Note: this is one of those topics requiring math a little beyond the very basics. It's simpler than Introduction to Vectors, though, so I'd recommend you read it anyway. I would make another joke about how boring this is, but those jokes are getting old, don't you think?
First, we'll take a moment (yeah, yeah, pun intended) to clarify one point. When it was said that a moment depends on the distance between the force and the point, you may have wondered "Well, what distance?" [Example 7] If you look at Example A on the right, the two distances, represented by the dotted lines, are definitely different. On the other hand, the moments these forces create (we'll take for granted the magnitudes are equal) are the same. This is because "distance" is always the perpendicular distance to the line of the force. [Example 8] In Example B, the point of application of the force happens to be in an odd place in comparison to the point that the moments are being calculated around. So, you just extend the force's line. For moments, it doesn't matter where the force is applied. All that matters is how far away the force's line of action is. As for calculating the distance, I'll leave that up to you. The method you use will depend on how you have the force and point represented (drawn, as coordinates, or in some other, novel way). There are also ways to calculate the distance from vectors, but the math gets a lot more complicated than here and, well, I'd never be able to explain it. If you're interested, most textbooks on Statics (some listed in the Additional Sources of Information) seem to cover this topic.

So, you now have two numbers: the magnitude of a force, and the perpendicular distance from a point to that force. What do you do to find the moment? Multiply them. Simple as that. So, if you had a 10 Newton force 3 meters from a point, the moment would be 30 Newton-Meters. Notice the unit, Newton-Meters, that is used for moments (or Newton-Feet if newtons and feet are used, or Pound-Inches, etc.). You don't use just Newtons: those are for forces.

Back to Index || Last Topic: Moments, Not What You Thought They Were || Next Topic: Putting it All Together