How to Determine Tension in Pulleys

Pulleys are used in a vast variety of lifting tasks, from small-scale household lifting to much larger pulleys used in industrial elevators and large-scale construction projects. The pulley is one of the most basic simple machines referred to in physics, along with the first- and second-degree levers and the wheel and axle. The way to determine the tension in a pulley is extremely simple, and is based on the same simple physical properties that make it so effective as a labor-saving device. The calculations will vary slightly from one pulley to another, but the principle remains the same.

Instructions

1. Calculate the weight on the end of the pulley (the object that the pulley is being used to lift). Perform this measurement in whichever way you choose if you do not have the information already available.

2. Count the number of wheels in the pulley, both on the top and at the bottom, which will also give you the number of strings (or ropes or cables, etc.) that are supporting the weight being lifted.

3. Divide the weight of the object being lifted by the number of wheels or supporting cables. If you are lifting a 100-lb. weight with a five-wheel pulley, for example, the tension will be 20 lbs. (100/5=20)

References

• Pulley basics
• Summerlift: Physics of pulleys