Force system resultant, Cheat Sheet of Statics

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Engineering Mechanics

Statics

Soran University

Faculty of Engineering

Civil Engineering Department

Yousif J. Bas

(2022-2023)

CHAPTER OBJECTIVES  To explain the Moment of Force  To explain the Principle Moment  To explain the Moment of a Couple  To explain the Reduction of Simple Distributed Loading

Expected Outcomes  Able to solve the problems of MOF and MOC in the mechanics applications by using principle of moments

Force System Resultants

Hibbeler R. C., Engineering Mechanics , Statics, 13th edition, 2013

When a force is applied to a body it will produce a tendency for the body to rotate about a point that is not on the line of action of the force. This tendency to rotate is sometimes called a torque , but most often it is called the moment of a force or simply the moment.

Moment of a Force

Application of Moment (turning effect)

Application of Moment (turning effect)

Moment factor

Direction of Moment. The direction ofMO is defined by its moment axis , which is perpendicular to the plane that contains the force F and its moment armd. The right-hand rule is used to establish the sense of direction ofMO.

Example: For each case illustrated in the figure below, determine the moment of the force about point O.

Example:

Determine the moments of the 800 N force acting on the frame about points A, B, C and D.

Principle of Moments

A concept often used in mechanics is the principle of moments , which states that the moment of a force about a point is equal to the sum of the moments of the components of the force about the point.

This method is generally easier than

finding the same moment usingMO = Fd.

Example: Determine the moment of the force in the figure below about point O.

Example:

ForceF acts at the end of the angle bracket in the figure below. Determine the

moment of the force about pointO.

Solution: