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Tension
Beginner
Pulling force transmitted along a rope or string.
Tension is the pulling force transmitted through a rope or string. For a light, inextensible rope over a smooth pulley the tension is the same everywhere along it. It pulls on whatever the rope is attached to.
A 3 kg mass hung at rest has T = 29.4 N.
Tension changes if the rope has mass or rubs a rough pulley.
In more detail
Tension is the pulling force transmitted through a rope, string or cable. For an ideal light rope, the tension is the same throughout its length.
Real-world uses
- Cable-stayed bridges rely on tension in their stays.
- Lifting cranes use tension in cables to hoist loads.
- A climber's rope carries tension up to the anchor, and a crane cable carries the load of a container.
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Frequently asked questions
Is tension always equal to weight?
No. It depends on acceleration. A lift accelerating upwards has more tension than the weight.
Can a rope push?
No. Tension can only pull, which is why ropes go slack under compression.
Is tension the same along a light rope?
Yes, for a massless rope over a frictionless pulley, tension is the same at every point along it.
Related topics in Newton's Laws & Forces
Weight and normal force · Free-body diagrams · Net force and equilibrium · Atwood machine · Connected bodies · Elevator problems