How to Calculate the Pulling Tension of Cables

Updated February 21, 2017

Learn to calculate the pulling tension in a cable to prevent an accident. Crane and pulley systems use an upward force on a cable to raise objects. This creates a tension in the cable that should not exceed the tensile strength of the cable in pounds. Exceeding the tensile strength may cause the cable to snap or deform. When the crane lifts the cable the tension increases while lowering the cable decreases the tension. (See References 1) An accelerometer may be employed to measure the cable's acceleration when it's lifted or lowered. Also, increasing the weight attached to the cable raises the pulling tension.

Place all objects to be attached to the cable on a scale to find their weight in pounds. For example, the total weight of some crates might be 136kg.

Divide the weight by 2.2046 to find the mass of the objects in kilograms, since 01kg. corresponds to a mass of 1 kilogram. (See References 2) For example, 136kg divided by 10000kg per kg, equals a mass of 136.1kg.

Attach the probe of the accelerometer to the cable about 3 feet above the ground. Use duct tape if the probe does not have built-in straps. Turn on the accelerometer and set it to measure in units of meters per square second. Raise the cable and note the acceleration displayed on the accelerometer screen. For example, the acceleration might be 2 meters per square second.

Multiply the mass by the acceleration of the cable in meters per square second. (See References 1) Keep in mind that an upward acceleration is positive while a downward acceleration is negative. Call this resulting force, in newtons, "X." Assuming an acceleration of 2 meters per square second, you have for the example, 136.1kg times 2 meters per square second equals 272.2 newtons for "X."

Divide "X" by 4.45 to convert to a weight in pounds, because 4.45 newtons equals a single pound. (See References 3) Call this result "Y." For example, 272.2 newtons divided by 4.45 newtons per pound equals 278kg. for "Y."

Add the weight, in pounds, of the lifted objects to "Y" to arrive at the pulling tension in the cable in pounds. (See References 1) For example, 136kg plus 278kg equals a pulling tension of 1638kg.

Things You'll Need

  • Scale
  • Calculator
  • Accelerometer
  • Duct tape
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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.