Question about the Foucault's Pendulum?

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Question about the Foucault's Pendulum?
« on: June 11, 2020, 11:27:44 AM »
What is the swing of the Foucault pendulum, has to do with the rotation of the earth?

Foucault demonstrated the earth’s rotation via his famous pendulum. He suspended a 28-kilogram (62 lb) brass-coated lead bob with a 67-meter long (220 ft) wire from the dome of the Pantheon, Paris – Wikipedia

Here is the animation of Foucault's Pendulum.

https://upload.wikimedia.org/wikipedia/commons/8/82/Foucault-rotz.gif

Let mark a point “A” on the outer diameter (big enough) of the wire of Foucault's Pendulum, facing exactly west or any other specified direction. 

The wire of Foucault's Pendulum doesn’t spin during swinging in the experiment. It can be observed easily in the above animation – Right. It is the earth, which spins, not the wire of the pendulum. After 24 hours or more

Point “A” is also seen by the north, east, and south of the earth if the green trace in the above animation shows the path of the pendulum bob over the ground (a rotating reference frame).

I may be wrong but I suspect the force that sat the swing of the Foucault pendulum might not be in the perfect direction. The density of bob also affects the direction of the applied force.

Because

If the aforementioned experiment really shows the evidence of rotation of earth then we can also get the same result from the following experiment as well.

– Simply, here we don’t need the swing of the pendulum.
 
Let both the wire and the bob of the aforementioned experiment are at rest and don't rotate. Attached a laser light torch to the bob of the aforesaid pendulum such that it shines a laser light exactly toward the west (in a straight line) perpendicular to the above said 67-meter wire. OR it can be any mark on the wire or bob facing in a specified direction.

Remember: The wire used in the experiment of Foucault's Pendulum doesn't spin during swinging. 

After 24 hours or more

The laser light, in this case, is not seen by the north, east, and south of the earth - I believe.

What do you think?

Your comments, please!!!

« Last Edit: June 12, 2020, 04:40:20 AM by E E K »

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JJA

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Re: Question about the Foucault's Pendulum?
« Reply #1 on: June 11, 2020, 12:28:48 PM »
What is the swing of the Foucault pendulum, has to do with the rotation of the earth?

Foucault demonstrated the earth’s rotation via his famous pendulum. He suspended a 28-kilogram (62 lb) brass-coated lead bob with a 67-meter long (220 ft) wire from the dome of the Pantheon, Paris – Wikipedia

Here is the animation of Foucault's Pendulum.

https://upload.wikimedia.org/wikipedia/commons/8/82/Foucault-rotz.gif

Let mark a point “A” on the wire of Foucault's Pendulum, facing exactly west or any other specified direction. 

The wire of Foucault's Pendulum doesn’t spin during swinging in the experiment. It can be observed easily in the above animation – Right. It is the earth, which spins, not the wire of the pendulum. After 24 hours or more

Point “A” is also seen by the north, east, and south of the earth if the green trace in the above animation shows the path of the pendulum bob over the ground (a rotating reference frame).

I may be wrong but I suspect the force that sat the swing of the Foucault pendulum might not be in the perfect direction. The density of bob also affects the direction of the applied force.

Because

If the aforementioned experiment really shows the evidence of rotation of earth then we can also get the same result from the following experiment as well.

– Simply, here we don’t need the swing of the pendulum.
 
Let both the wire and the bob of the aforementioned experiment are at rest and don't rotate. Attached a laser light torch to the bob of the aforesaid pendulum such that it shines a laser light exactly toward the west (in a straight line) perpendicular to the above said 67-meter wire. OR it can be any mark on the wire or bob facing in a specified direction.

Remember: The wire used in the experiment of Foucault's Pendulum doesn't spin during swinging. 

After 24 hours or more

The laser light, in this case, is not seen by the north, east, and south of the earth - I believe.

What do you think?

Your comments, please!!!

You won't get any results without it swinging.

The bob and line never rotate during a Foucault's Pendulum experiment either.  The bob always faces in the same direction.

