Moments

Moments are the rotation caused by a force acting at a distance from the center of resistance (CR). A moment is defined by the following equation:

Moment (M) = Force (F) x Distance(D) from CR

Since Fa and Fb are acting at a distance from CR, both forces create a moment.

Which of the following forces does not have a moment?

Fc, because Mc = Fc X 0 = 0

Given: F = 10g D = 10mm

What is M?

Answer is 100g-mm

Moments can also be created by couples. To calculate the moment of a couple, use the following equation:

Moment (M) = Magnitude of a force (F) x Distance (D) between the two forces

Given: F = 10g D = 5mm

What is M?

Answer is M = 10g X 5mm = 50g-mm

A couple always causes rotation around CR, regardless of where the couple is placed on the object.

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Last Update: August 20,1998
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