How odometer works in physics ?

[haleh]

How odometer works in physics ??

I get a problem ,my university professor for physics 1 ask me to search about work of odometer in physical view ,I mean he doesn't want to describe the mechanical or electronic odometers !he wants me to write physical formulas and measure the distance which cars travel the same as what odometer does !and it should be at least 4 page . I some how search and I understand that electronic or mechanical ones measure the rpm of wheels and then convert this to kilometer or mile and this can be like this : number of revolution * radius of wheel * 2 * pi
but I some how confused that rpm is not number of revolution ,Is there any timer in cars? or maybe I am completely wrong and my professor wants other things so what do you suggest me to search about ?and is there any link ,book you can suggest me ? any idea ??

 

[rcgldr]

Mechanical odometers are just geared so that rotation of the tires results in advancement of the odometer based on the assumed radius of the tire. The input could be from somewhere in the drivetrain or from one of the axles of the non-driven wheels (like a bicycle's odometer / speedometer driven by a gear attached to the front wheel axle).

Electronic odometers may use drivetrain related data, such as engine rpm plus what gear the car is in (as well as the expected tire radius).

Wiki articles:

http://en.wikipedia.org/wiki/Odometer

http://en.wikipedia.org/wiki/Speedometer