Foucault Pendulum

[steve_bank]

Foucault pendulum - Wikipedia

en.wikipedia.org

The Foucault pendulum or Foucault's pendulum is a simple device named after French physicist Léon Foucault, conceived as an experiment to demonstrate the Earth's rotation. A long and heavy pendulum suspended from the high roof above a circular area was monitored over an extended time period, showing that its plane of oscillation rotated.

The pendulum was introduced in 1851 and was the first experiment to give simple, direct evidence of the Earth's rotation. Foucault pendulums today are popular displays in science museums and universities.[1]

Something pther than doom and gloom.

 

[Politesse]

We have just such a device at the college where I am employed, which is included in the list at your link. Ours is set in a large tower to one corner of the four story building, and it knocks over a pin each hour as it swings. As I am acquainted with many of the people involved in its construction, I know that it was no accident that they chose such a visible symbol to anchor the new science building. They see themselves as a candle in the dark, in a mostly conservative and science-skeptical county, and they are not wrong. "And yet it moves". The proof of the legitimacy of their work can be seen for miles.

 

[Elixir]

Something pther than doom and gloom.

… until it stops knocking over pins.
Then it’s doom.

 

[Politesse]

Something pther than doom and gloom.

… until it stops knocking over pins.
Then it’s doom.

No, the museum manager just resets the pins every morning before they open up shop.

 

[Elixir]

Something pther than doom and gloom.

… until it stops knocking over pins.
Then it’s doom.

No, the museum manager just resets the pins every morning before they open up shop.

I used to watch the one in GG park in San Francisco… hypnotized, wondering what if an hour came and went and the pendulum didn’t move. What then? Go outside and make sure the sun isn’t stuck in the sky?

 

[Politesse]

If the earth ceased rotation within one hour, the local pendulum would not be your first indication of a problem!

A better sci fi plot might be a situation where the pendulums of the planet all start to gradually slow and no one can figure out why...

 

[Shadowy Man]

If the earth ceased rotation within one hour, the local pendulum would not be your first indication of a problem!

A better sci fi plot might be a situation where the pendulums of the planet all start to gradually slow and no one can figure out why...

We will still know from other sources much sooner than Foucault pendulums. Probably GPS satellites first and certainly other satellites, too.

 

[Elixir]

We will still know from other sources much sooner than Foucault pendulums. Probably GPS satellites first and certainly other satellites, too.

If all the energy of earths rotation was suddenly absorbed by the earth itself, the first indicator would probably be the fact that the entire planet would be a molten ball of lava. I hate it when that happens!

 

[steve_bank]

There was one at a science center in Stamford Ct where I grew up.

I am wondering, are all those global pendulums sucking kinetic energy out of the Earth changing the weather?

 

[Shadowy Man]

We will still know from other sources much sooner than Foucault pendulums. Probably GPS satellites first and certainly other satellites, too.

If all the energy of earths rotation was suddenly absorbed by the earth itself, the first indicator would probably be the fact that the entire planet would be a molten ball of lava. I hate it when that happens!

The assumption I was responding to was that it was a gradual change.

 

[bilby]

We will still know from other sources much sooner than Foucault pendulums. Probably GPS satellites first and certainly other satellites, too.

If all the energy of earths rotation was suddenly absorbed by the earth itself, the first indicator would probably be the fact that the entire planet would be a molten ball of lava. I hate it when that happens!

Oh, no. not again.

 

[steve_bank]

Put a coil across a resistor under the pendulum and attach a magnet to the ball. When the magnet passes over the coil current is induced and shows up as heat in the resistor.

How does that affect the kinetic energy of the Earth? Albeit in a very small way, how does that chabge ripple through the solar system?

 

[Elixir]

It’s gonna slow the pendulum.

 

[bilby]

It’s gonna slow the pendulum.

And make foucault difference to the Earth.

 

[Loren Pechtel]

If the earth ceased rotation within one hour, the local pendulum would not be your first indication of a problem!

A better sci fi plot might be a situation where the pendulums of the planet all start to gradually slow and no one can figure out why...

We will still know from other sources much sooner than Foucault pendulums. Probably GPS satellites first and certainly other satellites, too.

Yeah, anything messes with gravity or Earth's rotation will be caught by the GPS guys pretty fast when their systems start returning wrong numbers. They work at extreme precision (12 digits worth IIRC) all the time and they produce even more accurate records of where the satellites actually were. (The geologists and volcanologists like millimeter precision but don't need realtime. Combine the recordings from special receivers with the actual satellite tracks and you get far more accuracy.)

 

[steve_bank]

It’s gonna slow the pendulum.

Yea. The counter electromagnetic force of the coil will oppose the field of the magnet. The mount of the coil will experience a force.

I'd think conservation would say the energy consumed in the resistor has to be reflected in a debit in KE of the Earth. If not it violates LOT, perpetual motion.

The KE of the ball comes from the KE of the Earth, or so I'd think.

 

[WAB]

Foucault's Pendulum - excellent novel by Umberto Eco. Not that that has Foucault to do with anything. Yes, stole bilby's joke.

 

[Bomb#20]

It’s gonna slow the pendulum.

Yea. The counter electromagnetic force of the coil will oppose the field of the magnet. The mount of the coil will experience a force.

I'd think conservation would say the energy consumed in the resistor has to be reflected in a debit in KE of the Earth. If not it violates LOT, perpetual motion.

The KE of the ball comes from the KE of the Earth, or so I'd think.

It can't come from the kinetic energy of the earth -- that would violate conservation of angular momentum. The energy consumed in the resistor came from whoever set the pendulum in motion in the first place, so, from the calories in his food, so, ultimately, from the sun.

 

[steve_bank]

So, at long last...perpetual motion.

Ureka! We have solved the energy problems.

As simple as the Laws Of Thermodynamics sound on the face of it they are really powerful.

Unless you reject conservation and entropy once in motion the energy for the motion of the pendulum has to come from somewhere, the energy to overcome losses in the pendulum.

Regressing back in time I imagine you end up at the BB and the old question of the possible thermal death of the universe.

Imagine a thermodynamic boudary around the pendulum. Expand it to the Earth, the solar system, and to the expanse of the universe.

Mind boggling aint it.

 

[bilby]

Unless you reject conservation and entropy once in motion the energy for the motion of the pendulum has to come from somewhere,

No, it doesn't. Conservation tells us that once in motion the pendulum will move forever without requiring any energy from anywhere. Rejecting conservation is what you must do in order to claim "once in motion the energy for the motion of the pendulum has to come from somewhere".

the energy to overcome losses in the pendulum.

Ah, now that's the exact opposite claim. You are talking about the energy for the motion of the pendulum being lost somewhere.

But it's surely not being lost to kinetic energy of the Earth - that would imply that the pendulum would be causing the Earth to speed up.

In fact, the losses are minuscule for a sufficiently large pendulum with a low-friction hinge. What little energy is lost will mostly go to warming the air that the pendulum moves through, and a little to warming the hinge.

A well designed pendulum will keep going for several hours without any energy input to replace those tiny losses; Foucault pendulums in museums usually have an electromagnet to give the pendulum a tiny extra "kick" on each swing so to replace that lost energy. That energy mostly comes from burning coal.

As an aside, the pendulum in a clock typically gets its energy to replace frictional losses via an "escapement" mechanism that is powered from the winding of a spring or the lifting of weights, which is done by human muscle power, and therefore (as @Bomb#20 points out above) ultimately from the Sun. It's an elegant design in which the clock's mechanism powers the pendulum, while in return the pendulum governs the rate at which the mechanism moves.