Re:speedo accuracy - NAC

["Obie Fayth" <bibendum59@domain.elided>]

>Date: Tue, 29 Jan 2002 13:50:51 -0500
>From: Joe Elliott <jee@domain.elided>
>Subject: Re:speedo accuracy
>

>Well, the speedo's electrical systems will still be 100% accurate,
>because both the sender and the gauge will be stationary in your
>reference frame.  As for measuring the accuracy of the gauge at these
>speeds, I think this is where fancy GPS toys come in handy.  If your
>GPS isn't programmed to compensate for the weird stuff that happens
>at slightly subluminal speeds, just have your wife stand on the side
>of the road and measure the length of the car when it goes by at a
>given indicated speed on the speedo.  Your actual speed can be
>determined by the percentage difference in the real length of your
>car and length observed by your wife.  The car will appear shorter by
>a factor of the square root of (1 - B^2) where B is your speed as a
>factor of the speed of light.  So just solve (1 - B^2) = [(observed
>length) / (proper length)]^2 for B and multiply B by the speed of
>light (299,792,458 m/sec last time I checked) and see if it matches
>the speedo.  But you might want to check my math first.  All I know
>for sure is that it's not worth investing in clear taillight lenses
>for your Honda because at those speeds (assuming your Honda has a big
>enough Wal-Mart spoiler to allow it to reach those speeds) they'll
>just appear red to stationary observers and slower traffic anyway,
>due to the Doppler shift of the light waves.

	After Joe's excellent write-up on Doppler shift I finally realized 
something. I used to think that those blue "ion" headlights just had some 
kind of coating on the bulb when in fact they actually make your car so fast 
that when someone sees you approaching the light emitted from your 
headlights shifts towards the blue end of the spectum. Wow! Actual 
scientific evidence you can see with your own eyes. Not bad for a $13 bolt 
on part.
	Now I wonder what those flashing red and blue lights in my rear view mirror 
mean... High speed Oval track racer? Some tricked out Civic with a flux 
capacitor backing up then driving forward over and over again?

-Obie
Tacoma, Wa.
assorted Alfas, no flux capacitors



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