INTRODUCTION
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: Statics deals with the special case of a body at rest or a body that moves with a constant velocity.
- Dynamics: 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.
FORCE
An agent which produces or tends to produce, destroy or tends to destroy motion.
SI Unit: Newton (N)
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 they 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.
RESULTANT OF FORCE
It is possible to find a single force which 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 composition of forces. The reverse of the composition of forces is called resolution of force.
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.
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.
POLYGON LAW OF FORCES
When the forces acting on a body are more than two, the triangle law can be extended to polygon law. Polygon Law states that if a number of coplanar concurrent forces acting simultaneously on a body are represented in magnitude and direction by the sides of a polygon, taken in order, then their resultant can be represented by closing side of the polygon in magnitude and direction in the opposite order.
NON-COPLANAR FORCE SYSTEM
RESOLUTION AND RESULTANT OF FORCE IN SPACE
CONDITIONS OF EQUILIBRIUM
The term equilibrium implies that either the body is at rest or it moves with a constant velocity. A body is said to be in static equilibrium when the resultant force in it must be zero and the body must have no tendency to rotate.
The resultant force causing motion should be zero.
i.e. SF = 0. It means that SH = 0 And SV = 0.
The resultant moment causing rotation should be zero.
i.e. SM = 0 about any point.
FREE BODY DIAGRAM
One of the most useful aids for soling a statics problem is the free body diagram (FBD). A free body diagram is a sketch of the body that shows the body (by itself, free of the other part of the system) and all the forces applied to it, that is, all forces acting on the body. Fig shows free body diagrams.
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