CHAPTER-1 FORCE ANALYSIS AND EQUILIBRIUM
Engineering mechanics is the branch of science that considers the motion of bodies and the effects of forces on that motion. It may be divided into two parts
Statics deals with the special case of a body at rest or a body that moves with a constant velocity.
Dynamics is further divided into Kinematics and Kinetics. Kinematics is concerned with rates of change of geometrical quantities in a moving system; it does not involve the concept of force. Kinetics treats the causes and the nature of motion that results from specified forces.
- A particle has a mass, but a size that can be neglected. For example, the size of the earth is insignificant compared to the size of its orbit and thereafter the earth can be modelled as a particle when studying its orbital motion.
- A rigid body can be considered as a combination of a large number of particles in which particles remain at a fixed distance from one another both before and after applying a load.
An agent which produces or tends to produce, destroy or tends to destroy motion.
SI Unit: Newton (N)
System of forces
When two or more than two forces of different magnitude and direction act upon a body, they constitute a system of forces.
Two or more forces that act at the same point are called concurrent forces. Concurrent forces need not have the same direction. They simply act at the same point.
If concurrent forces do have the same direction, they are collinear forces.
Two or more forces whose directed arrows lie in the same plane are called coplanar forces.
- Since two concurrent forces always lie in a common plane, they are always coplanar.
- Three or more concurrent forces are not necessarily coplanar.
PRINCIPLE OF TRANSMISSIBILITY
The state of rest or of motion of a rigid body is unaltered if a force acting on the body is replaced by another force of the same magnitude and direction but acting anywhere on the body along the line of action of the applied forces.
RESULTANT OF FORCE
It is possible to find a single force that will have the same effect as that of a number of forces acting on a body. The single force is called resultant force and the process of finding out the resultant force is called the composition of forces. The reverse of the composition of forces is called resolution of force.
PARALLELOGRAM LAW OF FORCES
If two forces, acting simultaneously on a particle, be represented in magnitude and direction by the two adjacent sides of a parallelogram, which passes through their point of intersection, their resultant force is represented, both in magnitude and in direction, by the diagonal of the parallelogram drawn through their point of intersection. Let two forces P and Q are represented by OP and OQ respectively, on two sides of the parallelogram. Now the parallelogram OPRQ is completed and the resultant is represented by diagonal.
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