Swinging weight or Hanging weight - proves the earth rotates

Of course you're right. The movement of the air is only a hindrance to the Foucault Pendulum's operation.

Not in the manner you are thinking, if I understand you correctly.

But, if the rotation is due to the rotation of the celestial objects, why is the rotation at the South Pole still around 15°/hr, but in the opposite direction to that at the North-Pole - though I doubt it has actually been tested at the North Pole, but is certainly has at the South Pole as in my post a little earlier Re: Swinging weight or Hanging weight - proves the earth rotates « Reply #51 on: Today at 08:27:38 PM ».

Because the celestial parade is the source of your non-inertial frame. Facing the south the stars parade left to right. In the north facing the center of the rotating frame the stars parade right to left.  On the equator, the fictious forces due to the relationship between the rotating frames cancel each other out.

Quote from: Ski on July 24, 2016, 11:41:39 PM

Quote from: Rayzor on July 24, 2016, 10:54:49 PM

I said it already in the other thread but it obviously needs to be repeated here.

It's all about Inertia.   Simple you might think,  but the implications run deep.   An object resists being accelerated,  once it's moving it wants to keep moving,  once it stops it wants to stay stopped.

Correct. Which is why the free hanging weight would stay stationary in its own FoR while the room  would appear to continue to rotate.
Or alternatively the observer would see the free hanging weight rotate due the fictious force in his non-inertial frame.

No I disagree,  It's already rotating along with the room and everything else,  what's going to STOP it from just continuing to rotate along with the room?

I'm not sure if you're serious 

A rotating object is constantly changing direction. If you have a ball on a string and whip it around your head,  when you let it go it flies in a straight line with no rotation because no force is acting on it. What force is being applied to the hammer? The air is not imparting enough momentum (or show me the math), and the weight is free hanging, so the rotating spaceship/room/earth/etc is not acting on it. It stays the same in its inertial frame while the room moves (or again, in the non-inertial rotating frame of the observer, a fictitious force acts on the ball making it appear to rotate).

Quote from: Rayzor on July 24, 2016, 11:51:49 PM

Quote from: Ski on July 24, 2016, 11:41:39 PM

Quote from: Rayzor on July 24, 2016, 10:54:49 PM

I said it already in the other thread but it obviously needs to be repeated here.

It's all about Inertia.   Simple you might think,  but the implications run deep.   An object resists being accelerated,  once it's moving it wants to keep moving,  once it stops it wants to stay stopped.

Correct. Which is why the free hanging weight would stay stationary in its own FoR while the room  would appear to continue to rotate.
Or alternatively the observer would see the free hanging weight rotate due the fictious force in his non-inertial frame.

No I disagree,  It's already rotating along with the room and everything else,  what's going to STOP it from just continuing to rotate along with the room?

I'm not sure if you're serious 

A rotating object is constantly changing direction. If you have a ball on a string and whip it around your head,  when you let it go it flies in a straight line with no rotation because no force is acting on it. What force is being applied to the hammer? The air is not imparting enough momentum (or show me the math), and the weight is free hanging, so the rotating spaceship/room/earth/etc is not acting on it. It stays the same in its inertial frame while the room moves (or again, in the non-inertial rotating frame of the observer, a fictitious force acts on the ball making it appear to rotate).

I'm serious.  The hammer has inertia,  It's already moving right along with the room and everything else in it.  What force is going to change that? 

If the hammer were  a few tens of kms across,  you might see some rotation relative to the earth due to one side moving slower due to being closer to one of the poles of rotation.  Like weather patterns.

I'm serious.  The hammer has inertia,  It's already moving right along with the room and everything else in it.  What force is going to change that? 

A fictitious one!
The room is a rotating frame, silly globularist. A free hanging hammer within that frame experiences fictious force.

Or again, from the inertial frame of the hammer, the hammer stays still while the room continues to rotate about.

Quote from: Rayzor

I'm serious.  The hammer has inertia,  It's already moving right along with the room and everything else in it.  What force is going to change that? 

A fictitious one!
The room is a rotating frame, silly globularist. A free hanging hammer within that frame experiences fictious force.

