Lecture 02 BY

Engr Muhammad UsmanMechanical Engineering

DepartmentCECOS University

COURSE OUTLINE• Fundamental concept and principle of

mechanics, important vector quantity• Force system i.e concurrent• Non concurrent and parallel force system• Resultant of forces• Moment and couple• Equilibrium of forces (law & type) concept of

free body diagram

Force

• Is the action of one body on another.• A force is characterized by its point of

application, magnitude, and direction.• Force is a vector quantity.• We can separate the action of a force into two

effect , External and Internal.

Principle of Transmissibility

The principle of transmissibility states that a force may be applied at any point on its given line of action without altering the resultant effects of the force external to the rigid body on which it acts. Thus, whenever we are interested in only the resultant external effects of a force, the force may be treated as a sliding vector, and we need specify only the magnitude, direction, and line of action of the force, and not its point of application.

Because this course deals essentially with the mechanics of rigid bodies, we will treat almost all forces as sliding vectors for the rigid body on which they act.

Classification of Forces

• Force can be classified as either contact or body force.

• Contact Force: : a contact force is a force that acts at the point of contact between two objects.

• Contact force is the force in which an object comes in contact with another object.

Example of Contact force

• Force exerted on a body by a supporting surface.

Body Force

• Body force is generated by virtue of position of a body within force field.

• Example are gravitational, Electric and Magnetic fields.

Concentrated Force

• When the dimension of the area are very small compared with the other dimension of the body, we may consider the force to be concentrated at a point with negligible loss of accuracy.

Distributed force

• Force can be distributed over an area as in case of mechanical contact over a volume when a body force such as weight is acting or over a line as in case of the weight of the suspended cable.

Concurrent Force

• Two or more forces are said to be concurrent at a point if their line of action intersect at that point.

TWO DIMENSIONAL FORCE SYSTEM

Rectangular Component

Problem 2/1

Problem 2/2

Problem 2/3

Problem 2/4