This is just a question that has been bothering me. I am not a student of physics, which is probably clear from my question. Hope it at least makes sense: You have a windmill with no friction. The wind is blowing at a constant speed causing the windmill to spin at 100 RPM.(a) The windmill is hooked up to a pulley with no friction with a 1 kg weight attached. The energy transfer from the wind to the windmill to the pulley occurs with 100% efficiency. Now that the weight is attached, enough constant force is exerted by the wind on the windmill to raise the weight 1 m / sec. (1 joule of work) What happens? Does the windmill slow down because of the weight? Seems like if the weight was attached while the windmill was already spinning, 100% of the force of the wind would be transferred to the pulley. But the windmill would just keep spinning anyway since there's no friction. But if the windmill started out at rest when you hooked up the pulley, I don't know what would happen. Would it take longer to lift the weight since the force of the wind is being used for both purposes, lifting the weight and accelerating the windmill blades? So is the weight raised at 0.5 m/ sec until the windmill gets up to 100 RPM, and then start going up at 1m / sec? Or something like that? (a) If the windmill has no friction, then it would spin perpetually at 100 RPM from a single gust. So I guess the amount of power exerted by that first gust to get the windmill from rest to a speed of 100RPM is all that matters. After that, the windmill would just spin at the same rate whether the wind continues to blow or not???