Swinging weight or Hanging weight - proves the earth rotates

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Rayzor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #90 on: July 26, 2016, 03:45:57 AM »
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.

You got it.   

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #91 on: July 26, 2016, 05:09:22 AM »
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.

You got it.

Another example to illustrate Rayzors point, let's say you set up the hammer and string with a bearing like Yendor did at the north pole. The Earth would be rotating around its axis once per day and the hammer would too since both of their axes (had to look up plural of axis) are aligned. Lifting the hammer up by a string you would expect it to continue spinning at the same rate as the Earth.

Same with the Earth and a turn table. Place the hammer on a turn table rotating at 30 rpm, lift the hammer up by a string from the turn table and the hammer should continue to spin at 30 rpm along with the turn table, at least until the friction of the bearing or the string twisting causes it to slow down. Keep in mind that in the turn table example the bearing and mounting location are not spinning along with the turn table where on the Earth they are.

This is why you need an outside momentum imparted on the hammer.

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Ski

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #92 on: July 26, 2016, 09:45:56 AM »
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.

This is both coherent and what I was missing.  Good work!
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AdamSK

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #93 on: July 26, 2016, 11:44:05 AM »
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 is doing both.  If it were not spinning as well as rotating, then it would not continue to face the same direction relative to the rest of the Earth as the Earth spins.

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It can also travel in a straight line and still conserve the angular momentum as measured from that outside point.
Yes, but it needs to continue spinning to do so.  Consider this thought experiment: rotate a dumbbell (two weights separated by a rigid rod) by tying a line to one end so the two ends are not the same distance from the center.  Note that the two ends are not travelling at the same linear velocity, and each time the dumbbell orbits you the outer end has also spun all the way around the inner end.  If you let the dumbbell go, to preserve the total angular momentum but also the distance between the two ends, the dumbbell will have to continue to spin even as it now moves in a straight line.

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Yendor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #94 on: July 26, 2016, 12:02:20 PM »
So, the consensuses is, hanging a heavy object from the ceiling is not going to show earth's movement and for now the only way to prove my goal is to use a swinging ball. I believe like rabinoz that a Foucault's pendulum is not an easy thing to build and If I don't build it like the real thing, no on will trust the results. That is the reason I avoided building any kind of swing object in the first place, I simple don't have the means to build such a device. I need to go back to the drawing board and try to think of another way. Any suggestions, within reason, would be appreciated.
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AdamSK

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #95 on: July 26, 2016, 01:04:53 PM »
So, the consensuses is, hanging a heavy object from the ceiling is not going to show earth's movement and for now the only way to prove my goal is to use a swinging ball. I believe like rabinoz that a Foucault's pendulum is not an easy thing to build and If I don't build it like the real thing, no on will trust the results. That is the reason I avoided building any kind of swing object in the first place, I simple don't have the means to build such a device. I need to go back to the drawing board and try to think of another way. Any suggestions, within reason, would be appreciated.

Why won't a bowling ball hung from a piano wire work?

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Yendor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #96 on: July 26, 2016, 01:32:47 PM »
So, the consensuses is, hanging a heavy object from the ceiling is not going to show earth's movement and for now the only way to prove my goal is to use a swinging ball. I believe like rabinoz that a Foucault's pendulum is not an easy thing to build and If I don't build it like the real thing, no on will trust the results. That is the reason I avoided building any kind of swing object in the first place, I simple don't have the means to build such a device. I need to go back to the drawing board and try to think of another way. Any suggestions, within reason, would be appreciated.

Why won't a bowling ball hung from a piano wire work?

The problem with anything you hang has to keep moving. That involves a electromagnet kicking it along. It also has to be timed to kick. If you don't do that, it won't stay swinging. It will stop before you can get good results.
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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #97 on: July 26, 2016, 02:15:46 PM »
The longer the string, the longer it will keep swinging. If you can keep it swinging for just an hour, I think you could measure goo enough results to calculate roughly the speed to earth is turning (using the formula for lattitude of course)
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Yendor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #98 on: July 26, 2016, 02:22:23 PM »
The longer the string, the longer it will keep swinging. If you can keep it swinging for just an hour, I think you could measure goo enough results to calculate roughly the speed to earth is turning (using the formula for lattitude of course)

I don't have much height, 13 ft. maybe.
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Ski

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #99 on: July 26, 2016, 02:28:11 PM »
You are much taller than I assumed, Yendor.
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Yendor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #100 on: July 26, 2016, 04:17:43 PM »
You are much taller than I assumed, Yendor.

