# (split) Relativity on a plane

Valued Senior Member
Here's a thought experiment along those lines.

Say a plane is at rest on a runway that is at absolute rest. It accelerates up up and away to a constant velocity of 500 MPH and remains cruising at that velocity.

There is a person at the midpoint of the plane and a person with a ball at each end of the plane. Simultaneously each person accelerates their ball towards the mid point person. They each applied the same amount of force to the ball. The balls hit the midpoint person simultaneously.

The midpoint person says the balls were traveling in different directions at the the same velocity towards each other before they impacted him at the velocity of 100 MPH. He could not be more wrong. That is his illusion.

The person at the rear of the plane accelerated the ball to a velocity of 600 MPH, and the person at the front of the plane accelerated the ball to a velocity of 400 MPH. Both balls were traveling in the same direction at different velocities when they hit the midpoint observer.

The only way the balls could have been traveling in opposite directions is if the plane (mid point person) was at an absolute zero velocity.

Here's a thought experiment along those lines.

Say a plane is at rest on a runway that is at absolute rest. It accelerates up up and away to a constant velocity of 500 MPH and remains cruising at that velocity.

There is a person at the midpoint of the plane and a person with a ball at each end of the plane. Simultaneously each person accelerates their ball towards the mid point person. They each applied the same amount of force to the ball. The balls hit the midpoint person simultaneously.

The midpoint person says the balls were traveling in different directions at the the same velocity towards each other before they impacted him at the velocity of 100 MPH. He could not be more wrong. That is his illusion.

The person at the rear of the plane accelerated the ball to a velocity of 600 MPH, and the person at the front of the plane accelerated the ball to a velocity of 400 MPH. Both balls were traveling in the same direction at different velocities when they hit the midpoint observer.

The only way the balls could have been traveling in opposite directions is if the plane (mid point person) was at an absolute zero velocity.
Just think what the velocities would be if he earth was in motion. It is amazing what we can do working with reference frames, isn't it?

The midpoint person says the balls were traveling in different directions at the the same velocity towards each other before they impacted him at the velocity of 100 MPH. He could not be more wrong. That is his illusion.

The person at the rear of the plane accelerated the ball to a velocity of 600 MPH, and the person at the front of the plane accelerated the ball to a velocity of 400 MPH. Both balls were traveling in the same direction at different velocities when they hit the midpoint observer.

The only way the balls could have been traveling in opposite directions is if the plane (mid point person) was at an absolute zero velocity.

Ha! I always knew Heathrow Airport was the centre of the universe, not just the British Empire!

Just think what the velocities would be if he earth was in motion. It is amazing what we can do working with reference frames, isn't it?
Not to mention the solar system, Orion spiral arm and galactic motion.

It doesn't. The fact that MD's world contradicts reality is not his concern, he's not worried about being out of touch with reality.
He'll continue to post his tripe undisturbed by the physical reality.

Seriously, the covariance of the physics laws is a fundamental property of our reality.
For example , the covariant formulation of Newton law is not $$F=ma$$ but $$F=\frac{dp}{d\tau}$$ and it holds in all the frames of reference.

Seriously, Tach, do you even know what force is? Do you understand that f=ma is a net force, and that acceleration is simply the rate of change of velocity, which is simply the measure of distance and time an object travels?

Seriously, Tach, do you even know what force is? Do you understand that f=ma is a net force, and that acceleration is simply the rate of change of velocity, which is simply the measure of distance and time an object travels?

What does all this have to do with your manifest inability to understand covariance?
So far you restricted your ignorance to the thread demonstrating your inability to learn simple kinematics, why do you feel compelled to prove your ignorance in dynamics?

What does all this have to do with your manifest inability to understand covariance?

Well you use terms that you don't understand.

Describe force to me, in your own words. Give an example of force and an example of a measurement of force. Use a torque wrench for your example if you can. If the torque wrench reads 100 lb-ft of torque, and the wrench is 2 ft long, and you apply a force to the handle, how much force did you apply?

Do you understand mechanical advantage? How about how a gear ratio affects the torque and RPM of an output shaft? If the gear ratio is 10:1, and the torque on the output shaft is 1000 lb-ft, how much torque is on the input shaft, and how much force is on the handle of the torque wrench attached to the input shaft if the force is applied to the handle 2 feet away from the shaft?

Get a clue!

Describe force to me, in your own words. Give an example of force and an example of a measurement of force. Use a torque wrench for your example if you can. If the torque wrench reads 100 lb-ft of torque, and the wrench is 2 ft long, and you apply a force to the handle, how much force did you apply?

