Please wait for the animation to completely load.

We talk about the magnitude of the torque as the amount of force perpendicular to the radius arm on which it acts. No radius arm, no torque. Torque is positive (out of the page) if F acts to rotate the object counterclockwise via the right-hand rule (RHR) and negative if F acts to rotate the object clockwise (again, via the RHR). Restart.

In order to mathematically describe torque, we must use the mathematical construction
of the vector or cross product. Torque is the vector product of the radius vector
and the force vector, **r** × **F**. The magnitude
of the torque is r F sin(θ), and the direction of the torque is determined
by the RHR. θ is the angle between the two vectors, and A and B are the magnitudes
of the vectors
**r** and **F**, respectively. Drag the tip of either
arrow
**(position is given in meters)**. The
**red arrow is r **and the
**green arrow is F**. The magnitude
of each arrow is calculated as well as the cross product.

The direction of the torque,
**r** × **F**, is determined by the RHR (point
your fingers toward
**r**, curl them into the direction of
**F**, and the direction that your thumb points is the direction of
the torque. Therefore,

τ = **r** × **F** = r F sin(θ) with the
direction prescribed by the RHR,

where **r** is the moment arm on which the force acts and **F** is the force.

Illustration authored by Mario Belloni and Wolfgang Christian.

HTML updated for JavaScript by Ricky Davidson.

Physlets were developed at Davidson College and converted from Java to JavaScript using the
SwingJS
system developed at St. Olaf College.