Or again, from the inertial frame of the hammer, the hammer stays still while the room continues to rotate about.

Ok,  let me try to put it another way, 

Imagine we have a  large mass ( say a cross pein hammer) suported by a frictionless bearing and we place this on a lazy susan and start the lazy susan rotating, ,  the mass will remain stationary and appear to be rotating with respect to the lazy susan's  FoR, 

Now let's change the initial conditions,  when we start the lazy susan we also start the mass rotating at exactly the same angular velocity,  now the mass is stationary with respect to the lazy susan's FoR.

The "fictitous" forces  ( centrifugal and coriolus ) experienced by being in the rotating frame are experienced by all the objects in the room,  therefore zero relative motion.  Start the hammer swinging  and everything changes,  the hammer now has angular momentum independant of the room, and you will see rotation.

If it is free hanging,  it is in its own inertial frame and there is no force acting on it. Hence no movement of the globe/hammer within that frame. The room meanwhile is still being acted upon by the earth.


From the noninertial rotating frame of the room, the room is stationary and the observer, chair, whathaveyou are motionless within that frame because they are being acted upon by the room/floor. The hammer/floating globe is not being acted upon by the floor/room, so it appears to be moving relative the room, but it is only a fictious one because that frame is non-inertial.

If it is free hanging,  it is in its own inertial frame and there is no force acting on it. Hence no movement of the globe/hammer within that frame. The room meanwhile is still being acted upon by the earth.


From the noninertial rotating frame of the room, the room is stationary and the observer, chair, whathaveyou are motionless within that frame because they are being acted upon by the room/floor. The hammer/floating globe is not being acted upon by the floor/room, so it appears to be moving relative the room, but it is only a fictious one because that frame is non-inertial.

You are correct as far as it goes,  but you are ignoring the initial conditions, and  that is that the hammer was already rotating with the room before it was suspended.   It just continues to rotate along with the room and everything else in it.

Give it some angular momentum independent of the room and you'll see a different result.

Nothing is acting on the hammer. No force is being applied to it once it is released.  The vector of your motion is constantly changing while you are in the rotating FoR. What would make the hammer change direction if it is free hanging?

You are on a merry- go-round in space. Holding a hammer/globe. The merry-go-round applies angular momentum to you while it spins at R rpm. You apply the same to the hammer.  If you release the hammer/globe, it does not continue to circle around with you or present its same face to you while you sit on the merry-go-round because you are still changing directions and nothing is acting on the hammer/globe. From your rotating FoR something appears to be acting on the hammer/globe, but it is not. The hammer/globe is at rest in it's own FoR because the merry-go-round (via Rayzor) is no longer acting on it.

Nothing is acting on the hammer. No force is being applied to it once it is released.  The vector of your motion is constantly changing while you are in the rotating FoR. What would make the hammer change direction if it is free hanging?

Correct,  so if it was rotating along with the room when it was released,  what would it do,  continue to rotate or not?

You are on a merry- go-round in space. Holding a hammer/globe. The merry-go-round applies angular momentum to you while it spins at R rpm. You apply the same to the hammer.  If you release the hammer/globe, it does not continue to circle around with you or present its same face to you while you sit on the merry-go-round because you are still changing directions and nothing is acting on the hammer/globe. From your rotating FoR something appears to be acting on the hammer/globe, but it is not. The hammer/globe is at rest in it's own FoR because the merry-go-round (via Rayzor) is no longer acting on it.

I got a bit lost with this,  the forces acting on the hammer/globe  are dependent on the axis of rotation and the relative velocities both before and after it's released.   The hammer/globe is in an inertial frame, while  I remain in  the rotating non inertial frame.  But the initial angular momentum and velocity of the hammer remain unchanged.   

Maybe you can clarify,   are you saying that the instant that Rodney releases the hammer, it starts moving at 1000 mph towards the West?  ( or is it East? )

Quote from: rabinoz

Of course you're right. The movement of the air is only a hindrance to the Foucault Pendulum's operation.

Not in the manner you are thinking, if I understand you correctly.

