Frequently Asked Questions

Setup

1. Q. The wire won’t go through the wire holder. What do I do?

   A. Make sure the set screw is not in all the way. If it is, back it out a couple of turns. Try again. If it still doesn’t go in, spin the wire holder 90 degrees or so around the axis of the wire, back and forth while pushing on the wire; it should go in. If not, look at the small hole against a light, you should be able to see through it. If it still doesn’t go in, you will have to contact your dealer for assistance.

2. Q. I can’t get the unit level. Even when I turn the foot adjuster all the way to the top, the foot comes off before the tripod is level.

   A. The leveling legs are only useful on a surface that’s close to level. You either have assembled the unit incorrectly or you will have to find a more level surface.

Operation

3. Q. I start the bob swinging and then press RESET. The bob will oscillate at first but the amplitude slowly decays and eventually stops. What do I do now?

   A. Check the setup again as listed in sections 3 and 4. If it is setup properly, then check to see if the nipple is moving up and down 2 minutes after reset. If it isn’t, then you need to first check the length of the pendulum. The distance between the tip of the nipple to the middle of the bob needs to be about 1 meter, plus or minus 5% (2 inches or 5 cm). If it is not in that range, adjust the wire holder until it is. Try again. Is there a lot of vibration or movement on the floor where you have set up the pendulum? Wait until the area is quiet and then start the pendulum. If this is not possible, try moving the pendulum to a quieter location just to start it up, save the settings (see section 4.5), and return the pendulum back to this spot. If this doesn’t work, contact your dealer for assistance.

4. Q. I can get the pendulum to keep swinging, but it won’t turn with the Earth’s rotation. What can I do to get it to turn?

   A. Well, surprise, you just proved that the Earth doesn’t rotate (only kidding). There are a number of things that have to be correct for the Foucault Pendulum to turn.

   Here’s the checklist:

   1. The unit should be on a level and stable surface
   2. The unit should be leveled
   3. The windshield should be installed with the bottom of it just touching the ground. The sides should be slightly taut
   4. The unit should be installed away from heating or cooling vents, radiators or windows (no drafts and no direct sunlight)
   5. The amplitude needs to be about 2 bobs wide. A little bigger might be better in some environments. A pendulum with an amplitude that’s too big will never turn
   6. Don’t place extra objects other than the clockface inside the windshield space
   7. The bob needs to be at least 2 inches (5 cm) above the floor

5. Q. The pendulum turns but stops at a certain point and stays there.

   A. Use the answer in question #4

6. Q. The pendulum turns, slows down, or stops at a certain point, and then goes again.

   A. Use the answer in question #4

7. Q. The pendulum turns but slows down or stops at a certain time of the day, but then goes again later.

   A. This is probably due to convection currents that are generated from heating or cooling systems or sunlight. The air conditioner or heater may be running during the time of day when you are noticing the slow down or stop. Either move the unit to a more suitable place or put up something to shield the unit from these heating and cooling sources. Direct sunlight is not good for the unit.

8. Q. The bob is swinging, but it wobbles while it swings. It has behaved like this for hours. How do I stop it?

   A. You don’t have the bob, wire and wire holder setup right. The wire holder is designed to fit flat against the top of the inside of the bob. When it is assembled correctly, the wire should be coming out the middle of the hole in the top of the bob. Try reseating the wire holder in the bob.

9. Q. When I start the bob swinging, the bob twists one way and then the other. Did I do something wrong?

   A. This is normal behavior. The bob will normally twist unless you take great pains to start it with out any torque on the wire. The twisting motion will decay and stop after several hours.

10. Q. The pendulum turns at a faster or slower rate than it is supposed to according to the clockface. Can I fix this?

    A. Maybe. The pendulum’s rate of turning is affected by the environment. See answer #4 for help in making sure the setup is correct. If it is, you might still have the amplitude too high. The pendulum might be slowing down as in questions #5 and #6. There are also some unresolved physics questions about the pendulum turning slightly slower or faster when the direction of the swing points in certain directions. Also a driven Foucault Pendulum under the best of circumstances might go faster due to a quirk in the physics of driving the pendulum. See section 2 for more details.