How to Calculate the Tensile Force on a Cable System

Updated February 21, 2017

Consider calculating the tensile force, also called tension, on a cable system to avoid an accident. Weights hung from a cable or rope produce a tensile force which should not exceed the tension rating of the cable. If the tension rating is passed the cable may snap, causing injury or property damage. The tension in the cable depends on the weight hanging from it and the acceleration of the cable. A downward accelerating cable reduces tension, but an upward acceleration increases tension. Forces and weights are measured in newtons in science and in pounds in standard units.

Change the weight of the hanging object from pounds into newtons by dividing by 0.2248, because each newton contains 0.102kg. As an example, assume a 227kg. cable hangs from the cable. The weight in newtons is then 2268kg. divided by 1020kg. per newton, or 2,224.2 newtons.

Convert the weight of the hanging object into a mass in kilograms by dividing by 2.2046, since a kilogram contains 10000kg. Performing this step, you have 2268kg. divided by 10000kg. per kg, or a mass of 226.8kg.

Multiply the mass by the cable acceleration in meters per second squared. Call this result "X." Continuing the exercise yields 226.8kg times 0.5 meters per second squared, or 113.4 newtons.

Add "X" to the weight, in newtons, if the cable is moving upward, to arrive at the tensile force in the cable in newtons. Subtract "X" from the weight, in newtons, if the cable is moving downward to arrive at the tensile force in the cable in newtons. Completing this step leads to 2,224.2 newtons plus 113.4 newtons, or a tensile force of 2,337.6 newtons.

Convert the tensile force to pounds, if desired. Performing this step leads to 2,337.6 newtons multiplied by 1020kg. per newton, or 2384kg.


Use metric units when performing a tension calculation to get the right result. A newton is the scientific unit of force equal to a kilogram times meters per second squared.

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About the Author

William Hirsch started writing during graduate school in 2005. His work has been published in the scientific journal "Physical Review Letters." He specializes in computer-related and physical science articles. Hirsch holds a Ph.D. from Wake Forest University in theoretical physics, where he studied particle physics and black holes.