Quote

But, if the rotation is due to the rotation of the celestial objects, why is the rotation at the South Pole still around 15°/hr, but in the opposite direction to that at the North-Pole - though I doubt it has actually been tested at the North Pole, but is certainly has at the South Pole as in my post a little earlier Re: Swinging weight or Hanging weight - proves the earth rotates « Reply #51 on: Today at 08:27:38 PM ».

Because the celestial parade is the source of your non-inertial frame. Facing the south the stars parade left to right. In the north facing the center of the rotating frame the stars parade right to left.  On the equator, the fictious forces due to the relationship between the rotating frames cancel each other out.

On your fictitious flat earth the "celestial parade" all rotates clockwise looking down on the North Pole, so why is there any particular signifance in the equator.

Now back on the real earth.
The Foucault pendulum I referred to in South Pole Foucault Pendulum, Winter, 2001 was at the Geographical South Pole (or within a short distance of it), so how can anyone face south from there?

Quote from: AdamSK on July 24, 2016, 02:44:58 PM

Did you test your bearing to determine the minimum torque necessary to move it?

I was getting such negative response because of the bearing, I decide to think of something else. That is why I came up with the levitating earth idea, It has no friction and it is isolated from the base with air. So, if the base is on the earth and the globe was suspended above then as the earth rotated the globe should stay in place. I felt that would be okay. What are your thoughts?

I would be concerned that something so light would rotate quite a bit just from small movements of air, but otherwise it seems sound.

Again, a couple of experiments would be a good idea to see how it would operate.  Slowly and carefully turn the base to make sure the globe doesn't turn with it.  Also do something to make sure the globe doesn't stay aligned to the Earth's magnetic field, which light magnetic objects tend to do.

The pendulum doesn't need a rotating anchor. The bob at the end of the pendulum will rotate with the earth, but the direction that the pendulum swings will not change.

Quote from: Yendor on July 24, 2016, 02:52:12 PM

Quote from: AdamSK on July 24, 2016, 02:44:58 PM

Did you test your bearing to determine the minimum torque necessary to move it?

I was getting such negative response because of the bearing, I decide to think of something else. That is why I came up with the levitating earth idea, It has no friction and it is isolated from the base with air. So, if the base is on the earth and the globe was suspended above then as the earth rotated the globe should stay in place. I felt that would be okay. What are your thoughts?

I would be concerned that something so light would rotate quite a bit just from small movements of air, but otherwise it seems sound.

Again, a couple of experiments would be a good idea to see how it would operate.  Slowly and carefully turn the base to make sure the globe doesn't turn with it.  Also do something to make sure the globe doesn't stay aligned to the Earth's magnetic field, which light magnetic objects tend to do.

I've messed with one of those levitating globes before.  I blew on one side to get it spinning, but after a little while it eventually slowed and stopped due to the surface friction with the air around it.

The other problem is the same with the hammer that was brought up (I hadn't even thought about it earlier), it's already rotating when it's set up, and would first require a force to stop it from rotating.  The little levitating globe is so light, even if you rotated the opposite way and let it stop on it's own, it would probably just start rotating the other way with the room, etc, eventually just from the surface friction with the air. 

Here's a paper describing how to make an accurate desktop sized foucault pendulum.    Looks somewhat doable,   I'd probably chuck the 555 timers and put in a micro,   but  that's not the point.  The technique for making it accurate is clever.

http://arxiv.org/pdf/0902.1829v2.pdf

Here's a paper describing how to make an accurate desktop sized foucault pendulum.    Looks somewhat doable,   I'd probably chuck the 555 timers and put in a micro,   but  that's not the point.  The technique for making it accurate is clever.

Isn't this device causing the pendulum to rotate in the opposite direction, such that if the Earth were not rotating this device would still result in seeing the pendulum rotate?

The wire won't twist up, the ball at the end will twist with it. That is why you don't need a rotator. However, the direction that the pendulem swings will not change. That is why you need a pendulem.

think about this some more. Okay, we've or you have determined that the ball does not have a swivel or a rotating device. That means that the ball is hanging from the ceiling by a piano wire. Would you not think that unless there was something to prevent the wire from twisting up, it would in fact twist up because it is directly connected to the ceiling. In other words, because it is hard connected to the part that is suppose to rotate with the earth, the ceiling support, it would rotate along with the earth too. In my mind, the only way to prevent it from doing that is to have some kind of rotating device that would allow the ceiling to rotate, but the wire and ball wouldn't. Unless I'm missing something, I think I'm right? What do you think?

