Background of Physics and Torque

Written by Craig Fry and Paul Grosse   
Saturday, 10 July 2004

Explanation of Torque

Reprinted by permission of Craig Fry, from http://home.fuse.net/pagrosse/

Torque

Torque is strength; horsepower is speed. Torque is a measure of how much weight you can move; horsepower is a measure of how fast you can move a specific weight. For example, human weightlifting contests are contests of torque. Each competitor must lift the same amount of weight and the guy who can lift the most is the guy who has the most torque. If weightlifting contests were contests of horsepower then the winner would be the guy who can get a specific weight over his head the fastest.

If you have a one pound weight bolted to the floor, and try to lift it with one pound of force (or any other weight), you will have applied force and exerted energy, but no work will have been done. If you unbolt the weight, and apply a force sufficient to lift the weight one-foot, then one foot pound of work will have been done. If that event takes a minute to accomplish, then you will be doing work at the rate of one foot pound per minute. If it takes one second to accomplish the task, then work will be done at the rate of 60 foot pounds per minute, you get the idea.

In order to apply these measurements to automobiles and their performance (whether you're speaking of torque, horsepower, or Newton meters), you need to address the three variables of force, work and time.

A gentleman by the name of Watt made some observations, and concluded that the average horse of the time could lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 foot pounds per second.  This is 33,000 foot pounds per minute, for an eight hour shift, more or less. He then published those observations, and stated that 33,000 foot pounds per minute of work was equivalent to the power of one horse, or, one horsepower.

We need to measure units of force from rotating objects such as crankshafts, so we'll use terms which define a twisting or turning force, such as foot pounds of torque. A foot pound of torque is the twisting force necessary to support a one pound weight on a weightless horizontal bar, one foot from the fulcrum or the center pivot point.

Now, it's important to understand that nobody on the planet ever actually measures horsepower from a running engine. What we actually measure is torque, expressed in foot-pounds.  This information can be obtained on a dynamometer. Then the actual horsepower is computed by converting the twisting force of torque into the work units of horsepower.

Now take that one pound weight we mentioned before. If we rotate that weight for one full revolution against a one pound resistance, we have moved it a total of 6.2832 feet (Pi * a two foot circle), and, incidentally, we have done 6.2832 foot pounds of work.  Now Watt said that 33,000 foot pounds of work per minute was equivalent to one horsepower. If we divide the 6.2832 foot pounds of work we have done per revolution of that weight into 33,000 foot pounds, we come up with the fact that one foot pound of torque at 5252 rpm is equal to 33,000 foot pounds per minute of work, and is the equivalent of one horsepower. If we only move that weight at the rate of 2626 rpm, it's the equivalent of 1/2 horsepower (16,500 foot pounds per minute), and so on. Therefore, the following formula applies for calculating horsepower from a torque measurement:

                                     Torque * RPM
        Horsepower      =      -----------------
                                                 5252
 
 
 

"Encyclpaedia Britannica." Torque. http://search.britannica.com/bcom/eb/article/idxref/1/0,5716,110227,00.html

Beer, Ferdinand P., Johnston, E. Russell Jr. Mechanics of Materials. New York: McGraw-Hill, Inc., 1981.



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DISCLAIMER: This information and procedure is provided as a courtesy and is for informational purposes only.  Neither the publishers nor the authors accept any responsibility for the accuracy, applicability, or suitability of this procedure.  You assume all risks associated with the use of this information.  NEITHER THE PUBLISHERs NOR THE AUTHORs SHALL IN ANY EVENT BE LIABLE FOR ANY DIRECT, INDIRECT, PUNITIVE, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, OF ANY NATURE ARISING OUT OF OR IN ANY WAY CONNECTED WITH THE USE OR MISUSE OF THIS INFORMATION OR LACK OF INFORMATION.  Any type of modification or service work on your motorcycle should always be performed by a professional mechanic. If performed incorrectly, this procedure may endanger the safety of you and others on your motorcycle and possibly invalidate your manufacturer’s warranty.


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  Comments (1)
roadstar 1700
Written by GLEN, on 10-08-2006 21:34
Can anyone tell me the horse power this bike has?

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