1.2 Force types.pptx

INTRODUCTION  Engineering Mechanics are divided into two main groups. 1. Statics 2. Dynamics INTRODUCTION STATICS  The branch of Engineering Mechanics which deals with the forces and their effects while acting upon the bodies at rest. DYNAMICS The branch of Engineering Mechanics wh...

INTRODUCTION  Engineering Mechanics are divided into two main groups. 1. Statics 2. Dynamics INTRODUCTION STATICS  The branch of Engineering Mechanics which deals with the forces and their effects while acting upon the bodies at rest. DYNAMICS The branch of Engineering Mechanics which deals with the forces and their effects while acting upon the bodies in motion.  Dynamics is further divided into two groups. 1. Kinetics 2. Kinematics KINETICS The branch of Dynamics which deals with the bodies in motion due to the application of forces. KINEMATICS The branch of Dynamics which deals with the bodies in motion without considering the forces which are responsible for motion. FORCE It may be defined as an agent which produces or tends to produce, destroy or tends to destroy the motion of a body. Example: a horse applies force to pull a cart and to set it in motion EFFECT OF A FORCE  A force while acting on a body may  Change the motion of body  Retard the motion of body  Give rise to the internal stresses of the body  In order to find the effect of force on body, we must know the nature, magnitude and line of action of force. UNIT OF FORCE In MKS system magnitude of force expressed in Kilogram force (kgf)  In Sl system magnitude of force expressed in newton (N) Resultant Force 1kgf=9.81N SYSTEM OF FORCES When two or more forces act on a body, they are called to form a system of forces. SYSTEM OF FORCES  Coplanar forces  Collinear forces  Concurrent forces  Coplanar concurrent forces.  Coplanar non-concurrent forces  Non-coplanar concurrent forces  Non-coplanar non-concurrent forces COPLANAR FORCE The forces, whose lines of action lie on the same plane, are known as coplanar forces. COLLINEAR FORCE The forces, whose lines of action lie on the same line, are known as collinear forces CONCURRENT FORCE  The forces, which meet at one point, are known as concurrent forces.  The concurrent forces may or may not be collinear COPLANAR CONCURRENT AND NON- CONCURRENT FORCE Coplanar concurrent forces The forces, which meet at one point and their lines of action and also also lie on the same plane, are known as coplanar concurrent forces. Coplanar non-concurrent forces The forces, which do not meet at one point, but their lines of action lie on the same plane, are known as coplanar non- concurrent forces. NON-COPLANAR CONCURRENT AND NON- CONCURRENT FORCE Non-coplanar concurrent forces The forces, which meet at one point, but their lines of action do not lie on the same plane, are known as non-coplanar concurrent forces. Non-coplanar non-concurrent forces The forces, which do not meet at one point and their lines of action do not lie on the same plane, are called non-coplanar non-concurrent forces. RESULTANT FORCE If a number of forces, P, Q, R... etc. are acting simultaneously on a particle, then it is possible to find out a single force which could replace them. Adding of vectors This single force is called resultant force COMPOSITION OF FORCES  The process of finding out the resultant force, of a number of given forces, is called composition of forces or compounding of forces METHODS FOR THE RESULTANT FORCE  Methods for finding out the resultant force of a number of given forces are  Analytical method  Method of resolution ANALYTICAL METHOD FOR RESULTANT FORCE  The resultant force, of a given system of forces, may be found out analytically by the following methods  Parallelogram law of forces  Method of resolution  PARALLELOGRAM LAW OF FORCES Definition  It states if two forces acting simultaneously on a particle be represented in magnitude and direction by the two adjacent sides of a parallelogram  Their resultant is represented in magnitude and direction by the diagonal of the parallelogram which passes through their point of intersection. MATHEMATICAL CALCULATION FOR RESULTANT FORCE CONTD.. CONTD… PROBLEM Two forces of 100 N and 150 N are acting simultaneously at a point. What isthe resultant of these two forces, if the angle between them is 45°? SOLUTION LAWS FOR THE RESULTANT FORCE The resultant force, of a given system of forces, may also be found out by the following laws :  1. Triangle law of forces.  2. Polygon law of forces. TRIANGLE LAW OF FORCES  It states, “If two forces acting simultaneously on a particle, be represented in magnitude and direction by the two sides of a triangle, taken in order ; their resultant may be represented in magnitude and direction by the third side of the triangle, taken in opposite order.” POLYGON LAW OF FORCES  It is an extension of Triangle Law of Forces for more than two forces Definition  It states that “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”.  LAW OF FORCES  Polygon law of forces Where A, B, C and D are the forces and R = Resultant force  Blue arrow show anticlockwise of forces  Red arrow show clockwise of resultant which show reverse order REFERENCE R. S. Khumi, A text book of Engineering Mechanics, S. Chand & company ltd.