Tension
Definition
The pulling force transmitted through a rope, cable, or string when it is pulled tight at both ends.
Symbol: · Unit: N
Technical definition
An axial pulling force in a flexible connector. In an idealized massless rope over a frictionless pulley, tension is uniform throughout and acts along the rope's direction at each end.
Example
A 10 kg picture hanging from a wire puts the wire under about 98 N of tension — the wire pulls up on the picture and down on the hook with equal force.
Common confusion
Tension is not the same on both sides when the rope has mass or the pulley has friction — the ‘uniform tension’ rule only holds for ideal massless ropes. Real ropes also have a maximum tension before they snap.