# Definition of Torque?

1. May 9, 2015

### Timothy S

Hello,

I found the equation for torque to be t = r x F, where r and F are vectors. I have several questions about this; is r a true position vector, or is it the distance from the axis of rotation to the mass? is r the initial position of the mass with respect to the axis of rotation?

My current understanding of the equation is the r is the initial position of the mass, and that F is simply the force resolved into its x,y and z components. Is this true?

2. May 9, 2015

### Simon Bridge

if the rotation axis passes through point O and a force $\vec F$ is applied at point P, the $\vec r = \overrightarrow{OP}$ ... that definition works when rotation axis is perpendicular to both. There should have been a diagram with the equation.

3. May 9, 2015

### RaulTheUCSCSlug

r is a vector that points from the axis of rotation to where the force vector acts. The force is then the force acting on that point on r. The cross product of both vectors will give you the direction and magnitude of the torque. Therefore the force is the force that acts on the pivot arm, which can be simplified as x,y,z components.

4. May 9, 2015