Well folks I hope I don't bore you, I'll try and make his simple to understand. Just a little about me. I have a degree in Physics and have over 30 years as an applications engineer applying variable speed drives to industrial machines. I have expierience with everything from small 1/10th HP all the way up to 10,000 HP.
First a fiew principles to understand.
HP is the ability to do work over time. The definition of HP is 1 HP is the ability to lift 33000 lbs 1 foot in 1 minute. When applied to rotary motion then HP = (torque x RPM)/k. The K is 63025 if we are working with in.lbs torque and 5252 if we are working with ft.lbs. So working backwards 1 HP x63025/1750RPMs would mean we would get 36 in.lbs of torque. 1 hp x875/63025=72 in. lbs. That is exactly how a step pulley or a reeves drive works. As the speed goes down then the torque goes up accordingly and vice a vesa.