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Author Topic: Is it possible to make a lift/elevator to get into space?  (Read 13958 times)

Offline Pmb

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #25 on: 15/04/2012 03:48:34 »
I think if everyone called it the centrifugal pseudoforce instead of the centrifugal force, there wouldn't be an issue.
I disagree. The reasons I disagree are found in the Newtonian Mechanics, A.P. French, The M.I.T. Introductory Physics Series, W.W. Norton Pub. , (1971). If you have this text then please turn to page 499 where French writes
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To describe such force as "fictitious" is therefore somewhat misleading. One would like to have some convenient label that distinguishes inertial forces from forces that arise from true physical interactions, and the term "psuedo-force" is often used. Even this, however, does not do justice to such forces experienced by someone who is actually in the accelerating frame of reference. Probably the original, strictly technical name, "inertial force," which is free of any questionable overtones, remains the best description.
So to refer to forces which are not expressed as a 4-force one uses the term Inertial Force. A similar remark can be found in Variational Principles of Mechanics - 4th Ed., Cornelius Lanczos, Dover Pub. On page 98 the author writes.
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Whenever the motion of the reference system generates a force which has to be added to the relative force of inertia I’, measured in that system, we call that force an “apparent force.” The name is well chosen, inasmuch as that force does not exist in the absolute system. The name is misleading, however, if it is interpreted as a force which is not as “real” as any given physical force. In the moving reference system the apparent force is a perfectly real force, which is not distinguishable in its nature from any other impressed force. Let us suppose that the observer is not aware of the fact that his reference system is in accelerated motion. Then purely mechanical observations cannot reveal to him that fact.
I recall that Lanczos also uses the term Einstein force to refer to inertial forces. It's been a very long time since I had similar conversations so I'm less than 100% accurate.

 

Offline Pmb

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #26 on: 15/04/2012 03:49:32 »
I think if everyone called it the centrifugal pseudoforce instead of the centrifugal force, there wouldn't be an issue.
That's like saying that if everybody in the world became a Muslim then we'd have world peace.

Yes, well I am sure the Muslim faith is also the correct faith from certain frames of reference ;)
ROTFL!!
 

Offline Geezer

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #27 on: 15/04/2012 03:53:25 »

It is still quite a real force from certain frames of reference.


Only if you try to have your cake and eat it too.
 
If you use the Earth as your frame of reference, it is not rotating, so there is no centrifugal or centripetal anything. There are only forces.
 
As soon as you admit that the Earth is rotating, unless you want to re-write the most fundamental physics, you have to account for the forces that cause things to follow a curved path, and those are quite clearly centripetal forces.
 
We can use the notion of centrifugal force as a shortcut in calculations, but unfortunately, too many people fall into the trap of thinking that using the term legitimizes faulty science.
 

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #28 on: 15/04/2012 04:01:51 »
If you use the Earth as your frame of reference, it is not rotating, so there is no centrifugal or centripetal anything.
That is incorrect. E.g. the Coriolis force, a velocity dependant force, is found in the corotating frame of the Earth.
 

Offline Phractality

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #29 on: 15/04/2012 04:16:02 »
I can't believe we still don't have flying pigs! There don't seem to be any on Youtube. All it takes is wings a harness and a tow rope behind an airplane.

Yes; it will be possible to build a space elevator within a few decades. But can it be done both safely and economically? At present, there's too much danger of collisions with space junk. We need to pick up our trash. If we allow entrepreneurs to attempt it without adequate safety margins, we'll end up with a permanent CNT ribbon wrapped all the way around the equator. It will be an eyesore, an ecological disaster and a hazard to shipping and aircraft.

And if the whole world converted to Islam, the Shiites and Sunnis would still be bombing each other's mosques. In fact, they'd take all those bombs they've been making for infidels and use them on each other.
 

Offline Geezer

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #30 on: 15/04/2012 04:40:44 »
OK everyone.
 
No more religion if you please.
 