What we are observing is the direction of the swinging changing. Or more accurately, the Earth rotating while the direction of the swing stays the same.

The Foucault's Pendulum experiment has nothing to do with the line twisting, it's that back and forth swing with all that momentum that is staying still while the Earth rotates.

So without the motion, you won't observe anything.

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rabinoz

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Re: Question about the Foucault's Pendulum?
« Reply #2 on: June 11, 2020, 03:50:17 PM »
What is the swing of the Foucault pendulum, has to do with the rotation of the earth?
Plenty because without the "swing of the Foucault pendulum" there is nothing to define an absolute direction.

Quote from: E E K
If the aforementioned experiment really shows the evidence of rotation of earth then we can also get the same result from the following experiment as well.

– Simply, here we don’t need the swing of the pendulum.
In principle, if you could start with a perfectly suspended massive bob stationary over the North Pole it would stay stationary as the Earth rotated under it.

But there are two problems here:
  • There is nothing to define any absolute fixed direction in space for the initial positioning of the bob and
  • no support for such a massive bob could be sufficiently free of friction.

Quote from: E E K
Let both the wire and the bob of the aforementioned experiment are at rest and don't rotate. Attached a laser light torch to the bob of the aforesaid pendulum such that it shines a laser light exactly toward the west (in a straight line) perpendicular to the above said 67-meter wire. OR it can be any mark on the wire or bob facing in a specified direction.

Remember: The wire used in the experiment of Foucault's Pendulum doesn't spin during swinging. 

After 24 hours or more

The laser light, in this case, is not seen by the north, east, and south of the earth - I believe.

What do you think?

Your comments, please!!!
It is the initial swing of the pendulum that gives the reference direction.

Re: Question about the Foucault's Pendulum?
« Reply #3 on: June 12, 2020, 02:21:40 AM »
Both scenarios should give the same result because both the bob and the wire of the Foucault's Pendulum always face in the same direction and never rotate in each case.

I want to know more about the POINT at which the wire of the pendulum is suspended. Therefore can somebody explain if it is a special suspension - I mean how it possible that the rotation of the earth doesn't have any effect on the suspension of the wire of Foucault's Pendulum if it doesn't rotate or twist during swinging.

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rabinoz

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Re: Question about the Foucault's Pendulum?
« Reply #4 on: June 12, 2020, 03:37:56 AM »
Both scenarios should give the same result because both the bob and the wire of the Foucault's Pendulum always face in the same direction and never rotate in each case.
These are both much simpler if centred on the North Pole.

There is no way to fix the direction the bob is facing without first assuming that Earth is rotating once in about 23 hours and 56 minutes.

But the initial swing of the pendulum defines an initial direction and if the top support has low enough friction the plane of the pendulum's swing will remain unchanged.

Quote from: E E K
I want to know more about the POINT at which the wire of the pendulum is suspended. Therefore can somebody explain if it is a special suspension
The suspension is very important and should apply no torque (twisting) to the pendulum so various types of universal and point bearings have been used but no bearing is perfect.

Quote from: E E K
I mean how it possible that the rotation of the earth doesn't have any effect on the suspension of the wire of Foucault's Pendulum if it doesn't rotate or twist during swinging.
As above all that can be done is minimise the effect of that "twisting".

So very heavy bobs are used with long wires so that the period is very long.
Another problem is that the without a drive the pendulum will gradually stop swinging.
But the drive must be one that doesn't affect the direction of swing.

This is from a description of the large Foucault Pendulum that used to be at the Smithsonian's National Museum of American History.
Quote
Smithsonian: Foucault Pendulum
Any pendulum consists of a cable or wire or string and a bob. For a pendulum to easily demonstrate the Foucault effect, it should have as long a cable as possible (this one is 52 feet) and a heavy symmetrical bob (this one is hollow brass, weighing about 240 pounds). Like all pendulums this one loses a bit of energy with each swing due to friction from air currents and vibrations in the cable and other factors. Thus, left to itself the pendulum would swing in shorter and shorter arcs until after a few hours it will decrease almost to zero. To keep the Foucault Pendulum going, one must replace the energy lost with each swing. This can be done by giving the pendulum a little "kick" with each swing.

