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Re: [Phys-L] [SPAM] Re: The Make-Believe World of Real World Physics

On 7/30/2013 6:01 PM, jbellina wrote:
No I don't think so, if it is digital is has to acquire for something more than an infinitesmal time. I'll have to think about the analog one.

joe

On Jul 30, 2013, at 6:32 PM, Bernard Cleyet wrote:

Does not a speedometer give "instantaneous" speed.
Joseph J. Bellina, Jr. Ph.D.
Emeritus Professor of Physics
Co-Director
Northern Indiana Science, Mathematics, and Engineering Collaborative
574-276-8294
inquirybellina@comcast.net

One way of providing electrical transmission from vehicle speed sensors is via a pulse generator tied to the final shaft of the transmission. This leads to Joe's reasonable (implied) assertion that speed changes occurring at much shorter time intervals than the pulse repetition period , would not be transmitted. The classical analog method featured a flexible cable drive from the final shaft up to the speedo head where it spun a magnet wheel dragging a spring-return aluminum disk attached to the pointer by induced eddy currents.
Here the least significant period for indication is more difficult to conceive: the mechanical speedo transmission has a limiting upper frequency, like any transmission line does - but it would be rather high and heavily filtered by design.
The design principle in question is to provide a very low upper frequency cutoff for instruments to avoid road vibration induced resonances: the prime example is the fuel gauge, which may take ten seconds or more to register a step increase in fuel level.

Brian Whatcott Altus OK