Pete Plumb
R.I.P.
The other day while looking for a new car, I got the standard lecture from the salesman about "how much torque this thing has". I tried to explain that, by definition, torque and horsepower are intimately connected. I guess the guy had a spark of engineering spirit in him because he asked me to explain that. I drew this simple little diagram out for him and thought I might pass it along in case some of you here were wondering the same thing.
EXPLANATION: "One horsepower" is defined as "The amount of energy it takes to move 550 pounds one foot in one second". The diagram shows a 550 lb block being lifted of the ground 12" by a rope, passing over a pulley and to a shaft, whose diameter is such that 1 revolution of the shaft is exactly 12" (12 divided by 3.1416) or 3.8197" in diameter. This shaft has a radius of 1.9098" which is the lever arm with which to lift the weight. So, 1.9098" x 550 lbs = 1050.39 in-lbs. Since the salesman was bantering around "ft-lbs", I said, "Okay, 1050.39 in-lbs divided by 12" = 87.5325 ft-lbs. Now, since we speak in terms of Revs Per Minute, 87.5325 x 60 seconds = 5251.95 ft-lbs per minute. I had to round a few numbers to get it to 5252 but, the point is, he GOT it and thanked me for explaining it because he "had always wondered how that worked". Whether he can explain it to the next guy that walks in the door is another story.
EXPLANATION: "One horsepower" is defined as "The amount of energy it takes to move 550 pounds one foot in one second". The diagram shows a 550 lb block being lifted of the ground 12" by a rope, passing over a pulley and to a shaft, whose diameter is such that 1 revolution of the shaft is exactly 12" (12 divided by 3.1416) or 3.8197" in diameter. This shaft has a radius of 1.9098" which is the lever arm with which to lift the weight. So, 1.9098" x 550 lbs = 1050.39 in-lbs. Since the salesman was bantering around "ft-lbs", I said, "Okay, 1050.39 in-lbs divided by 12" = 87.5325 ft-lbs. Now, since we speak in terms of Revs Per Minute, 87.5325 x 60 seconds = 5251.95 ft-lbs per minute. I had to round a few numbers to get it to 5252 but, the point is, he GOT it and thanked me for explaining it because he "had always wondered how that worked". Whether he can explain it to the next guy that walks in the door is another story.