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Offline Geezer

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #31 on: 15/04/2012 04:41:55 »
If you use the Earth as your frame of reference, it is not rotating, so there is no centrifugal or centripetal anything.
That is incorrect. E.g. the Coriolis force, a velocity dependant force, is found in the corotating frame of the Earth.

If the Earth is your frame, there is no rotation, other than all the stuff that's rotating around it. As I said, you can't have your cake and eat it too.
 
The Coriolis force is also a ficticious force. It's a very convenient way of describing effects we see on Earth, but those effects are really just consequences of inertia, gravity, and the Earth's motion. It's still your basic Newtonian physics.
 
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Offline Ćthelwulf

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #32 on: 15/04/2012 10:46:22 »
If you use the Earth as your frame of reference, it is not rotating, so there is no centrifugal or centripetal anything.
That is incorrect. E.g. the Coriolis force, a velocity dependant force, is found in the corotating frame of the Earth.

If the Earth is your frame, there is no rotation, other than all the stuff that's rotating around it. As I said, you can't have your cake and eat it too.
 
The Coriolis force is also a ficticious force. It's a very convenient way of describing effects we see on Earth, but those effects are really just consequences of inertia, gravity, and the Earth's motion. It's still your basic Newtonian physics.
 
Geezer (Not Moderator)

There must be a difference between the centrifugal force and the centripetal. This is the common difference found in books:

The Centripetal force is directed toward the center of rotation of an orbiting body which follows a curved path. Then the Centrifugal force is the apparent force which is equal and opposite to the centripetal force, which moves the  rotating body away from the center of rotation, caused by the inertia of the body.
 

Offline wolfekeeper

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #33 on: 19/04/2012 17:50:43 »
If you use the Earth as your frame of reference, it is not rotating, so there is no centrifugal or centripetal anything.
That is incorrect. E.g. the Coriolis force, a velocity dependant force, is found in the corotating frame of the Earth.

If the Earth is your frame, there is no rotation, other than all the stuff that's rotating around it. As I said, you can't have your cake and eat it too.
 
The Coriolis force is also a ficticious force. It's a very convenient way of describing effects we see on Earth, but those effects are really just consequences of inertia, gravity, and the Earth's motion. It's still your basic Newtonian physics.
 
Geezer (Not Moderator)
Yes, but it's a real force that appears when you transform an inertial frame into a rotating reference frame such as that rotating with the surface of Earth.

When you do that, you get two effects, the Coriolis force which acts when things move around, and the centrifugal force which pushes things away from the axis of rotation even when they don't (relative to the surface of the Earth).

They come out of the same equation.

These are REAL effects that can kill you; just like gravity. They are as real as gravity. Coriolis force is a big effect in weather systems it's exactly as real as centrifugal effect.
 

Offline Geezer

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #34 on: 19/04/2012 23:28:59 »

There must be a difference between the centrifugal force and the centripetal. This is the common difference found in books:

The Centripetal force is directed toward the center of rotation of an orbiting body which follows a curved path. Then the Centrifugal force is the apparent force which is equal and opposite to the centripetal force, which moves the  rotating body away from the center of rotation, caused by the inertia of the body.
 

All forces produce a reaction. The apparent centrifugal force is simply the reaction to the real centripetal force. Why textbooks continue to pander to the notion of centrifugal force is beyond me. It would confuse students a lot less if they just referred to it as centripetal reaction.
 
Magnetism produces forces too, but we don't seem to feel the need to invent special names for those reactions.
 
The reason I am so militant about this is because it dilutes the fundamental physics. Objects with mass tend to move in straight lines unless a force acts to deviate their path from a straight line. "Centrifugal force" implies that objects will suddenly accelerate along a path at 90 degrees to their current motion, which is complete nonsense.
 
I'm not just being "picky"; I'm demanding that people don't make things any more complicated than they really are.
 

Offline wolfekeeper

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #35 on: 19/04/2012 23:32:52 »
No, you can have centrifugal without centripetal. When an object isn't being held by anything in a rotating reference frame it feels centrifugal and coriolis but not the centripetal.
 

