[Bill S]

Thanks Jartza.

Now we push the spot light, direction of the push is the direction of the light beam. When the spotlight is moving the distance between two randomly chosen photons grows slower, on the average, because the beam is a narrower beam now, in the F of R of the table.

I see this, but the spreading rate stays the same in the F of R of the spotlight, right?

[Bill S]

Jartza, I've been thinking (always dangerous) about your earlier comments.


1. “When a clock moves it is slow.”  In the F of  R of the observer.
2. “When a clock is shot from a cannon it slows down”  In the F of  R of the observer.
3. “Also when a gyroscope is shot from a cannon, it slows down.”  In the F of  R of the observer.
4. “But when a spinning cannon shoots a cannon ball, the cannon ball's spinning does not change.”  Why would it not change in the F of R of the observer?

[jartza]

4. “But when a spinning cannon shoots a cannon ball, the cannon ball's spinning does not change.”  Why would it not change in the F of R of the observer?

Very simple physics:
Cannon - cannon ball system's center of mass stays were it was, and cannon - cannon ball
system spins the same way as it did.

The spinning spring example maybe illustrates this better, the spring stays in the
same F of R, and spins as before.

BUT a gyroscope shot from a cannon slows down. Why is that? What is the difference? Now
there is something to think about.

[Ron Hughes]

Because of it's velocity with respect to the observer.

[Bill S]

Because of it's velocity with respect to the observer.

Would the same not apply to the canon ball?  The canon is spinning, but is otherwise stationary relative to the observer. After firing, the ball is spinning, but is travelling, relative to the observer, so its apparent rotation, in the F of R of the observer is slower.

[jartza]

Because of it's velocity with respect to the observer.

The gyroscope shot from a cannon spins slowly, because of its velocity with respect to the observer? OK I accept that.

Also a cannon ball shot from a spinning cannon spins slowly, because of its velocity with respect to the observer.

BUT the cannon ball shot from a spinning cannon spins at the SAME rate that it did spin when sitting in the barrel, in F of R of the observer.

Now this SAME rate is a slowed down rate, so when a observer starts chasing the cannon ball, the cannon ball's spinning speeds up in the
F of R of the accelerating observer.

I have been misleadingly saying the cannon ball's spinning is "not slowed down", I should have said that "it is the same as before" instead.

So the spinning of a flying gyroscope is slower than the spinning of a gyroscope sitting in the barrel, in the F of R of a still standing observer.

And the flying cannon ball's spinning rate is same as the spinning rate of the cannon ball sitting in the barrel, in the F of R of a still standing observer.

[jartza]

A little bit of maths about spinning cannons


rest spin of flying cannonball = rest spin of cannonball in the barrel + rest spin of gunpowder that disappears, or changes into energy


Rest spin meaning the angular momentum of an object in the F of R of the object.

[Bill S]

BUT the cannon ball shot from a spinning cannon spins at the SAME rate that it did spin when sitting in the barrel, in F of R of the observer.

When the canon ball was in the barrel, it, the canon and the observer were in the same inertial frame. Once fired, it is no longer in that inertial frame, so although its rotational rate, in its own F of R remains the same, it appears slower when viewed from the F of R of either the observer or the canon.  Right?

[jartza]

When the canon ball was in the barrel, it, the canon and the observer were in the same inertial frame. Once fired, it is no longer in that inertial frame, so although its rotational rate, in its own F of R remains the same, it appears slower when viewed from the F of R of either the observer or the canon.  Right?

Nope. If you go to the flying cannonball's frame to observe how fast it spins,
you will observe that firing increased the spinning rate.

And I mean AFTER the firing you go to the flying cannonball's frame.








 

[jartza]

What happens if a spinning cannon shoots a cannonball that is NOT spinning with the cannon?

Answer: cannonball starts to spin.
A torque is felt by the cannonball when it is put to spin.
Let's call this torque "time dilation torque", because this same torque is responsible for the slowing down of gyroscope that is shot from a cannon.

Now what if we accelerate ourselves into the flying gyroscope's F of R ?
Well, we observe that spinning of the gyroscope accelerates when we accelerate.
So we ask ourselves: what time dilation torque causes this acceleration of spinning?
To answer that we need general relativity. When we are accelerating we experience
there being a gravity field, and all the time that we are accelerating the gyroscope is losing its energy in this gravity field. Now it happens to be so that spinning objects always accelerate their spinning when losing energy in a gravity field, without feeling any torque.

So do we have time dilation of spin now figured out? Is there something to be explained left?

 

[Bill S]

Now what if we accelerate ourselves into the flying gyroscope's F of R ?
Well, we observe that spinning of the gyroscope accelerates when we accelerate.

I'm not clear what you are saying here.  Are you saying (1)that the spinning of the gyroscope accelerates relative to us as we accelerate in the course of moving ourselves into the F of R of the gyroscope; or (2)that it would accelerate if the whole system accelerated, after we had arrived in the gyroscope's F of R?

