(split) Relativity on a plane

I meant the center of momentum of the two ball system. If you want to calculate the relativistic increase in gravitational attraction between the balls, I think you need to do it from that frame, no?

 

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Bull crap. I've disagreed with MD on a lot of things. He claims relativity is flat out wrong. He claims light only travels at c relative to an absolute rest frame. I know that's not how the real universe works.

As for your claim that I know nothing about relativity, you are simply wrong once again, as you so often are. Have you tried the bathroom scale experiment yet? I'm still waiting for you to post the two different scale readings that you were able to make the scale display at the same time.

 

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But you have the same exact misconceptions and the same exact total ignorance of the basics of SR.

Yet, in this thread you show total inability to understand the notion of relativistic measurements.

See, what did I tell you?

 

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So now you are claiming that the spring scale between the balls reads differently in different reference frames? Of course it doesn't. So we need to know which frame to calculate the force of attraction from. I think it's the frame in which the center of momentum of the 2-ball system is at rest.

 

See? It is exactly this type of arguing that convinces me that you are a Motor Daddy sockpuppet. You take your misunderstandings and you formulate as if they were claimed by someone else.

We do. You don't (and you are clearly unable to learn).

 

Wrong again. I can do Lorentz transforms, etc. I've never seen MD do them, because he thinks seems to think learning relativity would be a waste of time. Probably because of folks like yourself.

I think I understand them pretty well. I understand time dilation, length contraction, and relativity of simultaneity. I don't believe that a spring scale can provide two different measurements of force at one time, but relativity certainly never claimed that it could. That is your own idea.

You claimed ball A applies a different force to the scale than ball B applies to it. All in one reference frame!!! So why don't you go demonstrate that is possible, using your bathroom scale? Oh, that;'s right, because it's impossible.

 

Newton's law of gravity doesn't apply in Relativity, FYI. To say that the problem is with faster than light gravitational signals oversimplifies things. If you calculate the forces and accelerations from Newton's law in one frame, using the inertial masses and the distance between the two balls, and then do the same calculation from a boosted frame, the results don't transform consistently from one frame to the other.

 

Can you disengage your motor moth for a second and think about the fact that A doesn't move wrt his scale whilst B moves (at speed v)? Why would the forces be the same? Because you reason exactly like Motor Daddy?
You claimed that you understand Lorentz transforms, there is a whole introductory chapter that explains transformation of force. Instead of spending several days posting nonsense in this thread you could have gone and studied the respective chapter. Much better use for your time.

 

He's not assuming universal attraction per se. If he did, the two balls couldn't move the way they move in his silly exercise. He's assuming two identical forces that are orthogonal to the direction of motion.

 

But Newton's laws hold fairly well in each individual rest frame, right? All I was trying to do was calculate the force measurement that would be displayed on the spring scale between the two balls. This measurement could be taken in the frame of either ball, the situation is perfectly symmetrical.

The spring scale's size and mass are assumed to be negligible. At the instant when the two balls of identical mass and radius pass each other at a speed of \(v\) tangent to their surfaces, can you tell me what the gravitational force of attraction would be?

 

Yes, exactly. The moving ball could be guided by a straight track right up until the moment that it passes by the other ball. It's not a difficult arrangement.

 

The force applied to the scale by A must be equal and opposite to the force applied to the scale by B. Otherwise, there is a net force, which would cause the scale to accelerate. Go try it with your bathroom scale. Is that what you are claiming happens? The scale accelerates?

The Lorentz transforms I know transform coordinates, not forces.

 

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Scale A is comoving with ball A.
B is moving wrt A and the scale A.
How does B act on the scale at A? Through telepathic waves?

Scale B is comoving with ball B.
A is moving wrt B and the scale B.
How does A act on the scale at B? Through telepathic waves?

This kind of ignorance is your problem. Until you learn the appropriate chapter of SR, you will continue to spew nonsense.

 

Telepathic waves? LOL. So you still don't even understand the problem? The balls pass by each other close enough that the only thing that can fit between them is the extremely tiny, massless spring scale. You only need one scale; because of symmetry, there can be no difference in results obtained by two scales.

When ball B is located at:
\((x,y,z)=(0,2r,0)\)
and ball A is located at:
\((x,y,z)=(0,0,0)\)

The distance between the centers of the balls is exactly 2r which means the surfaces of the balls are virtually touching each other. That is, they would be touching if there hadn't been a tiny scale slipped between them. In other words, both balls touch the scale at the same time.

But you used the force transform when you presented your solution to this problem, and yet your solution did not make any sense. You arrived at the conclusion that the two balls apply different forces to the scales, according to each reference frame.

 

What, you can pick and choose which laws of physics are the same in all frames and which aren't? I thought all the laws of physics are supposed to be the same in all frames in SR?

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Since Tach is having trouble understanding the ball scenario, here is a drawing that might help. The red thing is the scale.

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Yeah, and that's why you can't use Newtonian gravity in SR (you can if you're describing non-relativistic objects), as they explain in undergrad.

 

Tough, you need to engage brain.

 

Tach, now that you can see this drawing:

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Do you still want to claim that the blue ball exerts a different amount of force on the scale than the green ball?