Tension force: definition, formula and examples on a day-to-day basis

Tension force: definition, formula and examples on a day-to-day basis

Tension force generally refers to the force exerted on an object, such as a rope, chain, or cable, when it is subjected to an external force that tries to stretch or strain it by trying to separate the molecules that hold it together.

This tension force acts in the opposite direction to the applied force to keep the object in equilibrium.

The magnitude of the tension force depends on the material and geometry of the object, as well as the applied external force. For an ideally inextensible string or cable, the tension force at any point along its length is the same.

If, for example, you have a horizontal rope attached at both ends and you hang an object in the middle, the force of tension in the rope will be equal at both ends and at the point where the object is hung.

Tension force formula

In the case of an ideally inextensible string, the tension force (T) can be calculated using the following formula:

T = F / cos(θ)


  • T = Tension force in the rope.

  • F = External force applied on the rope.

  • θ = Angle between the rope and the direction of the external force (angle of inclination of the rope).

This formula is valid for ideal situations, where the string is inextensible and there are no additional considerations such as friction or elasticity of the material.

In more complex situations, the determination of the tension force may require more detailed analysis and consideration of other factors and laws such as Hooke's law for elastic materials.

Examples of tension forces

The forces of tension are found in numerous contexts in our daily lives. Here are some examples where you can observe these types of forces:

  1. Ropes and Cables: When you pull on a rope or cable, whether to lift an object, close a door, or tow a vehicle, you are applying a tension force to the rope or cable.

  2. Suspension Bridge: Suspension bridges use cables to support their platform. The cables are subjected to tension forces that act to support the weight of the platform and the vehicles that cross the bridge.

  3. Steel rebar reinforced concrete is an ingenious combination that takes advantage of steel's ability to resist tensile stresses to compensate for the low tensile strength of concrete. In contrast, concrete has excellent compressive strength.

  4. Elevator: In an elevator, the cable that supports the car and allows movement up and down is subjected to tension forces to support the weight of the passengers and the car itself.

  5. Power Transmission Lines: Overhead power lines that carry power from power plants to homes and businesses are made up of cables subjected to tension forces to support the weight of the cable and electrical conductors.

  6. Kites: When you fly a kite, the string that supports the kite is under tension, allowing the kite to stay aloft.

  7. Parachutes: Parachutes used for the controlled descent of people or equipment also rely on the tension in their cords to deploy and remain stable during the descent.

  8. Ship Moorings: Docked ships use ropes or ropes called mooring lines to stay attached to the pier, and these mooring lines are subjected to tension forces due to waves and currents.

Use and applications of tension forces

The force of tension is important for several fundamental reasons in physics and in our daily lives:

  1. Stability and balance : The tension force is essential to maintain the stability and balance of structures and objects. For example, on a suspension bridge, the tension force in the cables allows the bridge deck to remain suspended and can support the weight of crossing vehicles.

  2. Lifting and pulling : Tension force is used to lift objects or apply pulling force in a variety of situations, from lifting a lift to towing a disabled vehicle.

  3. Engineering safety : In many designs and constructions, the tension force is a crucial aspect to consider. Ensuring that the materials used can withstand the expected tension forces is essential to prevent structural failure and ensure the safety of people.

  4. Sports and recreation : In sports and recreational activities, the tension force plays an important role. For example, in the use of ropes in climbing, parachuting, kiting or archery, tension is necessary for these activities to work correctly and safely.

  5. Transmission of forces : In many mechanical devices, the force of tension is used to transmit forces between components. For example, in pulleys, the ropes or belts transmit the necessary tension force to move objects or machinery.

  6. Electricity and communication : In power lines and communication cables, the tenson force is crucial to keep the cables in place and ensure the effective transmission of electricity or data.

  7. Scientific experiments : In scientific research and experimentation, the tension force is used to measure and understand material properties, evaluate the resistance of structures, and determine physical behavior.

Tension force measurement

Tension force is measured directly through the application of suitable measuring devices or instruments that can capture the magnitude of the force exerted on a rope, cable, or material that is under tension.

There are different types of devices and techniques to measure the tension force, and the choice depends on the context and the type of object or material being evaluated. Some common methods for measuring tension strength include:

  • Dynamometers : Dynamometers are portable devices that measure tension and compression forces. They can be used to measure the tension force in ropes, cables, or items under tension.

  • Load cells : They are sensors that measure the force applied in a specific direction. They are used in a wide variety of applications, such as weighing objects, measuring force on industrial machines, or stressing on structures.

  • Extensometers : These devices measure the deformation of a material under stress and convert it into a measure of the applied force. They are commonly used in testing materials to assess their mechanical properties.

  • Testing machines : To evaluate the mechanical properties of materials, testing machines are used that apply controlled forces and measure the response of the material under stress.

  • Load Tests: In construction and civil engineering, load tests are performed on structures to measure their ability to withstand tension and compression forces.

Difference with surface tension strength

This concept should not be confused with that of surface tension.

The surface tension force refers to the force that acts on the surface of a liquid and tends to decrease its surface area to the minimum possible. It is a physical property that is due to the cohesive forces between the molecules of the liquid.

At a free surface of the liquid, such as at the interface between the liquid and the air, the molecules inside the liquid are drawn inward due to cohesive forces, resulting in a kind of "skin" on the surface. .

Surface tension is responsible for some interesting phenomena, such as the formation of spherical bubbles and droplets, since a spherical shape minimizes the surface area and therefore minimizes the energy of the liquid surface.

Publication Date: July 31, 2023
Last Revision: July 31, 2023