To do this, two iron collars are attached to the cable near the top. There is a doughnut-shaped electromagnet built into the ceiling, and the iron collar swings back and forth inside the hole of the doughnut. When the pendulum cable reaches a particular point in its swing, it is detected by an electronic device and the magnet is turned on at just the right time to give the collar (and thus the cable and the bob) a little "kick" in the exact direction of its natural swing. This restores the energy lost during the swing and keeps the pendulum from stopping. It has no effect on the direction of the swing, and thus does not interfere with the demonstration that the earth is rotating.

Re: Question about the Foucault's Pendulum?
« Reply #5 on: June 12, 2020, 05:05:25 AM »
Quote
But the initial swing of the pendulum defines an initial direction and if the top support has low enough friction the plane of the pendulum's swing will remain unchanged.

Sorry but the initial to and fro motion of the pendulum has nothing to do with changing the facing direction of point "A" marked on the outer diameter (big enough) of the wire  – quite clear in words and in animation. Unless I'm conceiving it wrong.

Point A on the outer surface of the wire always faces in the same direction whether the pendulum is at rest or swinging.



Re: Question about the Foucault's Pendulum?
« Reply #6 on: June 12, 2020, 11:09:42 AM »
How about the idea of using a drone instead of suspending the Foucault's Pendulum from the dome which is in question!

Would we be able to get the same result for the evidence of earth’s rotation if suspend a modified version of Foucault's Pendulum from the bottom of drone which can hover for a couple of hours at one fixed point in a closed environment?

Source: internet: "Given that your average drone can hover for around half an hour, the four hours, 40 minute record claimed by Spanish drone manufacturer Quaternium is pretty darn impressive"

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JJA

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Re: Question about the Foucault's Pendulum?
« Reply #7 on: June 12, 2020, 11:31:09 AM »
How about the idea of using a drone instead of suspending the Foucault's Pendulum from the dome which is in question!

Would we be able to get the same result for the evidence of earth’s rotation if suspend a modified version of Foucault's Pendulum from the bottom of drone which can hover for a couple of hours at one fixed point in a closed environment?

Source: internet: "Given that your average drone can hover for around half an hour, the four hours, 40 minute record claimed by Spanish drone manufacturer Quaternium is pretty darn impressive"

Drones can't carry much weight at all, and the constant corrections and drifting would overwhelm any subtle forces from the earths rotation.

Re: Question about the Foucault's Pendulum?
« Reply #8 on: June 12, 2020, 11:41:30 AM »
Quote
Drones can't carry much weight at all, and the constant corrections and drifting would overwhelm any subtle forces from the earths rotation.

I mentioned a modified version so it can be a simple plumb bob with a long wire either stationary or swinging at the dome of the Pantheon, Paris, or ideally at north pole.
addendum:
Using Foucault's concept, we don't need any pendulum in case of using a drone because the four or multiple sides/ faces of the drone are enough for the evidence of earth's rotation if it hovers at one fixed point for a couple of hours. 
« Last Edit: June 12, 2020, 12:10:49 PM by E E K »

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JJA

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Re: Question about the Foucault's Pendulum?
« Reply #9 on: June 12, 2020, 12:34:17 PM »
Quote
Drones can't carry much weight at all, and the constant corrections and drifting would overwhelm any subtle forces from the earths rotation.

I mentioned a modified version so it can be a simple plumb bob with a long wire either stationary or swinging at the dome of the Pantheon, Paris, or ideally at north pole.
addendum:
Using Foucault's concept, we don't need any pendulum in case of using a drone because the four or multiple sides/ faces of the drone are enough for the evidence of earth's rotation if it hovers at one fixed point for a couple of hours.

Except the drone uses active sensors to keep itself positioned.  Cameras, gyros, GPS.  That's going to overwhelm any small rotation you might detect over 40 minutes.  If it was turning due to the Earths motion, it would simply correct itself and turn with it.

