# (split) Relativity on a plane

If I'm a moving observer in a boosted frame (we really should use the boost lingo more often here), I can still legitimately argue that two scales read the same value while experiencing different forces as seen from my POV. I see two different forces, and two different scale inertias, leading to the same reading on both scales. All that matters is the forces are the same in the rest frame.

Yes, but Tach is saying there are two different forces applied to the spring scale in one frame. Either of the balls can be considered to be the rest frame, and he has two different forces in both frames.

Yes, but Tach is saying there are two different forces applied to the spring scale in one frame. Either of the balls can be considered to be the rest frame, and he has two different forces in both frames.

"Captn", he's all yours, have fun! He is as dense as MD, so good luck!

How does the scale located at A measure the force applied at B when A and B are in relative motion?
You don't need to answer the above, it is clear, you are Motor Daddy's brother.

Now you claim it is impossible to measure the weight of a moving object? Yeah, we should all forget about your failed calculations showing two different forces of attraction in each frame, because it is impossible to measure the weight of moving objects!!! Good one!

I never imagined that there could be two "Motor Daddys" in the same forum but there are! Do you want to take over? I am getting bored and tired.

You're probably just getting tired of being proven wrong.

Ned, I said earlier in this thread that Tach doesn't understand what force is, and I stand by that statement.

"Captn", he's all yours, have fun! He is as dense as MD, so good luck!

Get a clue, Tach. When you understand the difference between torque and force then we can finish this discussion.

Ned, I said earlier in this thread Tach doesn't understand what force is, and I stand by that statement.

He did mix up force and torque earlier, among other things. But I think his big mistake is that he is blindly applying an SR transformation of forces (without regard for the fact that the force we are concerned with is a weight). In the case of the airplane flying over the runway, the weights are a force of attraction between the two frames. Obviously the runway frame is fixed to the earth, and the flying plane is not.

Again, I don't need to use weight to apply the force to the handles of the torque wrenches, I can use adjustable length bars bolted to the floor. I can apply an equal force to the handles in the plane, and the runway observer will be forced to say the torques are different than each other due to the length contraction of the x axis torque wrench.

Why is that so important? Because the plane observer will claim there is a zero net force and the runway observer will claim a net force greater than zero. Acceleration is proportional to net force! One observer says there is an acceleration and the other says not.

Why is that so important? Because the plane observer will claim there is a zero net force and the runway observer will claim a net force greater than zero. Acceleration is proportional to net force! One observer says there is an acceleration and the other says not.

Please restate your wrench problem in its latest incarnation, and why you think a non-zero force in one frame translates to zero force in another.

Please restate your wrench problem in its latest incarnation, and why you think a non-zero force in one frame translates to zero force in another.

Before I do, do you think it's OK for one frame to claim that the torque wrenches read the same as each other, and for the other frame to claim the torque wrenches read different than each other?

Before I do, do you think it's OK for one frame to claim that the torque wrenches read the same as each other, and for the other frame to claim the torque wrenches read different than each other?

If two wrenches are located at the same position at the same time as seen in one reference frame, and they both have a gauge of some kind which reads off their respective torques, then the boosted frame will see these wrenches give off the same reading, corresponding to torque they exert in the rest frame, whereas the actual torques themselves will be measured to be different as seen in the moving frame. It depends on whether the scales are moving or not.

If two wrenches are located at the same position at the same time as seen in one reference frame, and they both have a gauge of some kind which reads off their respective torques, then the boosted frame will see these wrenches give off the same reading, corresponding to torque they exert in the rest frame, whereas the actual torques themselves will be measured to be different as seen in the moving frame. It depends on whether the scales are moving or not.

What? Can you clear that up for me?

What? Can you clear that up for me?

What's there to clear up? I can see two force meters give the same reading, that doesn't mean the actual forces in my frame are the same as what those meters indicate, since the meters are measuring in the non-boosted frame.

What's there to clear up? I can see two force meters give the same reading, that doesn't mean the actual forces in my frame are the same as what those meters indicate, since the meters are measuring in the non-boosted frame.

I'd love to see an example of taking such a measurement simultaneously from two different frames. The only example I can think of is my spring scale idea, but that is a special case, because it measures a force that bridges across both frames.

I'd love to see an example of taking such a measurement simultaneously from two different frames.

I'm sure there are tons of examples to be found. If forces didn't translate according to the way Relativity specifies, we wouldn't find relativistic particles accumulate the energies they do as they approach the speed of light- as you get closer to c, the force you have to apply to keep it accelerating rises asymptotically. $$E=mc^2$$ is a direct consequence of the Relativistic force law.

There are probably known examples of force transformations involving the electromagnetic interactions between two relativistic currents moving in opposite directions. Instead of having to adjust the reference frame, you could start with one current at rest (a collection of charges) and one current moving near $$c$$, then reverse the situation, and compare the forces the beams/charges experience in each case by watching how much they deflect.

Hmm, I've been think more on the subject of relativistic mass increase. I read somewhere that you have to find the center of momentum of a system in order to apply it. If that is the case, then the $$\gamma$$ in my scenario with two balls and a spring scale should be calculated from a third reference frame in which both balls are moving at the same speed in opposite directions. This must be the case, otherwise you can calculate different forces of attraction in different reference frames. Ha! I solved it! Take that, Tach! LOL!!!

I'd love to see an example of taking such a measurement simultaneously from two different frames. The only example I can think of is my spring scale idea, but that is a special case, because it measures a force that bridges across both frames.

It applies to all physical entities, em field, charge, energy, momentum, force , acceleration, speed. It is called "relativity". I have become convinced that you are nothing but a Motor Daddy sockpuppet, the odds for different people to mangle relativity to the same exact extent are null.

otherwise you can calculate different forces of attraction in different reference frames.
...which is precisely what SR does but you and your sockpuppet can't seem to accept.

Hmm, I've been think more on the subject of relativistic mass increase. I read somewhere that you have to find the center of momentum of a system in order to apply it. If that is the case, then the $$\gamma$$ in my scenario with two balls and a spring scale should be calculated from a third reference frame in which both balls are moving at the same speed in opposite directions.

Nope. If you want to calculate the mass of a ball (known as the "invariant mass" in Relativity), the ball's center of momentum frame is the same as its rest frame.

I'm sure there are tons of examples to be found. If forces didn't translate according to the way Relativity specifies, we wouldn't find relativistic particles accumulate the energies they do as they approach the speed of light- as you get closer to c, the force you have to apply to keep it accelerating rises asymptotically. $$E=mc^2$$ is a direct consequence of the Relativistic force law.

There are probably known examples of force transformations involving the electromagnetic interactions between two relativistic currents moving in opposite directions. Instead of having to adjust the reference frame, you could start with one current at rest (a collection of charges) and one current moving near $$c$$, then reverse the situation, and compare the forces the beams/charges experience in each case by watching how much they deflect.

Is there a simple way to apply those ideas to, say, Motor Daddy's airplane example? I'd like to see a force transformation actually make sense. Tach's approach did not make any sense, because he didn't realize he was working with a force that spanned from one frame to the other. I'd like to see how it is really supposed to work.