Us yanks eat a lot of corn, makes us tall.
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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #101 on: July 26, 2016, 04:32:42 PM »
13 feet might be enough. that is about a 14 second period, which might run long enough for you to get some measurements done. Just make sure you have a weight that won't be affected by air so much. A heavy sphere would be the best.
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Rayzor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #102 on: July 26, 2016, 05:11:23 PM »
13 feet might be enough. that is about a 14 second period, which might run long enough for you to get some measurements done. Just make sure you have a weight that won't be affected by air so much. A heavy sphere would be the best.

That seems too long for the period of  a 13 ft pendulum,   I calculate the period should be about 4 seconds.    I don't think that 13 ft is high enough.

To get a enough movement to measure without having to restart it,  you probably it need to  run for at least an hour.
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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #103 on: July 26, 2016, 06:14:22 PM »
yeah, I forgot to convert to meters I think.

I don't know if 4 seconds is enough, but if it is the best you have, then I guess it will have to do.
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Rayzor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #104 on: July 27, 2016, 12:56:36 AM »
yeah, I forgot to convert to meters I think.

I don't know if 4 seconds is enough, but if it is the best you have, then I guess it will have to do.

Serendipitous mistake I  think,   13 meters would be a good length,   and  that works out to 42' or so for our metrically challenged  'merican friends.

The real question however is what is the minimum length for a foucault pendulum that will give reasonably accurate results.   The answer is probably somewhere between 10 ft and 50 ft.

So,  I'd suggest Rodney gives his 13 ft version a trial run and see how long it will swing unaided without periodic kicking.   

Then given his latitude we can work out how many degrees the arc should have rotated in that time to decide if it's a measurable amount.

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AdamSK

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #105 on: July 27, 2016, 04:24:10 AM »
Why won't a bowling ball hung from a piano wire work?
The problem with anything you hang has to keep moving. That involves a electromagnet kicking it along. It also has to be timed to kick. If you don't do that, it won't stay swinging. It will stop before you can get good results.
I'd think about a two-story piano wire (10 to 15 feet) would be enough for it to continue swinging quite a while.

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Yendor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #106 on: July 27, 2016, 11:42:38 AM »
The longer the string, the longer it will keep swinging. If you can keep it swinging for just an hour, I think you could measure goo enough results to calculate roughly the speed to earth is turning (using the formula for lattitude of course)

Question,
If a Foucault's pendulum is in a room at certain latitude other then at the poles, shouldn't the room rotate at the speed the earth rotates at that latitude?
"During times of universal deceit, telling the truth becomes a revolutionary act."
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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #107 on: July 27, 2016, 11:54:09 AM »
Well, the farther away from the poles you go, the pendulum is at an angle to the actual rotation of the earth, so the pendulum swings less than a full rotation. The formula is on wikipedia.
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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #108 on: July 27, 2016, 01:37:50 PM »
The longer the string, the longer it will keep swinging. If you can keep it swinging for just an hour, I think you could measure goo enough results to calculate roughly the speed to earth is turning (using the formula for lattitude of course)

Question,
If a Foucault's pendulum is in a room at certain latitude other then at the poles, shouldn't the room rotate at the speed the earth rotates at that latitude?

The earth rotates at the same speed at all latitudes, once every ~24 hours. However, as origamiscienceguy says, as you move away from the poles the vertical axis of the pendulum moves away from the axis of rotation of the earth so that the pendulum precesses more slowly. At the equator the pendulum doesn't precess at all.

The formula is ω = λ sin θ, where ω is the angular precession of the pendulum, λ is the earth's angular velocity and θ is the latitude. It's a simple formula but my googling suggests that the mathematics behind it is less straightforward.

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Yendor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #109 on: July 27, 2016, 02:08:09 PM »
I've thought of another idea. Take a simple compass, the needle always points north no matter what the compass housing does. You can rotate it around all you want and the needle will still go back pointing north. You could say it locks in pointing to the north. The housing, on the other hand, that supports the needle is physically on the earth and it will rotate along with the earth and the needle will always stay locked in pointing north. I would think that, if the earth does rotate, the housing will rotate too and the needle will still point north.

In my opinion, this is a better test then the hanging hammer because there is no bearing to add friction, wind or air has no effect on it because it is in a sealed housing and the needle can not rotate with the earth because it always goes back pointing north.