Re: Question about the Foucault's Pendulum?
« Reply #10 on: June 12, 2020, 01:30:23 PM »
Quote
Except the drone uses active sensors to keep itself positioned.  Cameras, gyros, GPS.  That's going to overwhelm any small rotation you might detect over 40 minutes.  If it was turning due to the Earths motion, it would simply correct itself and turn with it.

I meant if the drone is under the influence of noncontact gravity force only just like a bob in the case of Foucault's pendulum experiment.

The bob of Foucault's pendulum (either stationary or swinging) is constantly under the influence of the non-contact gravity force of the earth. No idea how does the said bob if swinging transfers its weight "mg" during the rotation of the earth due to such noncontact gravitational force on the surface of the earth if it shows the evidence of earth's rotation.
« Last Edit: June 12, 2020, 01:32:59 PM by E E K »

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rabinoz

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Re: Question about the Foucault's Pendulum?
« Reply #11 on: June 12, 2020, 02:02:54 PM »
How about the idea of using a drone instead of suspending the Foucault's Pendulum from the dome which is in question!

Would we be able to get the same result for the evidence of earth’s rotation if suspend a modified version of Foucault's Pendulum from the bottom of drone which can hover for a couple of hours at one fixed point in a closed environment?
Not at all.
Drones fly in the air and either they are controlled by GPS or will simply move with the air and wherever their propellers direct them.

Quote from: E E K
Source: internet: "Given that your average drone can hover for around half an hour, the four hours, 40 minute record claimed by Spanish drone manufacturer Quaternium is pretty darn impressive"

Re: Question about the Foucault's Pendulum?
« Reply #12 on: June 13, 2020, 12:14:25 AM »
Quote
Not at all.
Drones fly in the air and either they are controlled by GPS or will simply move with the air and wherever their propellers direct them.
- Similar control happens in Foucault's pendulum as well. This means

You didn't comment on the weight transfer of the wire and bob = mg (combined) of Foucault's pendulum which is controlled by the NONCONTACT GRAVITY FORCE OF EARTH from blue traced to the green traced.

"The bob of Foucault's pendulum (either stationary or swinging) is constantly under the influence of the non-contact gravity force of the earth. No idea how does the said bob if swinging transfers its weight "mg" during the rotation of the earth due to such noncontact gravitational force on the surface of the earth if it shows the evidence of earth's rotation".
« Last Edit: June 13, 2020, 01:10:59 AM by E E K »

Re: Question about the Foucault's Pendulum?
« Reply #13 on: June 13, 2020, 03:47:16 AM »
Quote
But the initial swing of the pendulum defines an initial direction and if the top support has low enough friction the plane of the pendulum's swing will remain unchanged.

Sorry but the initial to and fro motion of the pendulum has nothing to do with changing the facing direction of point "A" marked on the outer diameter (big enough) of the wire  – quite clear in words and in animation. Unless I'm conceiving it wrong.

Point A on the outer surface of the wire always faces in the same direction whether the pendulum is at rest or swinging.

Imagine you suspend something on a wire with completely frictionless bearing at the North Pole.  It’s completely free to rotate (or stay still while the earth rotates).

How do set a zero reference to measure the earth’s rotation against?  It might be motionless wrt the earth, or you might have given it a slight spin while setting it up (which could be at any speed).  You could get any result out of it.  You need a way to know that rotation you measure isn’t just some initial rotation you’ve given it.

You can’t align it to anything on earth, because then you’ll measure no rotation.  You could align it to a point in space like a star, but that kind of defeats the whole point of the experiment and it’s easier just to look at the stars.

Swinging the pendulum is what gives you that reference.  Because you’d need to apply another force to change the direction of its momentum.

Re: Question about the Foucault's Pendulum?
« Reply #14 on: June 13, 2020, 05:48:36 AM »
As you said "You can’t align it to anything on earth" Therefore, the question is

How do you separate (de-align) that to and fro swing of the pendulum from the rotation of the earth.

Can you show me the point at which that to and fro swing motionless (remain still) w.r.t rotation of the earth.

