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 ??