# Discussion:Zero Doppler effect for reflected light from a rolling wheel

Has Tach realized yet that the problem in his interpretation of the problem is the fact that in the rest frame of the camera and the light source, the instaneous velocity of the mirror, and the tangential velocity of the mirror are only paralell at two points on the circumference of the wheel (or tube), and so there are only two locations in the cycle where the mirrors instantaneous velocity is paralell to the tangent plane, and so there are only two locations where there is no doppler shift?

Has Tach realized yet that the problem in his interpretation of the problem is the fact that in the rest frame of the camera and the light source, the instaneous velocity of the mirror, and the tangential velocity of the mirror are only paralell at two points on the circumference of the wheel (or tube), and so there are only two locations in the cycle where the mirrors instantaneous velocity is paralell to the tangent plane, and so there are only two locations where there is no doppler shift?

I don't think he has. I could have missed on a few posts though of him back-tracking... it is afterall, hard to keep track when this occurs.

The methods you presented are wrong.

Does this really need explaining?
Try here

Yes, I thought that you made this mistake, the Lorentz transforms do not transform a right angle into a right angle, You made the obvious mistake of considering the angle between the surface normal and the velocity vector. While the angle is $$\pi/2$$ in the axle frame, it is LESS than $$\pi/2$$ in any other frame. Had you considered the angle between the tangent to the plane and the velocity, you would have avoided the goof.

No, you did not.

Of course I did, this is how I knew you were wrong. Besides, I notice that for all your bluster, you did no derivation whatsoever.

No, this is a qualitatively different situation to that described by the aberration formula.

Yet, if what you were claiming were true , it would apply to the angle between a ray of light (representing vector 1) and the direction source - observer (representing vector 2). The aberration formula preservers angles multiple of $$\pi$$, your erroneous claim would invalidate it.
For example, if you start from $$cos \theta'=\frac{cos \theta +v/c}{1+ v/c. cos \theta}$$

and you make

1. $$\theta=\pi/2$$ you get
$$cos \theta' =v/c$$, so, $$\theta'< \pi/2$$

2. $$\theta=0$$ you get
$$cos \theta' =1$$, so, $$\theta'=0$$

Hang tight while I translate to tex...
(May not be until tomorrow. I'm supposed to be pulling up carpet today.)

Wait a sec, for two days you were chomping at the bit to "show me" how to do the angle transformations, now that I showed you where you made the mistake you need more time "to translate to tex"? I thought you were itching to prove me wrong and that you had all the calculations at your fingertips.

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Has Tach realized yet that the problem in his interpretation of the problem is the fact that in the rest frame of the camera and the light source, the instaneous velocity of the mirror, and the tangential velocity of the mirror are only paralell at two points on the circumference of the wheel (or tube), and so there are only two locations in the cycle where the mirrors instantaneous velocity is paralell to the tangent plane, and so there are only two locations where there is no doppler shift?

Of course I realize that this claim is false. This is precisely the nature of my debate with pete.

Of course I realize that this claim is false. This is precisely the nature of my debate with pete.

Oh right. So we've moved on from that... nice recovery!

Of course I realize that this claim is false. This is precisely the nature of my debate with pete.

Now, here's (part of) what I asserted in my question:

...the instaneous velocity of the mirror, and the tangential velocity of the mirror are only paralell at two points on the circumference of the wheel...

Versus:
...Had you considered the angle between the tangent to the plane and the velocity, you would have avoided the goof...
:shrug:

Now, here's (part of) what I asserted in my question:

Versus:

:shrug:

Yes, I considered it and I discarded as false. If you followed my exchange with pete I have shown him three times, through three different methods that the claim is false. Each time, through direct calculation. pete, on the other hand, produced none, I am still waiting for his proof but I already have a very good indication of what he did wrong: he tried to Lorentz-transform the angle between the surface velocity and the normal vector to the surface and he got the surprise of finding out that it isn't frame-invariant (it is dependent on the relative speed between frames).

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Yes, I considered it and I discarded as false. If you followed my exchange with pete I have shown him three times, through three different methods that the claim is false. Each time, through direct calculation. pete produced none, I am still waiting for his proof but I already have a very good indication of what he did wrong.

You know tach... showing you know what went wrong, speaks greater words of your credibility that simply beating around the bush.

just saying....