Offline Geezer

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #36 on: 19/04/2012 23:51:54 »
Yes, but it's a real force that appears when you transform an inertial frame into a rotating reference frame such as that rotating with the surface of Earth.

When you do that, you get two effects, the Coriolis force which acts when things move around, and the centrifugal force which pushes things away from the axis of rotation even when they don't (relative to the surface of the Earth).

They come out of the same equation.

These are REAL effects that can kill you; just like gravity. They are as real as gravity. Coriolis force is a big effect in weather systems it's exactly as real as centrifugal effect.

I completely agree with you, but you are missing a very important point.
 
If you have translated everything into a rotating frame, it is not rotating. It is static, and everything else is rotating around it. If there is some force pushing you "outwards" it cannot be centrifugal, because you are not rotating. If you assume it is "centrifugal", you have just accepted that the real frame of reference is static and you are rotating within a different frame.
 
To properly use the Earth as a frame where all the forces are real, you have to account for the motions of all the other celestial bodies that you can observe. People tried that. It didn't work, so they expanded the frame to include the Solar system.........
 
 

Offline Geezer

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #37 on: 19/04/2012 23:59:21 »
No, you can have centrifugal without centripetal. When an object isn't being held by anything in a rotating reference frame it feels centrifugal and coriolis but not the centripetal.

There is no such thing as a rotating reference frame. There is only a reference frame. As soon as you assume the frame is rotating, you have just superimposed it on a different frame.
 
EDIT: BTW, the same thing is true of an "accelerating frame". If that is the frame, all phenomena better be described WRT that frame, otherwise they are bogus.
« Last Edit: 20/04/2012 00:40:22 by Geezer »
 

Offline Nizzle

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #38 on: 20/04/2012 06:17:18 »
I think if everyone called it the centrifugal pseudoforce instead of the centrifugal force, there wouldn't be an issue.
That's like saying that if everybody in the world became a Muslim then we'd have world peace.
Maybe, if all oil reserves in the world were empty as well ;)

There is no "flinging off". If gravity quit working, you would travel in a straight line tangential to the Earth's rotation.
Ignoring, of course, that without gravity, there would not be be an atmosphere, and the Earth would disintegrate. 

But, in your day without gravity.  Those people smart enough to tether themselves to Earth (for example tied to a tree), wouldn't find themselves flattened against the Earth with their rope at a tangent, but rather, they would find themselves hanging out at a perpendicular to Earth's rotation, at the end of their rope.  At the Equator, they would be hanging perpendicular to Earth.  At the 45th parallel, they would be hanging at a 45 degree angle from the surface.  You could say that the tree that a person is tied to is exerting centripetal force on that person.  Yet, what would you call the force the person is exerting on the tree, tending to pull out the roots?  And, what direction are the roots pulled out?

And lean towards the equator? I'm not so sure about that. If I visualize in my mind's eye a rotating earth with atmosphere and without gravity, I think the person at the 45th parallel would also be hanging straight up, with maybe a slight deviation from perpendicularity towards the position of the sun, ignoring the moon's gravity field since it will fly away if earth's gravity is gone ;)
 

Offline wolfekeeper

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #39 on: 02/08/2012 16:49:41 »
No, you can have centrifugal without centripetal. When an object isn't being held by anything in a rotating reference frame it feels centrifugal and coriolis but not the centripetal.
There is no such thing as a rotating reference frame. There is only a reference frame. As soon as you assume the frame is rotating, you have just superimposed it on a different frame.
If I've understood you correctly, that's last bit is right; a rotating reference frame is defined relative to an inertial reference frame. So you can have them; they are defined in a particular way.

They're also incredibly common; when you drive down the road at 30 miles per hour, that 30 miles per hour is relative to the rotating reference frame of the Earth!

The difference between a rotating reference frame and a reference frame can be detected using an accurate gyroscope.
 

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Re: Is it possible to make a lift/elevator to get into space?
« Reply #39 on: 02/08/2012 16:49:41 »

 

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