5.7 Static Equilibrium

In the net force and the net torque on a rigid body are both 0, then it is in static equilibrium.

\displaystyle\sum_{i}\boldsymbol{F}_{i}=0\quad\text{and}\quad\sum_{i}% \boldsymbol{\tau}_{i}=0.

(5.74)

Note that we are free to choose any point as the origin to make finding the net torqe easier.

Example 5.7.

Consider a beam of mass 10kg and length 4m. It sits on a fulcrum placed 1m from one end of the beam, and is supported from the other end by a string. Find the tension in the string and the force of the beam on the fulcrum.

Example 5.8.

A ladder weighing 10kg rests on a smooth wall. Find the the static friction force between the floor and the ladder.

Example 5.9.

Consider a sign hanging from a bar attached to a wall supported by a string. Find the force between the bar and the wall.