You know tach... showing you know what went wrong, speaks greater words of your credibility that simply beating around the bush.

just saying....

Let me elaborate why...

... say you don't actually say anything at all. You only claim to know what is really wrong. Then when someone comes along and shows the example wrong, no one will believe you actually knew what was wrong in the first place. You hadn't shown any evidence to the contrary, so why would anyone take your claims of knowing better seriously?

That is why, cut with the **** and straight to the point. It will show people exactly how much you can be relied on, otherwise it is all good as chinese whispers.

I am just informing everyone that Tach has now (a good while after my comment above) edited his post by including the reason for Pete's and Tach's incongruity:

''he tried to Lorentz-transform the angle between the surface velocity and the normal vector to the surface and he got the surprise of finding out that it isn't frame-invariant (it is dependent on the relative speed between frames). ''

I really wish he would learn to give a heads up when he does something like this. I find it very distasteful!

I am just informing everyone that Tach has now (a good while after my comment above) edited his post by including the reason for Pete's and Tach's incongruity:

''he tried to Lorentz-transform the angle between the surface velocity and the normal vector to the surface and he got the surprise of finding out that it isn't frame-invariant (it is dependent on the relative speed between frames). ''

I really wish he would learn to give a heads up when he does something like this. I find it very distasteful!

You realize that no one is paying any attention to you? Especially after your fiasco with your "Black hole" essay.....

You realize that no one is paying any attention to you? Especially after your fiasco with your "Black hole" essay.....

You truely are an idiot. You are stating so many ''things'' are wrong in that thread. I don't know why you haven't even begun to explain which things are wrong.

Rpenner and by the quality of his/her posts should be able to make a distinction between what is wrong and what is right. They claimed nothing was wrong to the extent you have.

And yes, people read my posts. Just letting everyone know what you are up to, before any more back-tracking is observed. Comprende?

You realize that no one is paying any attention to you? Especially after your fiasco with your "Black hole" essay.....

Tach, you remember the other day when you gave me the link for Pauli's book? Within maybe fifteen. Inutes of that pots I did a Google search to locate the other article and one of the top, I think it was four hits was a link to your post. That leads to this thread. You never know how long anything on these forums will last or who may wind up running into them.

When you edit for more than spelling, you should note the reason for the edit.

When you edit for more than spelling, you should note the reason for the edit.

Seoncded. His habit of doing that has been annoying me no end.

Seoncded. His habit of doing that has been annoying me no end.

Thirded. I hate it when someone deletes a post and gives no reason!!! I find it dishonest and distasteful!

Tach, you remember the other day when you gave me the link for Pauli's book? Within maybe fifteen. Inutes of that pots I did a Google search to locate the other article and one of the top, I think it was four hits was a link to your post. That leads to this thread. You never know how long anything on these forums will last or who may wind up running into them.

When you edit for more than spelling, you should note the reason for the edit.

And all these days you couldn't find the time to go to your local library and get the book? Or ask them to get you a copy of the paper for 1$? Thirded. I hate it when someone deletes a post and gives no reason!!! I find it dishonest and distasteful! You mean like the way you quietly edited all the errors I pointed out in your "Black Hole" fiasco? You still missed quite a few. The errors alluded by rpenner are a lot harder , if not impossible, to cover up. And all these days you couldn't find the time to go to your local library and get the book? Or ask them to get you a copy of the paper for 1$?

I told you I put them on my list, but I have six actual paper books I am working on and a boat load of papers, which I admit some take me awhile to really get through.

I'm retired, I got no dead lines and I like to travel when I can. I am in no hurry. Besides if it is really an important question I can ask here or on Physics Forums and someone will help out.

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You mean like the way you quietly edited all the errors I pointed out in your "Black Hole" fiasco?
The errors alluded by rpenner are a lot harder , if not impossible, to cover up.

What edits? Are you accusing me of something?

I told you I noticed ''maybe'' what you where going on about. I made a post each and every time I purported to changing something.

Is there not a system which can check this? I don't like being accused of something which holds NO TRUTH.

I told you I put them on my list, but I have six actual paper books I am working on and a boat load of papers, which I admit some take me awhile to really get through.

I'm retired, I got no dead lines and I like to travel when I can. I am in no hurry. Besides if it is really an important question I can ask here or on Physics Forums and someone will help out.

So, why are you wasting your time trolling this thread? You have quite a bit of catching up to do.