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Tension is a pulling force transmitted through a rope, cable, or similar object when it is pulled tight by forces acting at both ends. It acts along the length of the object and always pulls, never pushes. Tension is fundamental in mechanical systems, from simple pulleys to complex structural applications.

Unlike compression, which pushes inward, or shear forces, which slide surfaces past each other, tension exclusively pulls outward along an object's length. Tension cannot exist in isolation—it requires forces acting at both ends pulling away from each other. This directional characteristic makes tension unique among mechanical forces.

Tension magnitude depends on the applied load, the mass of the object being pulled, and gravitational acceleration. In a rope supporting a hanging mass, tension equals the weight of the object. In dynamic systems, acceleration and friction also influence tension values throughout the system.

In an ideal pulley with a single rope supporting a mass, tension equals the weight of the suspended object. For systems with multiple masses or accelerating objects, apply Newton's second law to each component separately, then solve simultaneously. Assume massless ropes and frictionless pulleys unless stated otherwise.

In an ideal massless rope with no friction, tension remains constant along its entire length because no net force acts on any segment. If tension varied, the rope segment would accelerate infinitely. This uniform tension assumption simplifies analysis and is valid for most undergraduate mechanics problems.

When a rope accelerates, tension adjusts to provide the net force required for acceleration. Using Newton's second law, tension must overcome both the weight of suspended objects and provide the additional force needed for acceleration. The tension value increases or decreases depending on acceleration direction and magnitude.