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Thread: My Simple-minded Horsepower

  1. #1 My Simple-minded Horsepower 
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    If you as a student, or novice interested in things mechanical, like I, have difficulty understanding the way horsepower and rotating machines are interrelated, look at my simple-minded diagram below. A drum with radius r=3 ft. is rotating at a constant speed of 500 rpm, raising a cable-suspended 100 lb. weight W by winding the cable up on the drum. The circumference of the drum is obviously (pi) X (diameter), or (pi) X (2r), which is (pi) X 6= 18.85 ft. Therefore, 18.85 ft. of cable are wound onto the drum each time it makes one revolution, this also raising the weight 18.85 ft.

    Since the drum is turning at 500 rpm, it raises the weight 500 X 18.85 ft. in a minute, or 9425 ft. per minute. From the familiar formula for work done, Work = Force X Distance, Work Done each minute is 100 lbs. (the weight being raised) X 9425, or 942,500 ft.- lbs. Knowing that 33,000 ft.-lbs. of work done in a minute represent 1 Horsepower, the drum is expending 942,500 divided by 33,000, or 24.2 HP.

    We can move these quantities around to form a formula for HP relating the rotational speed and torque being applied, to get this: HP = 2(pi) X rpm X torque divided by 33,000. Using this with the numbers for the drum example:

    HP = 6.28 X 500 X 300 divided by 33,000, and get 28.5 HP, noting the TORQUE is the lever-arm (radius of drum) X WEIGHT.

    So, if you have an automobile engine for example running at 2000 rpm, and know it is developing 150 ft. -lbs. of torque, it's horsepower being expended is 6.28 X 2000 X 150 / 33,000 = 57.1 HP. Hope you can excuse my horrible editing on the drawing! jocular

    Edit: Please note on the drawing, I left off the fact that 1 HP = 33,000 Ft.-lbs. PER MINUTE






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    Forum Ph.D. merumario's Avatar
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    i wonder the major aim of your threads!


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  4. #3  
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    Quote Originally Posted by merumario View Post
    i wonder the major aim of your threads!
    All of them? jocular
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    Life-Size Nanoputian Flick Montana's Avatar
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    Quote Originally Posted by merumario View Post
    i wonder the major aim of your threads!
    World domination. Clearly.
    "Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us." -Calvin
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    Malignant Pimple shlunka's Avatar
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    Your horse drawing is terrible. I suggest you buy a horse model to go off of next time.
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  7. #6  
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    Quote Originally Posted by shlunka View Post
    Your horse drawing is terrible. I suggest you buy a horse model to go off of next time.
    Yeah, I guess yer all right, the thread is pretty H. S. jocular



    Edit: Sometimes ya can't win around here, some "like", some "don't like". Keeps the world a merry place!
    Last edited by jocular; July 29th, 2013 at 06:26 PM.
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    It looks like you made a correction to the hp on the drawing but forgot to fix the text.
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  9. #8  
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    Quote Originally Posted by jocular View Post
    Sometimes ya can't win around here, some "like", some "don't like". Keeps the world a merry place!
    It's the way of the world- No one can please everyone.
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  10. #9  
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    Quote Originally Posted by Harold14370 View Post
    It looks like you made a correction to the hp on the drawing but forgot to fix the text.
    At this point, bewildered, and perplexed, I concede the thought that perhaps created gremlins unanticipated. For some unexplainable reason, making the drawing, my old faculties kept hammering at, 39,000 ft lbs/ min, then I remembered, tried "edit", a new function for me, got all squiggly, thought of the "omsquig" portico, and that was it!

    Horsepower was never a totally understood concept, for me, and the analogy of doing work per unit time clarified it, but too late for finals! Some feel my thoughts are incongruous, as does the party in Nigeria. Thus, I thought a simple comparison might make a "mental connection", for those in similar straits to mine as a student, long ago.

    My gut feel by now is, Ahhh, fuck it all. jocular
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