Task: Sentence Expansion
Input (English): When this is the case , traction is often expressed as the ratio of the maximum tractive force to the normal force and is termed the " coefficient of traction " ( similar to coefficient of friction ) .
Output (English): Traction can also refer to the " maximum " tractive force between a body and a surface , as limited by available friction ; when this is the case , traction is often expressed as the ratio of the maximum tractive force to the normal force and is termed the " coefficient of traction " ( similar to coefficient of friction ) .