Re: transfer of momentum/speedos

[Brian Whatcott <betwys1@SBCGLOBAL.NET>]

The return spring on the usual analog speedo is often biassed to hold
the pointer gently against the pin stop.

Accordingly, the range from 0-5 mph is often compressed on the scale.
But minor fluctuations in the eddy current drive which can be
distracting at low forward speeds where there is least return torque
do not cause the pointer to bob about so noticeably.

 The speedo cable of the mechanical type is always connected to the
transmission, so there is a small reverse loading from the stop on the
pointer during reversing.   Because of this mechanical link at the
 drive shaft,  changes in axle ratio or tire/rim size cause speed
indication errors.

Brian W

At 01:51 PM 11/19/2003, you wrote:
> My guess is that analog speedometers are disconnected
> from the axle when the transmission is in reverse.
>
> Daniel Crowe
> Oklahoma School of Science and Mathematics
> Ardmore Regional Center
> dcrowe@sotc.org
>
>
> -----Original Message-----
> =46rom: Bernard Cleyet [mailto:anngeorg@PACBELL.NET]
> Sent: Wednesday, November 19, 2003 1:36 PM
> To: PHYS-L@lists.nau.edu
> Subject: Re: transfer of momentum
>
>
> If one removes the pin, it might read below the zero.  Same w/
> d'Arsonval meters (usually no pin.)
>
> bc
>
>
>
> Hugh Haskell wrote:
>
> >At 12:58 -0500 11/19/03, Joseph Bellina wrote:
> >
> >
> >
> >>Here speed is what the car speedometer reads.
> >>
> >>
> >
> >And if it's an analog speedometer, when backing up it always reads
> >zero. But your statement is true for digital speedometers.


Brian Whatcott    Altus OK    Eureka!