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rabinoz

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Re: Question about the Foucault's Pendulum?
« Reply #15 on: June 13, 2020, 05:52:06 AM »
As you said "You can’t align it to anything on earth" Therefore, the question is

How do you separate (de-align) that to and fro swing of the pendulum from the rotation of the earth.

Can you show me the point at which that to and fro swing motionless (remain still) w.r.t rotation of the earth.
From the first swing.

Re: Question about the Foucault's Pendulum?
« Reply #16 on: June 13, 2020, 06:02:42 AM »
As you said "You can’t align it to anything on earth" Therefore, the question is

How do you separate (de-align) that to and fro swing of the pendulum from the rotation of the earth.

Can you show me the point at which that to and fro swing motionless (remain still) w.r.t rotation of the earth.
From the first swing.
- in simple words

I mean the gravitational field of the earth shouldn't have any effect on the pendulum (bob and wire) at all if it is stationary w,r.t to the rotation of the earth. Hope this help 

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rabinoz

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Re: Question about the Foucault's Pendulum?
« Reply #17 on: June 13, 2020, 07:06:09 PM »
As you said "You can’t align it to anything on earth" Therefore, the question is

How do you separate (de-align) that to and fro swing of the pendulum from the rotation of the earth.

Can you show me the point at which that to and fro swing motionless (remain still) w.r.t rotation of the earth.
From the first swing.
- in simple words

I mean the gravitational field of the earth shouldn't have any effect on the pendulum (bob and wire) at all if it is stationary w,r.t to the rotation of the earth. Hope this help
No it doesn't help. Just what do you mean?
The only place the Earth's gravity comes into it is in providing the restoring force to make the pendulum swing
A spring pulling down could provide that.

An ideal large gyroscope could also demonstrate the rotation and, in fact does, in the old mechanical versions of a marine gyrocompass or a gyro-theodolite.

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sceptimatic

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Re: Question about the Foucault's Pendulum?
« Reply #18 on: June 14, 2020, 01:24:45 AM »
Why does the pendulum have to swing in the first place?

Surely the same pendulum just hanging above the table, floor should see the table/floor move around it.

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rabinoz

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Re: Question about the Foucault's Pendulum?
« Reply #19 on: June 14, 2020, 02:31:31 AM »
Why does the pendulum have to swing in the first place?

Surely the same pendulum just hanging above the table, floor should see the table/floor move around it.
Why? How would you know when the pendulum is fixed in space?

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JJA

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Re: Question about the Foucault's Pendulum?
« Reply #20 on: June 14, 2020, 03:36:22 AM »
Why does the pendulum have to swing in the first place?

Surely the same pendulum just hanging above the table, floor should see the table/floor move around it.

This is easy to understand.

Imagine taking one of those huge pendulums and putting it on a giant turntable.  Now, slowly turn it, taking an entire day to do so.  What will happen? Will the weight at the bottom move with the table?  Of course it will.

It's the exact same process as if you took that pendulum and twisted it 360 degrees and then let go. It wouldn't just stay there, it would turn back to it's starting position. It's not on a fishing line, it's heavy metal cable, and that's not going to twist without a force applied.

Now if that weight were suspended in a vacuum on a friction-less bearing, then it would turn.  But that cable is not going to twist with the force of a slow, 24 hour rotation. 

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sceptimatic

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Re: Question about the Foucault's Pendulum?
« Reply #21 on: June 14, 2020, 05:49:14 AM »
Why does the pendulum have to swing in the first place?

Surely the same pendulum just hanging above the table, floor should see the table/floor move around it.
Why? How would you know when the pendulum is fixed in space?
Have the pendulum affixed to the ceiling with no rotary movement and have the table on a fine bearing.
Mark the pendulum ball weight or attach a laser light to it to point down to the table.

Re: Question about the Foucault's Pendulum?
« Reply #22 on: June 14, 2020, 09:36:42 AM »
Why does the pendulum have to swing in the first place?

