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SEMESTER:- 2ND SEMESTER

SUBJECT:-ENGINEERING MECHANICS

CHAPTER : 1

TOPIC : FUNDAMENTALS OF ENGINEERING MECHANICS

PREPARED BY :-

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EFFECTS OF A FORCE

*It may change the motion of a body. i.e. if a body is at rest, the force may set it in motion. And if the body is already in motion, the force may accelerate it.

*It may retard the motion of a body.

* It may retard the forces, already acting on a body, thus bringing it to rest or in equilibrium

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CHARACTERISTICS OF A FORCE

  • 1. Magnitude of the force (i.e., 10 N, 20 kN, 5 kN, etc.)

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  • 2. The direction of the line, along which the force acts (i.e., along OX, OY, at 60° North of East etc.). It is also known as line of action of the force.

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  • 3. Nature of the force (i.e., whether the force is push or pull). This is denoted by placing an arrow head on the line of action of the force.

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  • 4. The point at which (or through which) the force acts on the body

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PRINCIPLE OF TRANSMISSIBILITY OF FORCES

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It states, “If a force acts at any point on a rigid body, it may also be considered to act at any other point on its line of action, provided this point is rigidly connected with the body.”

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RESULTANT FORCE

  • If a number of forces are acting simultaneously on a particle, then it is possible to find out a single force which could replace them i.e., which would produce the same effect as produced by all the given forces. This single force is called resultant force and the given forces R ... etc. are called component forces.

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PARALLELOGRAM LAW OF FORCES

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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 may be represented in magnitude

and direction by the diagonal of the parallelogram, which passes through their point of intersection.”

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RESOLUTION OF A FORCE

  • The process of splitting up the given force into a number of components, without changing its effect on the body is called resolution of a force.
  • A force is, generally, resolved along two mutually perpendicular directions.

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PRINCIPLE OF RESOLUTION

  • It states, “The algebraic sum of the resolved parts of a no. of forces, in a given direction, is equal to the resolved part of their resultant in the same direction.”
  • In general, the forces are resolved in the vertical and horizontal directions.

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POLYGON LAW OF FORCES

  • It 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.”

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MOMENT

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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.

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TYPES OF MOMENTS

  1. Clockwise moments.

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  • Anticlockwise moments.

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VARIGNON’S THEOREM

  • It states, “If a number of coplanar forces are acting simultaneously on a particle, the algebraic sum of the moments of all the forces about any point is equal to the moment of their resultant force about the same point.”

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COUPLE

  • A pair of two equal and unlike parallel forces (i.e. forces equal in magnitude, with lines of action parallel to each other and acting in opposite directions) is known as a couple.
  • As a matter of fact, a couple is unable to produce any translatory motion (i.e., motion in a straight line).
  • But it produces a motion of rotation in the body, on which it acts.
  • The simplest example of a couple is the forces applied to the key of a lock, while locking or unlocking.

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