The following are the fundamental concept used in the engineering
mechanics
1. Force
In general force is a Push or Pull, which creates motion or tends
to create motion, destroy or tends to destroys motion. In engineering mechanics
force is the action of one body on another. A force tends to move a body in the
direction of its action, A force is characterized by its point of application,
magnitude, and direction, i.e. a force
is a vector quantity.
Units of force
The following force units are frequently used.
A. Newton
The S.I unit of force is Newton and denoted by N. which may be
defined as
1N = 1 kg. 1 m/s2
B. Dynes
Dyne is the C.G.S unit of force.
1 Dyne = 1 g. 1 cm/s2
One Newton force = 102 dyne
C. Pounds
The FPS unit of force is pound.
1 lbf = 1 lbm. 1ft/s2
One pound force = 4.448 N
One dyne force = 2.248 x 10ˉ6 lbs
2. Space
Space is the geometrical region occupied by bodies whose positions
are described by linear and angular measurement relative to coordinate systems.
For three dimensional problems there are three independent coordinates are
needed. For two dimensional problems only two coordinates are required.
3. Particle
A particle may be defined as a body (object) has mass but no size
(neglected), such body cannot exists theoretically, but when dealing with
problems involving distance considerably larger when compared to the size of
the body. For example a bomber aeroplane is a particle for a gunner operating
from ground. In the mathematical sense, a particle is a body whose dimensions
are considered to be near zero so that it analyze as a mass concentrated at a
point. A body may tread as a particle when its dimensions are irrelevant to
describe its position or the action of forces applied to it. For example the
size of earth is insignificant compared to the size of its orbits and therefore
the earth can be modeled as a particle when studying its orbital motion. When a
body is idealized as a particle, the principles of mechanics reduce to rather
simplified form since the geometry of the body will not be involved in the
analysis of the problem.
4. Rigid Body
A rigid body may be defined a body in which the relative positions
of any two particles do not change under the action of forces means the
distance between two points/particles remain same before and after applying
external forces. As a result the material properties of any body that is
assumed to be rigid will not have to be considered while analyzing the forces
acting on the body. In most cases the actual deformations occurring in the
structures, machines, mechanisms etc are relatively small and therefore the
rigid body assumption is suitable for analysis
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