I understand that the engine delivers power to the wheels and friction from the ground causes the wheels to roll. However, given the power (work per time) at the wheels, how does that energy become the kinetic energy of the car, since friction force from road doesn't do any work?
Is it simply becuase the wheels roll causing internal forces at the axle/frame/body of car to do work speeding the car up therefore gaining kinetic energy?
I'm assuming we ignore friction, air resistance and it's a flat road
Best Answer
This is something I've seen several times on this site lately, and I disagree with it.
Static friction does do net translational work on the car. It applies a force in the direction of displacement; work is being done on the car due to the static friction force. I cannot see any way around this with the definition of work.
The engine (through the transmission) does work on the wheels. This is what causes them to spin. The spinning wheels are now able to do work against the road, and the road provides a nearly equal and opposite work back, with some losses. Since we are talking about the work done on the car, not on the car+road system, we can see that when you isolate the forces acting on the car, the static friction absolutely does work by the traditional definitions. It is providing a force in the direction of motion.
If we ignore friction (like your question mentions), the road obviously cannot do work on the car, and all the power from the engine just goes into rotational work of the wheels. You need the wheels to be coupled to the road by friction to actually get any translational work/kinetic energy from this rotation. This is how the static friction does work on the car.