Gravity and Centrifugal Force do exist!

So why do you say they don't exist?

Because...they don't. 

Well, that doesn't answer my question. 

So, what makes you think the forces exist? What causes them? Every force must come from an external agent. So, I would like you to tell me where does the force of gravity and the centrifugal force come from.

When dealing with a noninertial reference frame, one must find a way to convert it to an inertial reference frame so we can use Newton's laws, because Newton's laws are only valid in an inertial frame.  There are two methods of accomplishing this.  One is by using pseudoforces.  The other is searching for another reference frame for which the motion is inertial.

As we have seen, including the existence of pseudoforces in a noninertial frame can convert it entirely into an inertial one.  We are now able to use the laws of physics to make accurate predictions about our formerly noninertial reference frame.

The second method, finding another reference frame for which motion is inertial, is the method I believe you are trying to advocate.  I think you are aware how it works.  For circular motion, you simply shift to a non-rotating frame and you can explain the motions such as a ball flying off in a straight line quite easily.  Gravitation is a little more tricky.  You shift to a reference frame in non-Euclidian space such that the motion we observe, such as orbits of planets, is inertial.  This is just general relativity

Both of these methods of transforming a noninertial frame into an inertial one are equally valid.  One method may be simpler and more enlightening than the other, such as the case with gravitation, but both methods are equally capable of accurate predictions.  So which method is superior?  Which method has more right to "existence"?  A pseudoforce no more exists than the space-time manifold of general relativity.  They are both just constructs of our minds to explain the motions we observe.

When dealing with a noninertial reference frame, one must find a way to convert it to an inertial reference frame so we can use Newton's laws, because Newton's laws are only valid in an inertial frame.  There are two methods of accomplishing this.  One is by using pseudoforces.  The other is searching for another reference frame for which the motion is inertial.

There ya go. You finally explained the centrifugal force and gravity force do not exist.

As we have seen, including the existence of pseudoforces in a noninertial frame can convert it entirely into an inertial one.  We are now able to use the laws of physics to make accurate predictions about our formerly noninertial reference frame.

The second method, finding another reference frame for which motion is inertial, is the method I believe you are trying to advocate.  I think you are aware how it works.  For circular motion, you simply shift to a non-rotating frame and you can explain the motions such as a ball flying off in a straight line quite easily.  Gravitation is a little more tricky.  You shift to a reference frame in non-Euclidian space such that the motion we observe, such as orbits of planets, is inertial.  This is just general relativity

Both of these methods of transforming a noninertial frame into an inertial one are equally valid.  One method may be simpler and more enlightening than the other, such as the case with gravitation, but both methods are equally capable of accurate predictions.  So which method is superior?  Which method has more right to "existence"?  A pseudoforce no more exists than the space-time manifold of general relativity.  They are both just constructs of our minds to explain the motions we observe.

Right, since pseudo-forces arise in shifting frames of reference (in order to become valid), they cannot possibly exist as real forces. Anyway, either we agree the forces do not exist or you can answer my questions above, which you still haven't.

You obviously misunderstood what I wrote, but I'll answer your question anyway.

So, what makes you think the forces exist? What causes them? Every force must come from an external agent. So, I would like you to tell me where does the force of gravity and the centrifugal force come from.

You've got a valid question.  If a force is acting on object, another object must cause the force, right?  With gravity, you can attribute the cause of the force to another mass.  Mass attracts mass.  For centrifugal and coriolis forces, there is some debate as to what causes them, but apparently the rest of the universe does.  Read an article on Newton's Bucket argument and Mach's principle such as this one: http://www-groups.dcs.st-and.ac.uk/~history/PrintHT/Newton_bucket.html

But this is irrelevant to the argument I am trying to make.

I am merely saying that pseudoforces and changing reference frames are equally valid methods of converting from noninertial frames to inertial frames.  Since all inertial reference frames are equivalent, what makes either method superior to the other?  A pseudoforce exists no more or less than the other inertial reference frame you switch to when dealing with circular motion and gravity.

Right, since pseudo-forces arise in shifting frames of reference (in order to become valid), they cannot possibly exist as real forces.

Pseudoforces are different from other forces (electromagnetism, friction and such) since they depend on your frame of reference.  But how does that make them not exist?  They certainly exist in the inertial frame of reference you have chosen for them.  That's all that matters.

You've got a valid question.  If a force is acting on object, another object must cause the force, right?  With gravity, you can attribute the cause of the force to another mass.  Mass attracts mass. 

What about objects that have no mass?  Do objects simply turn off this force if there were no other mass in the universe?

Pseudoforces are different from other forces (electromagnetism, friction and such) since they depend on your frame of reference.  But how does that make them not exist?

They don't exist as forces.  They only arise when you look at yourself in the wrong frame of reference.  You must invent a force to resolve your observations.  Pseudo forces don't actually exist as forces.  They only appear to be forces.  There is no force acting on an object experiencing gravity.  It just appears to be behaving as though acted on by a force, to us.