I've done this with my compass. I set a reference point on the housing and lined the needle up to it. The compass has been setting on my desk for over 30 minutes and the needle is still pointing at the reference point. it has not moved at all.

Do you think this is a legitimate test and does it prove anything?
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sokarul

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #110 on: July 27, 2016, 02:18:25 PM »
You are so confused it's unbelievable.
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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #111 on: July 27, 2016, 02:21:57 PM »
I've thought of another idea. Take a simple compass, the needle always points north no matter what the compass housing does. You can rotate it around all you want and the needle will still go back pointing north. You could say it locks in pointing to the north. The housing, on the other hand, that supports the needle is physically on the earth and it will rotate along with the earth and the needle will always stay locked in pointing north. I would think that, if the earth does rotate, the housing will rotate too and the needle will still point north.

In my opinion, this is a better test then the hanging hammer because there is no bearing to add friction, wind or air has no effect on it because it is in a sealed housing and the needle can not rotate with the earth because it always goes back pointing north.

I've done this with my compass. I set a reference point on the housing and lined the needle up to it. The compass has been setting on my desk for over 30 minutes and the needle is still pointing at the reference point. it has not moved at all.

Do you think this is a legitimate test and does it prove anything?

Would you expect that the rotation of the earth would make either magnetic north or true north change direction from where you are, relative to the earth?

If not, it doesn't test anything.

Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #112 on: July 27, 2016, 02:32:26 PM »
I've thought of another idea. Take a simple compass, the needle always points north no matter what the compass housing does. You can rotate it around all you want and the needle will still go back pointing north. You could say it locks in pointing to the north. The housing, on the other hand, that supports the needle is physically on the earth and it will rotate along with the earth and the needle will always stay locked in pointing north. I would think that, if the earth does rotate, the housing will rotate too and the needle will still point north.

In my opinion, this is a better test then the hanging hammer because there is no bearing to add friction, wind or air has no effect on it because it is in a sealed housing and the needle can not rotate with the earth because it always goes back pointing north.

I've done this with my compass. I set a reference point on the housing and lined the needle up to it. The compass has been setting on my desk for over 30 minutes and the needle is still pointing at the reference point. it has not moved at all.

Do you think this is a legitimate test and does it prove anything?
Won't work at all. Your house is not spinning independently of the earth. One side of your house always points north.
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Yendor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #113 on: July 27, 2016, 03:06:46 PM »
I guess I am confused. Is the room not rotating where the pendulum is located and the pendulum swing in the same direction as the room rotates under it. If it doesn't do that, what does it do?
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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #114 on: July 27, 2016, 03:21:47 PM »
That is correct, your house and the whole earth rotate underneath it. However, your compass will always face the same direction because your house always faces the same direction.
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Yendor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #115 on: July 27, 2016, 03:38:42 PM »
That is correct, your house and the whole earth rotate underneath it. However, your compass will always face the same direction because your house always faces the same direction.

look at this animation, the pendulum, which is the needle in this case, always faces the same direction and follows the same plane. The rotating frame is the earth, which is the compass housing in this case.



Animation of a Foucault pendulum at the Pantheon in Paris (48°52' North), with the Earth's rotation rate greatly exaggerated. The green trace shows the path of the pendulum bob over the ground (a rotating reference frame), while in any vertical plane. The actual plane of swing appears to rotate only, relative to the Earth rotating.




"During times of universal deceit, telling the truth becomes a revolutionary act."
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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #116 on: July 27, 2016, 03:39:51 PM »
That is correct, although the end of the pendulum will "twist" with the earth (as seen by your power cable experiment)
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Yendor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #117 on: July 27, 2016, 03:42:21 PM »
That is correct, although the end of the pendulum will "twist" with the earth (as seen by your power cable experiment)

I know it twists, but that's just the result of a swinging object. It still swings in the same plane and the earth rotates under it, or they say.
"During times of universal deceit, telling the truth becomes a revolutionary act."
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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #118 on: July 27, 2016, 03:44:15 PM »
I think you get it.

Have you tried to build one yet?
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Yendor

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Re: Swinging weight or Hanging weight - proves the earth rotates
« Reply #119 on: July 27, 2016, 03:46:47 PM »
I think you get it.

Have you tried to build one yet?

You think I got it, it's a compass. There is no building to it.
"During times of universal deceit, telling the truth becomes a revolutionary act."
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