Engineering Mechanics fundamental of forces

Basics of Engineering Mechanics

1. Engineering Mechanics

2. SYSTEM OF FORCES When two or more forces act on a body, they are called to form a system of forces.Force system is basically classified into following types. i . Coplanar forces ii. Collinear forces iii. Concurrent forces iv. Coplanar concurrent forces v. Coplanar non- concurrent forces vi. Non-coplanar concurrent forces vii. Non- coplanar non- concurrent force

3. COPLANAR FORCES: Theforces , whose lines of action lie on the same plane, are known as coplanar forces. COLLINEAR FORCES:The forces, whose lines of action lie on the same line, are known ascollinear forces. They act along the same line. Collinear forces may act in the opposite directions or in the same direction. Fig 1.1 CONCURRENT FORCES: The forces, whose lines of action pass through a common point, are known as concurrent forces.The concurrent forces may or may not be collinear

4. ACTION AND REACTION: Action means active force. Reaction means reactive force. When a body having a weight W (=mg) is placed on a horizontal plane as shown in Fig 1.8, the body exerts a vertically downward force equal to „W‟ or „mg‟ on the plane. Then „W‟ is called action of the body on the plane. According to Newton‟s 3rd law of motion, every action has an equal and opposite reaction. But action and reaction never act on the same body. So, the horizontal plane will exert equal amount of force „R‟ on the body in the vertically upward direction. This vertically upward force acting on the body is called reaction of the plane on the body.

5. POLYGON LAW OF FORCES It is an extension of Triangle Law of Forces for more than two forces, which states, “If a number of forces acting simultaneously on a particle, be represented in magnitude and direction, by the sides of a polygon taken in order then the resultant of all these forces may be represented, in magnitude and direction, by the closing side of the polygon, taken in opposite order.

6. 1.5 MOMENT OF A FORCE It is the turning effect produced by a force, on the body, on which it acts. The moment of a force is equal to the product of the force and the perpendicular distance of the point, about which the moment is required and the line of action of the force. Mathematically, moment, M = P × l where P = Force acting on the body, andl = Perpendicular distance between the point, about which the moment is required and the line of action of the force. Moment of a force about a point is the product of the force and the perpendicular distance of the point from the line of action of the force.