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AP®PhysicsCollege BoardPhysics 1: Algebra-BasedStudy GuidesUnit 2: Force & Translational DynamicsTensionTension

Tension (College Board AP® Physics 1: Algebra-Based): Study Guide

Ann Howell

Written by: Ann Howell

Reviewed by: Caroline Carroll

Updated on

Tension force

Ideal pulleys

  • An ideal pulley is a pulley that

    • has negligible mass

    • rotates about an axle through its center of mass with negligible friction

Ideal pulley system

A close-up view of an old, weathered metal pulley with a thick rope running through the wheel, used for lifting or moving heavy objects.
An ideal pulley system has negligible mass and negligible friction and rotates around a fixed axle

  • An ideal pulley has negligible mass so should not be considered as part of the mass of a system

  • A pulley enables the motion and change in direction of any particles attached to the string, cable or chain

Examples of pulleys in action

Two systems of particles connected by light, inextensible strings passing over smooth pulleys, moving in opposite directions. Text beneath explains the concept.
An ideal pulley has negligible mass and negligible friction.

  • Pulleys have many practical applications, including the movement of heavy objects

  • For example, boats are unloaded using a pulley system

    • When a force is applied to the chain on one side of the pulley, this moves the object out of the boat, which is on the other side of the pulley

Using a pulley to unload a boat

TO DO WHEN HAVE IMAGE
A force applied to a rope running over a pulley makes it easier to move heavy objects

Tension force

  • Tension is the macroscopic net result of forces that segments of a string, cable, chain, or similar system exert on each other in response to an external force

    • Tension in a vertical system with a string or similar object often arises from the external gravitational force

    • Tension in a horizontal system with a string or similar object often arises from the external forces of friction or another contact force

Diagram showing forces in a string. Left: repulsive electron forces. Right: at tension, attractive forces, uneven electrons, temporary dipoles form.
When a string is under tension there are attractive forces between oppositely charged particles.

Examples of tension applied horizontally and vertically

A setup for measuring wire extension: copper wire clamped with wooden blocks, ruler for measurement, tape marker, pulley, weights, and G-clamp securing to end of the wire to the bench
Tension is applied to the wire by weights added to the vertically hanging end and the contact force provided by the G-clamp

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    Author
    Reviewer
    Ann Howell

    Author: Ann Howell

    Expertise: Physics Content Creator

    Ann obtained her Maths and Physics degree from the University of Bath before completing her PGCE in Science and Maths teaching. She spent ten years teaching Maths and Physics to wonderful students from all around the world whilst living in China, Ethiopia and Nepal. Now based in beautiful Devon she is thrilled to be creating awesome Physics resources to make Physics more accessible and understandable for all students, no matter their schooling or background.

    Caroline Carroll

    Reviewer: Caroline Carroll

    Expertise: Physics & Chemistry Subject Lead

    Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.