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The Differences Between Tensile Strength, Working Load & Rope Tension

The Differences Between Tensile Strength, Working Load & Rope Tension

When it comes to choosing the right rope for the job, it helps to know what variables are at play, like working load, rope tension, and tensile strength of rope. But exactly what is working load, what is tensile strength, and why does rope tension matter? Keep reading to find out!

What is Tension and Why Does It Matter?

Tension is the pulling force acting along a stretched, flexible connector like a Rope. If you want to hang, pull, swing, or support an object with a rope, you must first create enough tension in the rope to the point where the rope is pulled tight enough to cause the object to move. This tension created by the pulling of the rope in the opposite direction of the object you’re trying to move is called tension force.

If you were to try and push the object with a rope, you would be creating rope slack, and the object would not go anywhere.

How to Find Tension in a Rope

When a rope supports an object’s resting weight, the rope’s tension is equivalent to the object’s weight. The simplest way to determine the tension in a rope is using the following formula:

Tension (T) = the mass of the object (m) x gravitational force (g) plus/minus the mass of the object (m) x acceleration (a).  OR, T= mg + ma.

So, to find the tension in a rope, you will need to determine:

m= mass of the object (kg)

g= gravitational force (9.8 m/s2)

a = acceleration (m/s2)

It’s important to note that rope tension can change based on several variables, and the example above is a simple breakdown of how to find the tension of a non-moving object being pulled straight and not at an angle.

What is Tensile Strength?

Simply put, tensile strength is the resistance of a material to breaking under tension. In other words, tensile strength is the stress in which a rope can take before breaking or failing. Another common name for the tensile strength of rope is breaking strength.

The tensile strength of a rope can vary based on the thickness, material, and style (braided vs. twisted). Also, Knots that are tied into the rope can affect tensile strength. For instance, a ⅜” thick Double Braid Nylon Dockline boasts a tensile strength of 4,200 pounds, while the same dockline in a ½” thickness can support 7,400 pounds before breaking.

It’s important to recognize that the maximum tensile strength of a rope is not the same weight you should be applying to said rope while expecting it to perform safely. For this, you should limit the weight you plan to support based on the rope’s working load.

man walking on slack line to test the tensile strength of rope

What is Working Load?

Working load is the amount of weight a rope can safely support without fear of breaking. As previously mentioned, working load is always going to be less weight than tensile strength weight. In fact, most ropes have a working load between 15 to 25% of the rope’s tensile strength. Working load and tensile strength will change based on whether or not you have knots. If you are wondering whether your rope product has an adequate working load to support your needs, contact the manufacturer directly.

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