In mechanics, tension is defined as which of the following?

• A. The force resisting motion between two surfaces.
• B. A reaction force exerted by a stretched string on the object it stretches.
• C. The twisting moment that causes rotation.
• D. The pressure exerted by a fluid.

Answer: (B)

Tension is the pulling force transmitted along a string, rope, or cable when it is stretched. This force acts on the objects at its ends, directing away from the string and toward the object it pulls.

The statement describing a stretched string exerting a force on the object it stretches best matches this idea: the string pulls on the object, delivering the tension force that resists being pulled apart. In other words, tension is the reaction force the string applies to the object attached to it.

The other descriptions refer to different forces: friction resists sliding between surfaces, a twisting moment is a torque that causes rotation, and fluid pressure is the force exerted by a fluid per unit area.