secure it horizontally to a piece of styrofoam and float the whole thing in a big tub of water. It would need some anchorage to make sure it didn’t bump the sides of the tub, but a piece of string and a weight would have done that. Good idea, but not in the end what I went with. I could have co-opted the dish pit for long enough, or could have found another big tub of water. But I didn’t.

My dresser with something hanging in front of it. I think it's a gyroscope with a motor attached. Photographed on January 17th, at 8:03:30 PM in some timezone or other.

My dresser with something hanging in front of it. I think it’s a gyroscope with a motor attached. Photographed on January 17th, at 8:03:30 PM in some timezone or other.


Rather than floating, I went for the suspended option, hanging the gyroscope from the ceiling of my room with string, mostly because it seemed easier at the time. In addition to having to twist the power cord, it would have to twist the string it was hanging from. There was no friction-free swivel or anything, just string and wire hanging from a ceiling-tile brace.

My dresser, but higher up. Oh, and that's the battery pack with two dead batteries wedged into it to hold the wires from the power brick in place.

My dresser, but higher up. Oh, and that’s the battery pack with two dead batteries wedged into it to hold the wires from the power brick in place.


The gyroscope also requires power to keep spinning. It comes with a handy battery pack, taking four AAs but that only powers the gyroscope for about two hours, and while I could have set up to measure 30 degrees I didn’t — that would have been harder. So instead I added a 6 volt, 200 milliamp plug-in power brick. And that ensured that the gyroscope would be connected to the earth, so as the earth spun under the gyroscope, it would have to twist the power cord.

Results, or Lack Thereof

The gyroscope suspended in its harness, spinning, on January 18th, 2013, at 12:45:48 AM in some timezone or other. For angular reference, a fine-point Sharpie pen was added to the scenario at time zero. I have no idea why I didn't get a picture of the sharpie and pendulum at time zero. Bad scientist! No Nobel Prize!

The gyroscope suspended in its harness, spinning, on January 18th, 2013, at 12:45:48 AM in some timezone or other. For angular reference, a fine-point Sharpie pen was added to the scenario at time zero. I have no idea why I didn’t get a picture of the sharpie and pendulum at time zero. Bad scientist! No Nobel Prize!

The gyroscope suspended in its harness, spinning, on January 18th, 2013, at 5:24:25 AM in some timezone or other, a degree of precision totally unwarranted by the other equipment. To confuse things, I didn't photograph from the same angle as "During". Note Sharpie. Also note the gravity/inertia detector in the lower right. I keep one of those attached to my camera at all times.

The gyroscope suspended in its harness, spinning, on January 18th, 2013, at 5:24:25 AM in some timezone or other, a degree of precision totally unwarranted by the other equipment. To confuse things, I didn’t photograph from the same angle as “During”. Note Sharpie. Also note the gravity/inertia detector in the lower right. I keep one of those attached to my camera at all times.

Twelve hours later [technically, 15:39:05] the earth had spun a half-revolution under the experiment, as evidenced by the sun, and if the gyroscope had rotated 180 degrees relative to my room I would have called the experiment a success. Considering all the experimental error I injected into the system, I would say that the rotation was near enough zero to call it zero. Total and complete fail, but this time without any damage to the equipment. So yay me.

A Few Other Observations

Since the gyroscope is hanging from a fixed point it can be a torsional pendulum — if you twist it a bit and let it go, it untwists, twists the other way, and back again. If I did that when it was spinning, it should have a different period, since the magic gyroscopic force would resist the torsional force. I think. Then someone who knew math and physics and stuff could figure out how big that force was. I can get some science-value out of my new gyroscope.

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2 responses to “Spinning

  1. Can you put a really good bearing in the pendulum to prevent the torque from the string stopping the pendulum from not turning? The water tub thingy would to the same…

    • One could do that. But I’ve already shipped the gyroscope home. Maybe some other year.
      But there’s still the issue of getting power to it while allowing it to turn freely.

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