Quote from: origamiscienceguy on July 24, 2016, 04:05:19 PM

The wire won't twist up, the ball at the end will twist with it. That is why you don't need a rotator. However, the direction that the pendulem swings will not change. That is why you need a pendulem.

think about this some more. Okay, we've or you have determined that the ball does not have a swivel or a rotating device. That means that the ball is hanging from the ceiling by a piano wire. Would you not think that unless there was something to prevent the wire from twisting up, it would in fact twist up because it is directly connected to the ceiling. In other words, because it is hard connected to the part that is suppose to rotate with the earth, the ceiling support, it would rotate along with the earth too. In my mind, the only way to prevent it from doing that is to have some kind of rotating device that would allow the ceiling to rotate, but the wire and ball wouldn't. Unless I'm missing something, I think I'm right? What do you think?

That is correct. The bob at the end WILL twist with the planet, but that is not a problem because the DIRECTION THAT THE PENDULEM SWINGS will not twist with the planet.

Please do this to visualize it.

Take a short power chord and hold one end in your hand. Your hand will twist to simulate the earth's roation. Leave the other end hanging. Without swinging it, twist your hand, the end of the cord will tiwst too.

Next, set the end swinging like a pendulum, and twist your hand. You will see that the end will twist, but the pendulum will still swing in the same direction.

Quote from: Yendor on July 25, 2016, 02:40:58 PM

Quote from: origamiscienceguy on July 24, 2016, 04:05:19 PM

The wire won't twist up, the ball at the end will twist with it. That is why you don't need a rotator. However, the direction that the pendulem swings will not change. That is why you need a pendulem.

think about this some more. Okay, we've or you have determined that the ball does not have a swivel or a rotating device. That means that the ball is hanging from the ceiling by a piano wire. Would you not think that unless there was something to prevent the wire from twisting up, it would in fact twist up because it is directly connected to the ceiling. In other words, because it is hard connected to the part that is suppose to rotate with the earth, the ceiling support, it would rotate along with the earth too. In my mind, the only way to prevent it from doing that is to have some kind of rotating device that would allow the ceiling to rotate, but the wire and ball wouldn't. Unless I'm missing something, I think I'm right? What do you think?

That is correct. The bob at the end WILL twist with the planet, but that is not a problem because the DIRECTION THAT THE PENDULEM SWINGS will not twist with the planet.

Please do this to visualize it.

Take a short power chord and hold one end in your hand. Your hand will twist to simulate the earth's roation. Leave the other end hanging. Without swinging it, twist your hand, the end of the cord will tiwst too.

Next, set the end swinging like a pendulum, and twist your hand. You will see that the end will twist, but the pendulum will still swing in the same direction.

Okay, I just tried it and you are right.

That is why the pendulum works, but not the hammer.

Here's a paper describing how to make an accurate desktop sized foucault pendulum.    Looks somewhat doable,   I'd probably chuck the 555 timers and put in a micro,   but  that's not the point.  The technique for making it accurate is clever.

http://arxiv.org/pdf/0902.1829v2.pdf

Won't be accepted in this EZF!

EZF = Equation Free Zone.

Quote from: 29silhouette on July 24, 2016, 10:51:52 AM

Having weights further out would help a little, but you'll still basically need a bearing with 'zero' resistance.  If you turn your hammer slowly, will it continue to slowly spin for a prolonged period of time after letting go?  Perhaps try turning the upper part very slowly and see if the hammer turns with it, or remains stationary.  Remember it's only .0007rpm at the poles, and even slower at other latitudes.

A pendulum swinging back and forth is traveling in a straight line and has momentum.  As the room slowly rotates, there is nothing to force a change in the direction of it's swing.

Here is an animation of how it works.  Embedding isn't working for me for some reason. nevermind
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I got confused watching the video.

Do I dare ask.... what was confusing about it?  If you don't mind telling us.