Surely the same pendulum just hanging above the table, floor should see the table/floor move around it.
Why? How would you know when the pendulum is fixed in space?
Have the pendulum affixed to the ceiling with no rotary movement and have the table on a fine bearing.
Mark the pendulum ball weight or attach a laser light to it to point down to the table.

No rotary movement relative to what?  The room? 

You’ll read zero rotation, just because you set it up to have zero rotation.  It doesn’t tell you anything.

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sceptimatic

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Re: Question about the Foucault's Pendulum?
« Reply #23 on: June 14, 2020, 10:01:10 AM »
Why does the pendulum have to swing in the first place?

Surely the same pendulum just hanging above the table, floor should see the table/floor move around it.
Why? How would you know when the pendulum is fixed in space?
Have the pendulum affixed to the ceiling with no rotary movement and have the table on a fine bearing.
Mark the pendulum ball weight or attach a laser light to it to point down to the table.

No rotary movement relative to what?  The room? 

You’ll read zero rotation, just because you set it up to have zero rotation.  It doesn’t tell you anything.
I set up the table to account for rotation.
If the room moves the ball moves and the table resists movement, meaning the ball should show a change as that building supposedly rotates with the supposed globe.


Re: Question about the Foucault's Pendulum?
« Reply #24 on: June 14, 2020, 10:29:09 AM »
I set up the table to account for rotation.
If the room moves the ball moves and the table resists movement, meaning the ball should show a change as that building supposedly rotates with the supposed globe.

Then you’ve set up the table with some amount of rotation relative to the room, which could be anything.

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sceptimatic

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Re: Question about the Foucault's Pendulum?
« Reply #25 on: June 14, 2020, 10:45:29 AM »
I set up the table to account for rotation.
If the room moves the ball moves and the table resists movement, meaning the ball should show a change as that building supposedly rotates with the supposed globe.

Then you’ve set up the table with some amount of rotation relative to the room, which could be anything.
All I've done is nullified the swing on the pendulum and also nullified the bearing the pendulum is swinging under.
I've instead transferred the bearing to the table so the table can resist the supposed motion of the supposed turning building,

A laser pointer on the ball and aimed at the table should show whether the pendulum rotates and the table stays still.

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JJA

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Re: Question about the Foucault's Pendulum?
« Reply #26 on: June 14, 2020, 10:51:09 AM »
I set up the table to account for rotation.
If the room moves the ball moves and the table resists movement, meaning the ball should show a change as that building supposedly rotates with the supposed globe.

Then you’ve set up the table with some amount of rotation relative to the room, which could be anything.
All I've done is nullified the swing on the pendulum and also nullified the bearing the pendulum is swinging under.
I've instead transferred the bearing to the table so the table can resist the supposed motion of the supposed turning building,

A laser pointer on the ball and aimed at the table should show whether the pendulum rotates and the table stays still.

Nothing is going to move unless the force can overcome friction and torsion.  One rotation every hour is so slow you need a frictionless mount for your weight or it will just move with whatever is spinning, be it the Earth or a big turntable. Even air will provide some resistance and likely you need a vacuum chamber too.

Re: Question about the Foucault's Pendulum?
« Reply #27 on: June 14, 2020, 11:17:48 AM »

All I've done is nullified the swing on the pendulum and also nullified the bearing the pendulum is swinging under.
I've instead transferred the bearing to the table so the table can resist the supposed motion of the supposed turning building,

A laser pointer on the ball and aimed at the table should show whether the pendulum rotates and the table stays still.

Except the table doesn’t resist anything.  You’ve put it on a bearing to spin freely or not at all.  You have no way to know if the table is spinning or not in absolute terms.  It has as much rotation  as you give it when setting it up.

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sceptimatic

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Re: Question about the Foucault's Pendulum?
« Reply #28 on: June 14, 2020, 11:09:43 PM »
Why swing a pendulum at all. It stinks of pretence.


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rabinoz

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Re: Question about the Foucault's Pendulum?
« Reply #29 on: June 14, 2020, 11:46:03 PM »
Why swing a pendulum at all. It stinks of pretence.
It doesn't.