You obviously misunderstood what I wrote, but I'll answer your question anyway.

You said shifting frames of reference is one of the methods to deal with pseudo-forces. Thus, they cannot exist as real forces.

You've got a valid question.  If a force is acting on object, another object must cause the force, right?

Right.

With gravity, you can attribute the cause of the force to another mass.  Mass attracts mass.

No, gravity does not exist. Mass never attracts mass. Inverse square law is no longer valid in modern science.

For centrifugal and coriolis forces, there is some debate as to what causes them, but apparently the rest of the universe does.

There's no need of debate, as these forces never exist as real. Take some general relativity and you will know they are inertial-forces proportional to inertial masses, which means they don't exist.

I am merely saying that pseudoforces and changing reference frames are equally valid methods of converting from noninertial frames to inertial frames.  Since all inertial reference frames are equivalent, what makes either method superior to the other?  A pseudoforce exists no more or less than the other inertial reference frame you switch to when dealing with circular motion and gravity.

Right, since you must shift frames of reference to deal with these forces, they are considered pseudo-forces. Since pseudo-forces exist only in inertial frames of reference, when one observer enters a non-inertial frames of reference, they cease to exist. These forces are what the observer feels when accelerating. Relative to a stationary observer, nothing is exerted on the accelerating observer.

Pseudoforces are different from other forces (electromagnetism, friction and such) since they depend on your frame of reference.  But how does that make them not exist?  They certainly exist in the inertial frame of reference you have chosen for them.  That's all that matters.

You still don't understand. If pseudo-forces only exist in inertial frames of reference, they cannot possibly exist as real forces.

What about objects that have no mass?

Like light?  Light has energy, so by mass-energy equivalence there is a mass you can associate with it called its relativistic mass.  Thus, light can be acted upon by a force even though its component photons have no rest mass.

Do objects simply turn off this force if there were no other mass in the universe?

Mach's principle seems to imply that the answer is yes.

You must invent a force to resolve your observations.

Do you also not have to "invent" another reference frame such that the observed motion is inertial?  That's what Einstein spent a decade doing with general relativity.

They only arise when you look at yourself in the wrong frame of reference.

How do you know what the "right" reference frame is?  Adding pseudoforces and transforming to other reference frames are equally valid methods of arriving at inertial reference frames.  Since all inertial frames are equivalent, which method is more right?

Like light?  Light has energy, so by mass-energy equivalence there is a mass you can associate with it called its relativistic mass.  Thus, light can be acted upon by a force even though its component photons have no rest mass.

Why do you leave them out of the whole gravity equation, then?  Are they not special enough to cause gravity too?  Or do you only apply physics to certain things?

Do objects simply turn off this force if there were no other mass in the universe?
Mach's principle seems to imply that the answer is yes.

Mach's principle does not.

Do you also not have to "invent" another reference frame such that the observed motion is inertial?  That's what Einstein spent a decade doing with general relativity.

Inventing inertial frames from non inertial ones is what causes the problem.

How do you know what the "right" reference frame is?

It's the one without the pseudo forces.

Adding pseudoforces and transforming to other reference frames are equally valid methods of arriving at inertial reference frames.  Since all inertial frames are equivalent, which method is more right?

Adding pseudo forces to a transformed frame of reference is quite valid.  That does not in any way turn pseudo forces into real ones.

Quote from: epsilon on Today at 02:46:03 PM
Like light?  Light has energy, so by mass-energy equivalence there is a mass you can associate with it called its relativistic mass.  Thus, light can be acted upon by a force even though its component photons have no rest mass.

Why do you leave them out of the whole gravity equation, then?  Are they not special enough to cause gravity too?  Or do you only apply physics to certain things?

What gravity equation?  Newton's law of universal gravitation?  We both know that it is incorrect.  Are you trying to ask whether light can cause gravity or not?  Why not?  It has relativistic mass.

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How do you know what the "right" reference frame is?
It's the one without the pseudo forces.

An inertial frame without pseudoforces is just as right as one with pseudoforces.

Inventing inertial frames from non inertial ones is what causes the problem.

Can you explain please?

Adding pseudo forces to a transformed frame of reference is quite valid.  That does not in any way turn pseudo forces into real ones.

Yup.  It's perfectly legitimate to use pseudoforces as if they were real forces in the reference fame you are working in.  I am trying to argue that this is just as legitimate as shifting to another frame.  Just because pseudoforces don't act like other forces in that they depend on one's frame of reference, how does that make them not exist?

Excellent debate.

Yup.  It's perfectly legitimate to use pseudoforces as if they were real forces in the reference fame you are working in.

...Which is why they are not considered real...

I am trying to argue that this is just as legitimate as shifting to another frame.  Just because pseudoforces don't act like other forces in that they depend on one's frame of reference, how does that make them not exist?

No, pseudo-forces work exactly the same as real forces.  The only reason why they don't exist is that they are only valid in inertial frames of reference.

