Skip to main content
Physics LibreTexts

21.2: Introduction

  • Page ID
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    Torque is force acting at a distance, tending to cause rotation around a point.  The point about which the object rotates, the pivot point, is called the fulcrum.  When force is applied perpendicular to a lever arm, the amount of torque depends on the perpendicular force (F) applied and the length of the lever arm (d) through which the force acts.  

    Figure \(\PageIndex{1}\)


    \[\tau = Fd \nonumber \]

    Weight Force:

    \[W = mg \nonumber \]

    The amount of torque on one side of a fulcrum is equal and opposite to the amount of torque on the other side of the fulcrum.  This can allow a see-saw to be balanced if the two people sit at the correct distances from the pivot point.

    Figure \(\PageIndex{2}\)

    \[\tau_1 = -\tau_2 \nonumber \]

    Although the torque on each side of the pivot point is equal, the amount of force on each side of the pivot can be very different. 

    Figure \(\PageIndex{3}\)

    Contributors and Attributions

    21.2: Introduction is shared under a CC BY license and was authored, remixed, and/or curated by LibreTexts.

    • Was this article helpful?