I work in a factory that makes boxes. I do tests for the engineers
that design the boxes. One day they came to me and said they wanted me
to test this box made out of a new material. They told me to load it
down until it took 55 pounds of force to pull it across the floor at 10
feet per second. So I attached a spring gage to it and started loading
and pulling until I got what they wanted. They said they wanted it
pulled around for ten minutes. I got to tell you, it didn’t take any
time at all until I was worn out!

I went back to them and asked them if
there was some way I could rig up a motor to do the same. One of the
engineers looked at the test and said that I could rig up a motor to
pull it around in a 38” diameter circle on the end of an arm at 60 rpm,
but I‘d need at least a one horsepower motor to do the job. I asked him
how he knew that and he said “Simple, 55 pounds times ten feet per
second divided by 550 equals one horsepower. So a 38” diameter circle
has a circumference of 10 feet, and if it rotates at 60 rpm, or one
revolution per second, it will travel ten feet per second” Wow! I was
impressed! But then I asked him how much torque would it take, and he
said it would be 55 pounds times the diameter over two or 1045
inch-pounds or 87 foot-pounds. So I got me a motor and geared it so it
would move that box around that circle at 60 rpm and he got his test.

I
said to him that it seems there must be some relation between torque and
power and he told me that if I took the torque and multiplied it by the
rpm and divided that by 5252 it would give me the horsepower. So I tried
it and sure enough, it came out to one horsepower just like he figured
it before! I said that was bloody marvelous, and so he said to me, “Say
you have a motor rated at 100 horsepower at 5252 rpm. Well, you can get
100 foot-pounds of torque out of it at that speed, or you can gear it
down to 2626 rpm and get 200 foot-pounds, or gear it down to 1313 rpm
and get 400 foot-pounds of torque.” I got to tell you, I look at
horsepower and torque in a new way now!

Paul Lipps

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