Monday, 22 October 2018

newtonian mechanics - Work done by static friction on a car


The tires of a car execute pure rolling. Therefore, the work done by friction on the tires (and hence the car) is zero. If no external work is done, how does a car's kinetic energy increase?



Answer



The increase in the car's kinetic energy comes from the internal energy of the car, stored, for example, in its gasoline or batteries.


The engine exerts torque over the wheels, which are prevented by the friction from simply rotating in place. The reaction from the ground on the car (wheels) makes it move faster.


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