Old Apr 27, 2005 | 01:33 PM
  #141 (permalink)  
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power2weight
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To answer your question, I think it's best to describe the car as a free body floating in space. We engineers have been taught to think of objects as free-bodies in space with mass acted on by forces with a net value on the various linear and rotational axes. When a force acts through the center of a body of mass, like a pool ball, it causes linear motion. When it acts upon a body of mass such that the force vector does not pass through the center of mass, rotation and motion occur.

A simple free body diagram for a car could look like this:


In the 'Y' direction we have the center of mass (CM), and the 2 reaction (R) forces at play at the tires. Sum the reaction forces and it will equal the weight of the car. Multiply these reaction forces by the coefficient of friction and you have the maximum available force for acceleration.

Once we rotate the drive axles, the diameter of the drive tires from the axle to contact patch on the pavement (a lever-arm on a rolling object) can be factored in to determine the force which pushes backwards at the track (F1 to the left) in order to propel the car forward (F1 to the right).

Sooner or later, all the complex factors involved here, the interaction of the chaisis to the suspension to the drive axel's, the deflection of the tire's sidewall, the aerodynamic drag, the friction of mechanical parts sliding against each other on hydrodynamic oil films, etc all could be sumed to resultant vectors about the 6 axis's (XYZ, and rotation with respect to those axis's) and ultimatly applied to the center of mass.
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