The energy output of an engine is not constant; it varies with changes in torque and RPM. The formula for power, given by (rpm * torque) / 9.54, indicates that pressing the gas pedal increases both RPM and torque, thereby increasing power output. Additionally, when comparing running and walking, more energy is expended while running due to higher power output over a shorter time, despite gravity not doing work in the vertical direction. The first law of thermodynamics confirms that increased fuel consumption correlates with higher power output.
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I think the qualifier also implied only losses internal to the engine, so it is true at constant speed as well -- the real world application being what I described above.A.T. said:... to accelerate from zero to a certain speed assuming the same mass.
Some of the losses are a fixed function of size, not a fraction of output. So for identical cars and driving, the smaller engine will essentially always produce better fuel efficiency.Thom_Silva said:So is theoretically possible to have a very powerfull car (a super car for example), that can use less fuel to mantain a given speed than a less powerful car. If that is true, that's an interesting realization. I wonder why doesn't that happen more frequently, if it happens at all.