We were discussing various
important topics based on the basics of centrifugal compressor and hydraulic turbines in our previous
posts.

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Today we will be interested
here to start here a very important subject i.e. engineering mechanics with the
help of this post. We will secure here the various principles and concepts of
engineering mechanics such as basic concepts of force i.e. Concept of force system in engineering mechanics, understanding of free body diagram, equilibrium of
forces and rigid bodies, basics of supports, basics aspects of friction, basics
of trusses etc.

So, let us start here our
first important concept of engineering mechanics i.e. force system in
engineering mechanics. We will find out here the following concepts with the
help of this post i.e. force system in engineering mechanics.

- Concept of a force and effect of a force
- Newton’s Third law of motion
- Unit of force

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**Concept of force system in
engineering mechanics **

A force is basically the
action of one body on another body which changes or tends to change the motion
of the body or state of the body.

The effect of a force on a
body or object will be the combination of translation motion i.e. linear motion
and rotational motion.

Suppose if someone will
push us at the centre of our chest and if we do not resist against the pushing
force, what will be the motion of our body? Think it. Our body will move or
translate backward linearly.

Suppose if someone will
push us at the one edge of our chest and if we do not resist against the
pushing force, what will be the motion of our body? Think it again. Our body
will move or translate backward linearly as well as tend to rotate.

Therefore, in general any
force acting on an object will produce the combination of translation motion
i.e. linear motion and rotational motion.

A force is a vector
quantity and hence it will be represented by a vector. Force will be
characterized by following points as mentioned below.

- Point of applications
- Magnitude of force
- Direction of force

As we are well aware with
the Newton’s third law of motion, we can understand here that force will always
exist in the pairs.

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**Newton’s third
law of motion **

Newton’s third law of
motion tells us that for every action there will be an equal and opposite
reaction.

Let us see here two objects
1 and 2 as displayed here in following figure.

Let us assume that force
exerted by object 1 on object 2 is F

_{12}and force exerted by object 2 on object 1 is F_{21}.
According to Newton’s third
law of motion, force exerted by the object 1 on object 2 will be equal and
opposite in the direction with the force exerted by the object 2 on object 1.

Mathematically, we can
write here as

F

_{12}= - F_{21 }
Therefore, force will
always exist in the pairs. We must note it that action and reaction forces will
always act on different objects.

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**Force
interactions **

Once we draw the free body
diagram of a system where various forces are involved, force interaction will
be very important to consider during the drawing of free body diagram.

Force interactions could be
between systems in direct contact or those which are physically separated.

Let us consider the
following figure, where an object is placed over the table. Hence, there is
direct contact between the table and object.

We can also think the case
of aeroplane going in the sky. Aeroplane flying in the sky will have also an
interaction between the earth even there is no physical contact between the
aeroplane and earth.

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**Unit of force **

Unit of force is Newton and
we represent it as N.

Recall the equation or
formula for force derived from the Newton’s second law of motion.

F = m x a

Where, m is the mass of
object in Kg and a is the acceleration of the object in m/s

^{2}provided due to the application of force F.
Let us assume that mass
i.e. m is 1 kg and acceleration i.e. a produced due to the application of force
F is 1 m/s

^{2}. Think the above situation and we will have the information about the force F and it will be 1 N.
Therefore, we can define a
Newton as a force that develops an acceleration of 1 m/s

^{2}to a mass of 1 kg.
Therefore, we have introduced
here the basics of engineering mechanics where we have seen various basic
concepts in engineering mechanics such as concept of force system, unit of
force, effect of force and Newton’s third law of motion.

Further we will see other
concepts of engineering mechanics such as principle of transmissibility of forces, classification of force systems in engineering mechanics etc.

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which is given at right hand side of page for further and continuous update
from www.hkdivedi.com.

Further we will find out,
in our next post, principle of transmissibility of forces and its limitations.

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**Reference: **

Engineering Mechanics, By Prof K. Ramesh

Image courtesy:
Google

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