Correct,  so if it was rotating along with the room when it was released,  what would it do,  continue to rotate or not?

Not. If you play on a merry-go-round with a ball, the ball doesnt continue rotating with you when you release it. It only rotates if your are transferring the momentum (by holding it). Once it is free of outside forces, it continues on it's course from the last outside force. You meanwhile are constantly changing direction because you are still being acted upon by the ride.

got a bit lost with this, 

Noticed

Quote from: Rayzor on July 25, 2016, 02:43:23 AM

Correct,  so if it was rotating along with the room when it was released,  what would it do,  continue to rotate or not?

Not. If you play on a merry-go-round with a ball, the ball doesnt continue rotating with you when you release it. It only rotates if your are transferring the momentum (by holding it). Once it is free of outside forces, it continues on it's course from the last outside force. You meanwhile are constantly changing direction because you are still being acted upon by the ride.

Quote

got a bit lost with this, 

Noticed

Ok,  let's try one last time,  just before you release the object it, you give it a spin,  after release does it keep spinning or does it stop?

I don't think you know what angular momentum is.  The free hanging hammer is not spinning.  It is (charitably assuming RE) rotating about an outside point.  It can also travel in a straight line and still conserve the angular momentum as measured from that outside point.

When I spin a ball on a rope and release it, it travels in a straight line. It leaves tangentially. It does not lose angular momentum from the frame of me (the center of the system) no matter how far away it goes in that straight line because the radius gets bigger. It's math. It does not continue to rotate about me. That's not what angular momentum is.

It's obvious that you don't think I know what I'm talking about,  hence your attempt to educate me, but feel free to have an authority you trust explain it to you. Bonus points if you provide a link to that attempt.

Quote from: Rayzor

I'm serious.  The hammer has inertia,  It's already moving right along with the room and everything else in it.  What force is going to change that? 

A fictitious one!
The room is a rotating frame, silly globularist. A free hanging hammer within that frame experiences fictious force.

Or again, from the inertial frame of the hammer, the hammer stays still while the room continues to rotate about.

Sure, but it would be absolutely impossibly to detect any motion of the hammer, relative to the room, unless you manage to get a massive (tons) "hammer" and a frictionless support.

The idea is only useful as a "thought experiment". And the OP was about the practicality of actually detecting the rotation of the earth.

Mind you in my opinion a Foucault Pendulum is hardly a thing an amateur can easily build.
Foucault's was a 28 kg brass-coated lead bob with a 67 metre long wire!

I don't think you know what angular momentum is.  The free hanging hammer is not spinning.  It is (charitably assuming RE) rotating about an outside point.  It can also travel in a straight line and still conserve the angular momentum as measured from that outside point.

When I spin a ball on a rope and release it, it travels in a straight line. It leaves tangentially. It does not lose angular momentum from the frame of me (the center of the system) no matter how far away it goes in that straight line because the radius gets bigger. It's math. It does not continue to rotate about me. That's not what angular momentum is.

It's obvious that you don't think I know what I'm talking about,  hence your attempt to educate me, but feel free to have an authority you trust explain it to you. Bonus points if you provide a link to that attempt.

No,  I said one last attempt.  You failed to understand the simplest version I can describe.  You make me wonder what other simple concepts you might be failing to grasp.
There's a very good reason it's called "foucault's pendulum"  and not called "foucault's hammer" or "foucault's suspended object".   You figure it out on your own, and let me know what the answer is.

Quote from: Ski on July 25, 2016, 12:26:38 AM

Quote from: Rayzor

I'm serious.  The hammer has inertia,  It's already moving right along with the room and everything else in it.  What force is going to change that? 

A fictitious one!
The room is a rotating frame, silly globularist. A free hanging hammer within that frame experiences fictious force.

Or again, from the inertial frame of the hammer, the hammer stays still while the room continues to rotate about.

Sure, but it would be absolutely impossibly to detect any motion of the hammer, relative to the room, unless you manage to get a massive (tons) "hammer" and a frictionless support.

The idea is only useful as a "thought experiment". And the OP was about the practicality of actually detecting the rotation of the earth.

