Foucault Pendulum

This is a video compilation of a Foucault pendulum in action at the Houston Museum of Natural Science. The rotation of the plane of the pendulum's oscillations demonstrates that the earth is a rotating reference frame. The number of rotations it makes in one day (about 180 degrees in 24 hours) also indicates the latitude of the museum (about 30 degrees north of the equator).

By my count, there must be exactly 144 pins forming a circle on the floor underneath the pendulum. In the video, you will see two pins get knocked over, 1 hour apart. There was another pin between these two that gets tipped over, but this event is not on the video.

With this data, I expect the time for two adjacent pins to get knocked over to be 48/144 = 0.33 hours. Between the 3 pins getting knocked over, it should have taken only 40 minutes, not 1 hour. Perhaps the spacing or position of the pins were uneven?

At latitude L in the northern hemisphere, the plane of the pendulum's oscillations rotates clockwise by the amount 360*sin(L) degrees in one day. One can google to find out how this expression can be obtained, but let me point out two illuminating remarks regarding this expression: (1) It is the projection of the angular velocity of the earth (magnitude 360 degrees per day) onto the vertical direction at latitude L. (2) It is related to the net rotation of a vector resulting from parallel transport along a closed circuit on the surface of a sphere. This rotation is given by the solid angle subtended by the surface enclosed by the circuit. In the case of our pendulum, the circuit is the circle of latitude. We get 360*sin(L) after subtracting 360 from the solid angle subtended by the surface enclosed by the circle of latitude and that includes the north pole.

The museum is at latitude 29 deg 46 min N, according to the touch-screen panel near the pendulum. My old Magellan handheld GPS reported coordinates of 29 deg 43.281 N, 95 deg 23.353 W, 23 ft, which is pretty close. Plugging L~30 deg into our formula, we get 360*sin(30)=180 deg/day.

Other facts I learned from the touch-screen:
Pendulum weight - 180 lbs (81.6 kg)
Length - 61.6 feet (18.8 m)
Period - 8.71 sec
Swing angle - 5 deg
Displacement - 65 inches (1.65m)

Category:

Science & Technology

Tags:

• Foucault
• Pendulum
• Houston
• Earth
• rotation
• physics

[fergman90000]

hi, i have a question, what keeps it moving, should it eventually stop swinging because of friction & air resistance?? just wondering, thanks

[maxwellsdaemon7]

@fergman90000 Good question. There is an electromagnetic mechanism at the top that gives the pendulum a periodic "tug", to keep it from slowing down.

[jorge210594]

hi, i have a doubt. i wanted to know in what or where can we find a foucault pendulum...i have searched and realized that the largest ceiling clock is a foucault pendulum and also it is used in seismographers, but i wanted to know in what else...please answer me back as soon as possible

[maxwellsdaemon7]

@jorge210594 Hi there. I guess you can think of a foucault pendulum as a large ceiling clock. The foucault pendulum is special though, because it has to pivot freely at the top, such that the plane of the pendulum's swing can rotate around the vertical. I am not aware that foucault pendulum is used in seismographers.

[1D0N]

I'm no physics expert, so this is why I ask this: What I don't understand is how the plan in which the pendulum swings changes like it does. I know earth rotates of course, but the point the pendulum is hanging from, is fixed, just like the floor with the pins. My guess is this only works if the cable is fixed to the ceiling in such a way it can freely rotate around it axis. Otherwise it could never swing freely,

[maxwellsdaemon7]

@1D0N Your guess must be right.

[almalinda06]

I love this, but I have one question--can anyone tell me how the pendulum keeps moving through out the entire 24 hours? I mean, doesn't it lose momentum, slow down? And they can't exactly give it a push, because it would ruin the integrity of the 'experiment' right? Because that would probably alter the pendulum's course... Unless its oscillations are mechanical? Sorry if this is stupid, I just honestly don't know..

[maxwellsdaemon7]

Good question. The oscillation is sustained by an oscillating magnetic field applied near the top. For the rotation of the plane to truly reflect the rotation of the earth, the magnetic field can only be applied so as to sustain the oscillation in the plane of the pendulum's swing, not to make the plane itself rotate, which is what I believe is the case with all Foucault pendulums.

[memanous]

this is the gayest science experiment ive ever seen

[thewiredrabbit]

@jorge210594 If you really want to see about buying one, contact the California Academy of Sciences. We still manufacture them.510-215-0446

[LordTharrion]

@1D0N It is suspended from a bearing in the cieling which does precisely as you have assumed

[SpasticatedCunt]

FAKE

[migencluz]

@1D0N it is just a piece of string. Imagine tying a marker to a string and place it on top of a piece of paper. Swing it as you rotate the paper slowly... that is how I remember it.

[BigLebowski2000]

I know on the North Pole it's 15 degrees p/h and more to the south it swings slower, on the equator it stands still, and then further south it swings again but in the opposite direction. On the poles it takes 24 hours (a little less) to make a perfect circle, but in paris it's 30 hours or something. But in paris a days also is 24 hours so? That's the part I don't understand. I am no physics expert, so please can someone explain me (in simple words, lol) why this is? Thanks ;-)