Torque: Lever Arms, Direction, and Net Torque

All flashcards

Torque

A force's tendency to change an object's rotation about a chosen point or axis.

Vector definition of torque

For position vector $\vec{r}$ and force $\vec{F}$, $\vec{\tau}=\vec{r}\times\vec{F}$.

Torque magnitude

$|\vec{\tau}|=rF\sin\theta$, where $\theta$ is the angle between position and force vectors.

Lever arm

The perpendicular distance from a pivot to the force's line of action.

Net torque

The vector sum of the torques acting about the same origin or axis.

Quiz questions

1. What can happen to the torque of a force when the chosen pivot changes?Answer: It can change because the position vector is measured from the selected pivot.
2. What does the lever arm measure for a force about a pivot?Answer: The perpendicular distance from the pivot to the force's line of action.
3. What does the right-hand rule determine for a torque?Answer: The direction of the torque vector from the directions of $\vec{r}$ and $\vec{F}$.
4. How is net torque calculated for several forces in planar fixed-axis rotation?Answer: Add the signed torques about the same axis.
5. What does zero net torque imply about angular acceleration around a fixed axis?Answer: The applied net torque produces no angular acceleration about that axis.