Chapter 4 Review - Systems of Forces and Moments

Statics Textbook Sections 4.1 - 4.3 Summaries

Magnitude of the Moment

The magnitude of the moment of F about P is the product DF, where D is the perpendicular distance from P to the line of action F

Direction and Sign of the Moment

Direction

• CCW - if F would rotate an object pinned at P in the CCW direction about P

• CW - if F would rotate an object pinned at P in the CW direction about P

The moment of the force about P is

M_P = DF

• M is the moment, D is the distance, and F is the force

F in Components

Moment of F about point P = Moment caused by F_x about P + Moment caused by F_y about P

• the moment of F about P is equal to the sum of the moments of the the components of F about P

Moment

M_P = r x F

• r is a position vector from P to any point on the line of action of F

Magnitude of the Moment

|M_P| = D |F|

• where D is the ⊥ distance from P to the line of action of F