Mind you in my opinion a Foucault Pendulum is hardly a thing an amateur can easily build.
Foucault's was a 28 kg brass-coated lead bob with a 67 metre long wire!

Nope still won't work no matter how heavy it is or how perfect the bearing.   Unless it get's tens of km across and then you might see a differential because one side is closer to one of the poles.

Quote from: rabinoz on July 26, 2016, 02:00:13 AM

Quote from: Ski on July 25, 2016, 12:26:38 AM

Quote from: Rayzor

I'm serious.  The hammer has inertia,  It's already moving right along with the room and everything else in it.  What force is going to change that? 

A fictitious one!
The room is a rotating frame, silly globularist. A free hanging hammer within that frame experiences fictious force.

Or again, from the inertial frame of the hammer, the hammer stays still while the room continues to rotate about.

Sure, but it would be absolutely impossibly to detect any motion of the hammer, relative to the room, unless you manage to get a massive (tons) "hammer" and a frictionless support.

The idea is only useful as a "thought experiment". And the OP was about the practicality of actually detecting the rotation of the earth.

Mind you in my opinion a Foucault Pendulum is hardly a thing an amateur can easily build.
Foucault's was a 28 kg brass-coated lead bob with a 67 metre long wire!

Nope still won't work no matter how heavy it is or how perfect the bearing.   Unless it get's tens of km across and then you might see a differential because one side is closer to one of the poles.

We might be at cross purposes. By support I meant a sliding support, or floating in a massive tank of mercury.
So I'm not claiming that this massive hammer will rotate (wrt the room), but at anywhere but right at the poles and on the equator it will have try to keep moving, just like to ball on the merry-go-round.

Quote from: Rayzor on July 26, 2016, 02:09:55 AM

Quote from: rabinoz on July 26, 2016, 02:00:13 AM

Quote from: Ski on July 25, 2016, 12:26:38 AM

Quote from: Rayzor

I'm serious.  The hammer has inertia,  It's already moving right along with the room and everything else in it.  What force is going to change that? 

A fictitious one!
The room is a rotating frame, silly globularist. A free hanging hammer within that frame experiences fictious force.

Or again, from the inertial frame of the hammer, the hammer stays still while the room continues to rotate about.

Sure, but it would be absolutely impossibly to detect any motion of the hammer, relative to the room, unless you manage to get a massive (tons) "hammer" and a frictionless support.

The idea is only useful as a "thought experiment". And the OP was about the practicality of actually detecting the rotation of the earth.

Mind you in my opinion a Foucault Pendulum is hardly a thing an amateur can easily build.
Foucault's was a 28 kg brass-coated lead bob with a 67 metre long wire!

Nope still won't work no matter how heavy it is or how perfect the bearing.   Unless it get's tens of km across and then you might see a differential because one side is closer to one of the poles.

We might be at cross purposes. By support I meant a sliding support, or floating in a massive tank of mercury.
So I'm not claiming that this massive hammer will rotate (wrt the room), but at anywhere but right at the poles and on the equator it will have try to keep moving, just like to ball on the merry-go-round.

Correct,  you won't see any rotation of the floating object  from the room's FoR   The components of linear  and angular momentum that are imparted at the point of release are unchanged.

To have a component that will resist any rotation of the room's FoR we need some independently imparted angular momentum,  like you would get with a pendulum, or a gyroscope.   Just sitting still won't work.

When I spin a ball on a rope and release it, it travels in a straight line. It leaves tangentially. It does not lose angular momentum from the frame of me (the center of the system) no matter how far away it goes in that straight line because the radius gets bigger. It's math. It does not continue to rotate about me. That's not what angular momentum is.

I think what Rayzor is alluding to is that in this example with a ball, the ball itself is turning on an axis of its own, relative to an outside reference frame (because it keeps the same face towards you). Then when you let it go it travels in a straight line but also keeps turning on that axis.

(Rayzor, please feel free to correct me if I'm wrong here, I'm not even sure that this is what it would do.)

So in the case of the hammer, before decoupling, it already has a turning motion about its own axis due to the earth's rotation. When decoupled it will continue that turning motion and therefore maintain its orientation with respect to the room.