moment arm vs moment

[Francesco Mastrandrea]

what is the difference between moment arm and moment?I read the paragraph 12.6.1 of the opensim user's guide but I don't understand the difference indeed. Someone could explain again?
thanks

[Chris Zirker]

From physics, we know that a torque is essentially a rotational force and is calculated as:

torque = force * distance

Biomechanics people like to call rotational forces a "moment" instead of a "torque", but they are identical. When it comes to calculating rotational forces at a joint in the body, the above equation is:

moment = muscle force * moment arm

Wikipedia might be able to help you a bit more:
http://en.wikipedia.org/wiki/Torque#Moment_arm_formula

[Francesco Mastrandrea]

thanks, for my technical language moment is a torque, that's it. Now it's a definitely clear.

[Sam Hamner]

There is a small difference between a moment and a torque.

A moment measures the "rotational effect" of a force about a given point.

A torque (or moment couple), is a special case of a moment, where the forces are equal and opposite (i.e., their resultant is zero). A torque applied to a body is not dependent on a point.

Hence, a moment arm should be associated with a moment, not a torque.

Here's a good illustration of the difference: http://library.thinkquest.org/28388/Mec ... Moment.htm