Basics of Mechanics

1. 20ME205 – Engineering
Mechanics
( Core – II Subject)
Unit – I
Introduction to Engineering Mechanics
Date: 16 April 2021
A Presentation by:
Mr. R.L. SANKARLAL, M.E., MISTE., MSAE., (Ph.D).,
Asst. Professor (Gr-II) /Mech.,
R.M.K. Engineering College

2. Relative Importance & Scope of the subject in
Mechanical Engineering
Design of
Transmission
Systems, Machine
Elements
Strength
of
Materials
Kinematics
of
Machinery
Engineering
Mechanics

3. Mechanics
Mechanics of Rigid
Bodies
Mechanics of
Deformable Bodies
Mechanics of
Fluids
Statics Dynamics
Kinematics
Kinetics

4. Force Action of one body on the other (push or pull)
Point of
Application
Direction
Magnitud
e

5. What is the need of knowing
MECHANICS?
Mechanics Deals with forces

6. acceleration
,
Studying Internal effect
of
as
forces on a body such
stresses (internal
resistance),
change in shape
etc.
Rigid body mechanics
Deformable body mechanics
Studying
forces on
External effect of
a body such as
acceleration,
velocity,
displacement etc.
Studying Internal effect of
as
forces on a body such
stresses (internal resistance),
change in shape etc.

7. Statics
 Deals with forces and its
effects when the body is at rest
Dynamics
 Deals with forces and its effects when
the body is in moving condition
Truss Bridge IC Engine

8. Rigid Body Mechanics
Negligible deformation (no deformation) under the action of forces.
Assuming 100% strength in the materials. Large number of particles
occupying fixed positions with each other.
Actual structures and machines are never rigid under the action of
external loads or forces.
But the deformations induced are usually very small which does not
affect the condition of equilibrium.

9. Particle Mechanics
 Treating the rigid body as a particle which is negligible in
size when compared to the study involved. (very small
amount of matter which is assumed as a point in a space).
Example: studying the orbital motion of earth

10. Types of Forces
Concurrent coplanar
forces
Collinear forces
Concurrent non-coplanar
Non Concurrent coplanar
(Parallel)

11. Components of a Force
PlaneForce
SpaceForce

12. Couple Two equal and opposite forces are acting at
some distance forming a couple

13. How Rotational
Effect will change
with distance?

14. Free Body Diagram (FBD)
Isolated body from the structure of machinery which shows all the forces
and reaction forces acting on it.

15. Examples for free body diagram

16. Parallelogram law:
Two forces acting on a particle can be replaced by the single
component of a force (RESULTANT) by drawing diagonal of the
parallelogram which has the sides equal to the given forces.
Parallelogram law cannot be proved mathematically . It is an
experimental finding.

17. The two vectors can also be added by head to tail by using triangle law.
Triangle law states that if three concurrent coplanar forces are acting at
a point be represented in magnitude and direction by the sides of a
triangle, then they are in static equilibrium.

18. Lami’s Theorem states that if three concurrent coplanar forces
are acting at a point, then each force is directly proportional to
the sine of the angle between the other two forces.

19. Lami’s theorem considering only
the equilibrium of three forces
acting on a point not the stress
acting through a ropes or strings
The principle of transmissibility is
applicable only for rigid bodies
not for deformable bodies

20. F1
F2
F5
F4
F3
A B
E
D
C
Polygon Law of Forces
“If many number of forces acting at
a point can be represented as a sides
of a polygon, then they are in
equilibrium”

21. Questions, Queries
& Discussions