If (1), I see no problem.
If (2), why?

[jartza]

Now what if we accelerate ourselves into the flying gyroscope's F of R ?
Well, we observe that spinning of the gyroscope accelerates when we accelerate.

I'm not clear what you are saying here.  Are you saying (1)that the spinning of the gyroscope accelerates relative to us as we accelerate in the course of moving ourselves into the F of R of the gyroscope; or (2)that it would accelerate if the whole system accelerated, after we had arrived in the gyroscope's F of R?

If (1), I see no problem.
If (2), why?

I am saying number 1.

[jartza]

Are you guys following me in this spinning cannon story? Well here is a better story:
 

When we observe an accelerating spinning rocket whose exhaust is spinning like the rocket itself, we do not observe the spinning of the rocket slowing down or speeding up.

When we observe an accelerating spinning rocket whose exhaust is not spinning, because there are some kind of rudders at the nozzle, we observe that the spinning of the rocket speeds up.

When we observe an accelerating spinning rocket whose exhaust is spinning faster than the rocket itself, because there are some kind of rudders at the nozzle, that are adjusted to make the exhaust spin as mentioned, we observe that the spinning of the rocket slows down.

When we observe the first two rockets we see that they have a "speed limit", which is not c. Particularly rocket number two has a low speed limit, like 0.5 c. Rocket number three can achieve speeds arbitrarily close to c, relative to us.

[Bill S]

Jartza, I've just returned to this thread and read your last post, several times.  there are a couple of things I don't understand.
1. Why should the spinning/not spinning of the exhaust make a difference to our perception of the spinning of the rocket?
2. Why should these factors impose any speed limit (other than c) on the rocket? 

[jartza]

Jartza, I've just returned to this thread and read your last post, several times.  there are a couple of things I don't understand.
1. Why should the spinning/not spinning of the exhaust make a difference to our perception of the spinning of the rocket?

That's how rockets work: exhaust is accelerated this way, the rocket is accelerated the opposite way, this also applies to spinning motion.
(I thought saying "when x observes y then x observes z" was a good way to tell what the F of R is)

2. Why should these factors impose any speed limit (other than c) on the rocket? 

When a rocket is accelerated to near c, it is not possible to something inside the rocket to continue moving at speed near c.
When something inside a rocket has a speed near c, and it's not possible for that thing to slow down, then it's not possible to accelerate the rocket to near c.
And it's not possible to the spinning of a rocket to slow down without adjustable nozzles, or "rudders", or "spin adjustment rockets".





By the way, this whole thing is based on law of conservation of mass. They don't teach the law of conservation of mass at school. So maybe I should start a thread about conservation of mass.

[Bill S]

They don't teach the law of conservation of mass at school. So maybe I should start a thread about conservation of mass.

Yes,please.  Then I might not have to step up the Ginkgo biloba, just to get the hang of this spinning stuff. [:I]

[jartza]

Oh yes time dilation mechanism needs an explanation.


Let's attach some radioactive material on the center part of a big flywheel.
The radioactive stuff starts heating the flywheel. No heat is lost to anywhere else.
The flywheel is frictionless. Then we make the flywheel spin. What can we say about
the spinning rate?


Flywheel slows down, as heat mass-energy travels from center to periphery, it's the
Coriolis force thing.


Let's attach a spring on the center of a flywheel disk. Then we attach another disk
into the other end of the spring. Then we press the disks together. The spring becomes
compressed. Then we tie this thing with a string. This thing we have constructed is a
flywheel. It's frictionless flywheel. Now we make the flywheel spin. At some moment
the sting breaks. What can we say about the spinning rate, when the string breaks?


Flywheel slows down, it's the Coriolis force again. The mass-energy that was stored
in the spring travels from center to periphery of the flywheel.

Relativity says that when a flywheel is made to spin very fast the thermal motion
of molecules is slowed down, they call it time dilation. When thermal motion of the
molecules of a spinning flywheel increases the flywheel is slowed down, what do we
call this, reverse time dilation?

If I would claim that heat causes time dilation, then people in science forums would
say I'm nuts. So I claim that heat does NOT cause time dilation. So in the case
of a flywheel made of two parts, when these two parts are made to vibrate, then there
is no time dilation related to the motion. (The vibration energy is equivalent to heat
energy you see)

So the explanation of time dilation is that there is no time dilation, but there
are some cases when something slows down when something else speeds up.

[JP]

So the explanation of time dilation is that there is no time dilation, but there
are some cases when something slows down when something else speeds up.

 []

[jartza]

JP here's a question to you:

How do we accelerate a spinning object, so that we don't disturb the spinning?

(There are different ways, that have different effects on spinning rate)

[jartza]

One way to accelerate a flywheel is to put it in a rocket. In the rocket a clock slows down because of time dilation, and the flywheel slows down because of Coriolis force. If we eliminate the Coriolis force, a person with his brain slowing down observing a flywheel that is not slowing down, will say that "this flywheel is speeding up".