First, I am sure that you think a problem involving a torque wrench is terribly difficult, but that is really, really basic physics.

Secondly, why would anyone waste time on one of your silly problems, your history tells us exactly what would happen - you would either misinterpret it or ignore it, and then of course QW would swoon over whatever absurdity you spouted. You guys are starting to kinda freak me out a bit {shudder}.

If the torque wrench reads 100 lb-ft of torque, and the wrench is 2 ft long, and you apply a force to the handle, how much force did you apply?

I didn't apply any force personally since I don't engage in your childish games.
The force applied in your childish exercise is 50 lb. What does all this have to do with your ignorance about covariance? Why are you spamming this thread with your stupidities? Got tired of the beatings you are taking from JamesR and przyck in the other thread on basic kinematics and you decided to try your luck in dynamics?

Two people are weighed to be exactly 200 lbs. There is a teeter totter on the plane. The people get on the plane and accelerate to .9c. The teeter totter is inline with the motion of the plane. The teeter totter is rigged to measure the torque on each side. The people sit 4 feet away from the fulcrum on the teeter tooter.

200 lbs*4 feet=800 lb-ft of torque on each side.

Einstein says the length of the tooter is contracted.

What does the totter read on earth and what does the totter read at .9c?

Torque is torque, and a shorter totter means less torque.

Meh

The torque is
$$R=LxF$$

In the moving frame :

$$L'=L/\gamma$$

$$F'=F \gamma$$

Therefore:

$$R'=L'xF'=LxF=R$$

This means that you are still the village idiot.

So the torque is different in each frame because the length is different in each frame. There goes the laws of physics being the same in all frames! One totter and two people and you get as many different torques as different frames. That is obviously not the real world, as in the real world, there is one torque value!

What sort of idiot are you?

Again, since maybe you didn't understand.

If each frame sees the length as different, each frame sees a different torque.

...and if you want to get more technical about the torque, we can place two different weight people on the totter and measure the rotational acceleration and torque at RPM, and find out who is talking smack and doesn't know their head from a hole in the ground.

The length contracts but the force changes as well. You can't read simple math, can you?

So you are saying that at each different velocity the torque will be different due to the difference in length?

So your position is every frame agrees the torque is 800 lb-ft, and the length is 4 ft??
No. My position is that you are an idiot who can't read, can't comprehend and whose condition cannot be cured.

No. My position is that you are an idiot who can't read, can't comprehend and whose condition cannot be cured.

So in the plane frame, the torque is 800 lb-ft, but in the earth frame the torque is less than 800 lb-ft, because the earth frame sees the totter as contracted. I'll take that as your final answer.

So you've shown that torque is not the same in all frames, hence rotational acceleration can't be the same in all frames. So not only do Einstein's observers disagree on lengths and times, they also disagree on torque, force, and rotational acceleration.

What do Einstein's observers agree on that supports the idea that all the laws of physics are the same in all frames? They don't agree on anything, mass, distance, or time!

They agree that the relationships between all the variables will be the same. The same formulas will work in each frame.

Not if length is contracted in one direction and not the other direction in the same frame.

Say the totter is inline with the motion of the plane and the plane observer says the torque is 800 lb-ft. Then he rotates the totter 90 degrees so the totter is perpendicular to the motion. He says the torque is still 800 lb-ft.

But the earth observer does not agree that the torque is 800 lb-ft each way, because the length is contracted one way and not the other way.

He can not come to the same conclusion each way using the same torque=force*distance formula, as the distance is different one way vs the other way. The mass of the people doesn't change when the totter is rotated, but the distance does, so the torque is different each way.

So in the plane frame, the torque is 800 lb-ft, but in the earth frame the torque is less than 800 lb-ft, because the earth frame sees the totter as contracted. I'll take that as your final answer.

So you've shown that torque is not the same in all frames, hence rotational acceleration can't be the same in all frames.

MD, didn't you see where Tach showed you that the torque is the same in all frames? Look again:

The torque is
$$R=LxF$$

In the moving frame :

$$L'=L/\gamma$$

$$F'=F \gamma$$

Therefore:

$$R'=L'xF'=LxF=R$$

He is saying that the length is contracted by a factor of gamma:
$$L'=L/\gamma$$

And the force is increased by a factor of gamma:
$$F'=F \gamma$$

MD, didn't you see where Tach showed you that the torque is the same in all frames? Look again:

He is saying that the length is contracted by a factor of gamma:
$$L'=L/\gamma$$

And the force is increased by a factor of gamma:
$$F'=F \gamma$$

How is the force increased?

How is the force increased?

I don't know, but I imagine that magic is involved. You'll have to ask Tach.