No, pseudo-forces work exactly the same as real forces.

When did I say they didn't work the same as real forces?

The only reason why they don't exist is that they are only valid in inertial frames of reference.

What?

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No, pseudo-forces work exactly the same as real forces.

When did I say they didn't work the same as real forces?

When did I say you say they didn't work the same as real forces?

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The only reason why they don't exist is that they are only valid in inertial frames of reference.

What?

So, in what frames of reference do Newton's gravity and his laws of motion become valid again?

So, in what frames of reference do Newton's gravity and his laws of motion become valid again?

Inertial ones.  What's your point?

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So, in what frames of reference do Newton's gravity and his laws of motion become valid again?

Inertial ones.  What's your point?

...that they are only valid in inertial frames of reference... Hence, they are considered fictitious.

What gravity equation?  Newton's law of universal gravitation?  We both know that it is incorrect.  Are you trying to ask whether light can cause gravity or not?  Why not?  It has relativistic mass.

What would happen if you slowed down light?

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Inventing inertial frames from non inertial ones is what causes the problem.

Can you explain please?

Taking a non inertial frame of reference and making it inertial is what gives us our fictitious forces.  Such as with gravity.  We are undergoing a constant acceleration, but we perceive ourselves to be at rest.  Thereby, changing our non inertial FoR into an inertial one.  In doing this transformation, we see that objects appear to accelerate towards the ground.  Since we are in an inertial FoR, we assume Newton's first two laws of inertia apply, so we assume there must be a force acting on the object, making it accelerate.  However, if we look at it outside of our inertial FoR, we would see that the object is the inertial one and we are non inertial.

Just because pseudoforces don't act like other forces in that they depend on one's frame of reference, how does that make them not exist?

How does a fictitious force become a real force?

What would happen if you slowed down light?

Light is peculiar.  It always travels at c.  However, a force does work on light by changing its energy and hence wavelength.

Taking a non inertial frame of reference and making it inertial is what gives us our fictitious forces.  Such as with gravity.  We are undergoing a constant acceleration, but we perceive ourselves to be at rest.  Thereby, changing our non inertial FoR into an inertial one.  In doing this transformation, we see that objects appear to accelerate towards the ground.  Since we are in an inertial FoR, we assume Newton's first two laws of inertia apply, so we assume there must be a force acting on the object, making it accelerate.  However, if we look at it outside of our inertial FoR, we would see that the object is the inertial one and we are non inertial.

Yeah, that's right, but why is dealing with pseudoforces problematic?  Why should it matter whether I choose a reference frame with pseudoforces or not?

How does a fictitious force become a real force?

A ficticious force is a real force in the reference frame you have chosen for it.  If it acts like a force why can't it be considered a force?

A ficticious force is a real force in the reference frame you have chosen for it.  If it acts like a force why can't it be considered a force?

A force will be a force no matter what FoR you choose. If you can make it disappear by changing your FoR, then it's a pseudo-force; it doesn't exist as a real force.

It's really not that complicated. If you're going to speak of gravity as a force, at least acknowledge that's it's fictitious and we can end the debate.

Light is peculiar.  It always travels at c. 

Ok, so what would happen if you slowed it down?  What would happen to its relativistic mass?  What equations even use relativistic mass in determining 'gravity'?

Yeah, that's right, but why is dealing with pseudoforces problematic?  Why should it matter whether I choose a reference frame with pseudoforces or not?

I did not say that having pseudo forces was problematic, I said the transformation of FoRs is what was causing our problem, as in, our debate.

A ficticious force is a real force in the reference frame you have chosen for it.  If it acts like a force why can't it be considered a force?

I'll ask again:  How can a fictitious force become a real force?

I'll ask again:  How can a fictitious force become a real force?

Pinocchio.

Quote from: TheEngineer on December 25, 2007, 05:23:43 AM

I'll ask again:  How can a fictitious force become a real force?

Pinocchio.

Or leprechauns. Don't forget them

Ok, so what would happen if you slowed it down?

What does this have to do with anything?  How is that even possible?

I did not say that having pseudo forces was problematic, I said the transformation of FoRs is what was causing our problem, as in, our debate.

Pseudoforces cannot be completely explained as mere relics of transformation from one frame of reference to another.

How can a fictitious force become a real force?

My entire point is that 'fictitious' forces are real forces.

My entire point is that 'fictitious' forces are real forces.

Wow.  Your entire point is wrong then.

rofl

My entire point is that 'fictitious' forces are real forces.

EPSILON'S EQUIVALENCE PRINCIPLE:

Fake = Real

Would someone please explain what they mean by fictious forces?

Centrifugal force is not a force, it is you trying to go straight out and escape this circular motion.  Nothing is pushing or pulling on you.

Gravity is an imaginary force that can be created in a non-inertial frame of reference, similar to centrifugal force.

But I want to go along the tangent of the circle, and not along its radius. And another thing, what do you mean by a non-inerital reference frame?