Jeff Root wrote:
> Jim Greenfield replied to Jeff Root:
> >> George Dishman wrote:
> >> > (3) AND (4) ARE QUESTIONS, NOT REASONS.
> >> Actually they're scenarios, which were described in order
> >> to pose and answer the questions.
> > Agree. George is running interference
> I can't even guess what you mean by that remark.
> >> Of course, a scenario doesn't cause Doppler shift, any
> >> more than a question does.
> >> The question is:
> >> What causes the Doppler shift in scenario (3)?
> > Make that question (a)
> > Answer: Change in position at instant of firing
> That's good. Since the position at the instant of
> firing is the only thing that changes, that must be
> what causes the Doppler shift in this scenario.
> > Question (b)
> > What causes the Doppler shift in scenario (4)?
> Good question. I should have included it in my post.
> > Answer: Increased bullet velocity
> Okay, that's interesting. You say that the cause of the
> Doppler shift in scenario (4) is different from the cause
> in scenario (3).
> > .........(for an extra 1/2 mark, the position change
> > is incidental)
> Yes. Scenario (4) has both a change in position and a
> change in speed at the instant of firing.
> Compare the amount of Doppler shift in the scenarios.
> In my animation, the times between bullet hits on the
> targets are:
> 1) 15.0 frames
> 2) 15.0 frames
> 3) 7.5 frames
> 4) 10.0 frames
> So the frequencies are:
> 1) 0.066 per frame
> 2) 0.066 per frame
> 3) 0.133 per frame
> 4) 0.100 per frame
> Cases (1) and (2) have no Doppler shift. Case (3) has
> the most Doppler shift, and case (4) has some Doppler
> shift, but less than case (3).
> Case (4) has exactly the same change in position that
> case (3) has. Shouldn't that change in position cause
> Doppler shift? Since the position changes by the same
> amount in both cases, shouldn't it cause the same amount
> of Doppler shift in both cases?
> Why is the Doppler shift in case (4) less than that in
> case (3)? The only difference between the two cases is
> that case (4) also has an increase in speed. Somehow,
> the increased speed in case (4) caused the amount of
> Doppler shift to be less than it is in case (3).
> > Question (c)
> > Which of the two ACTUALLY caused the Doppler shift, and
> > where is the evidence?
> > Answer: (4), because it demonstrated increased kinetic
> > energy delivered to the target, whereas (3) did not.
> Again, (4) is a scenario, not a cause of Doppler shift.
> Scenarios do not cause Doppler shift. If you mean that
> a change of speed causes Doppler shift, then say so.
> Sticking the word "ACTUALLY" into the sentence doesn't
> accomplish anything. We agree that the Doppler shift in
> case (3) is caused by the change in position. We haven't
> quite figured out yet what is going on in case (4).
> You say that the change in speed in case (4) causes the
> Doppler shift. I point out that, if change in position
> causes Doppler shift in case (3), then it must also cause
> the same amount of Doppler shift in case (4).
> But case (4) has less Doppler shift than case (3), even
> though the only difference between the two is that there
> is an increase in speed in case (4).
> If an increase in speed causes Doppler shift, shouldn't
> there be more Doppler shift in case (4) than in case (3)?
> And if an increase in speed causes Doppler shift, why is
> there no Doppler shift at all in case (2)?
Most covered before, except to comment that your "belief" in the
that it is a true representation of reality. I disagree!
As v=frequency X wavelength, an increase in bullet v = corresponding
increase in frequency, and NO CHANGE indicated for wavelength.
I couldn't be bothered responding more to (3). My original analogy had
gun mounted on an aircraft. To discuss a "scenario" where a plane stops
is nothing short of pathetic.
The reason for the doppler is (4), as presented.
PS: Are you one of these individuals, who because they "saw it" on a
computer animation, is convinced they are looking at reality?
Hint: We are NOT about to be invaided by aliens.