Suppose a car with electrical engine moves uniformly with friction between wheels and the ground (neglect air resistance, energy loss, etc.). So why the car's engine power must be equal to friction's power for the car to move uniformly?
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asked May 19, 2022 at 9:48
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$\begingroup$ Because Newton's second law. No acceleration = no net force $\endgroup$– DKNguyenCommented May 19, 2022 at 13:42
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2 Answers
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If the engine produces more power, that has to go somewhere, and in the situation you describe, it will go into kinetic energy, meaning to accelerate the car.
If it produces less power, the friction will get its missing power from kinetic energy, thus decelerating the car.
Only if the engine power matches the friction power, kinetic energy stays untouched, meaning constant speed.
That matches our everyday experience. There's always one gas pedal position for constant speed. Pushing harder (more engine power) accelerates, pushing less than that decelerates.
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You loos energy by heating the surrounding by friction. Your engine has to produce (at least) that energy every second, and energy=power times time.
