When you are calculating the amount of mechanical energy used to exert force and move something, you are talking about work being done by a force at a distance. You can describe this in terms of foot-pounds. For example, you want to calculate the energy used to tighten a nut when using a wrench, or to lift a weight from the floor. Mechanical force takes place in time, so to describe the power requirement, you use foot-pounds per second.
Type into a calculator the number in feet for the distance from the center of the force being applied, such as a nut that needs tightening, and length at which the force is being applied, such as the end of a 1-foot-long wrench.
Press the “Multiply” key on the calculator.
Type in the number representing the amount of force that you must apply to the wrench in order to turn the nut, such as 200 pounds of force.
Press the “Equal” key to get the answer of 200 foot-pounds (1 foot of distance times 200 pounds of force exerted).
Press the “Divide” key and then type in the number representing how much time it took to do the work, such as five seconds. If it took you five seconds to move the wrench, you were working with 200 foot-pounds divided by five seconds, or 40 foot-pounds per second.
Weigh and object, such as a 2-pound weight, and multiply it by the number of feet you lift it off of the ground, such as 3 feet, to calculate that you used 6 foot-pounds of energy. If you took two seconds to lift the weight, you used 3 foot-pounds per second.
About the Author
Julius Vandersteen has been a freelance writer since 1999. His work has appeared in “The Los Angeles Times,” “Wired” and “S.F. Weekly.” Vandersteen has a Bachelor of Arts in journalism from San Francisco State University.