Definition:Moment is the measure of the capacity or ability of the force to produce twisting or turning effect about an axis. This axis is perpendicular to the plane containing the line of action of the force. The magnitude of moment is equal to the product of the force and the perpendicular distance from the axis to the line of action of the force. The intersection of the plane and the axis is commonly called the moment center, and the perpendicular distance from the moment center to the line of action of the force is called moment arm.

From the figure above, O is the moment center and d is the moment arm. The moment M of force F about point O is equal to the product of F and d.

Simply put, themomentof a force is a measure of the tendency of a force to rotate an object about an axis. And can be mathematically expressed as: M = F x dwhere:M = moment of a forceF = magnitude of the force appliedd = perpendicular distance of the line of force from a point Sample Problem:In the figure shown below, assuming clockwise moments as positive, compute the moment of force F = 200 kg and force P = 165 kg about points A, B, C, and D. (Note: For this problem, kg is not converted into Newtons.)

Solution:

MEC30 | LectureMoment of a Force

Prepared by: Engr. Barrera

Moment of force F about points A, B, C, and D:

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Moment of force P about points A, B, C, and D:

answer * (this means that point A is on the line of action of force P)

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Practice Problems:

PROBLEM 1:

Determine:Moment @ Points A, B, C and D.Assume each box is 0.3m x 0.3m

PROBLEM 2:

Determine:Moment @ Points A, B, C and D.Assume each box is 0.3m x 0.3m