If you want to feel how much in 1 Newton , hold your palm horizontally and put a hundred gram
weight on it; the force that you feel is about 1N.
Of course you cannot always measure the force applied by accelerating objects. For example if
you are pushing a wall, how much force you are applying cannot be measured by observing the
acceleration of the wall because the wall is not moving. However once we have adopted a
measure of force, we can always measure it by comparing the force applied in some other
In the first part of the course i.e. Statics we consider only equilibrium situations. We will
therefore not be looking at F = ma but rather at the balance of different forces applied on a
system. In the second part - Dynamics - we will be applying F = ma extensively.
Third Law: Newton's third law states that if a body A applies a force F on body B , then B also
applies an equal and opposite force on A . (Forces do not cancel such other as they are acting on
two different objects)
Thus if they start from the position of rest A and B will tend to move in opposite directions. You
may ask: if A andB are experiencing equal and opposite force, why do they not cancel each
other? This is because - as stated above - the forces are acting on two different objects. We shall
be using this law a lot both in static as well as in dynamics.
After this preliminary introduction to what we will be doing in the coming lectures, we begin
with a review of vectors because the quantities like force, velocities are all vectors and we should
therefore know how to work with the vectors. I am sure you have learnt some basic
manipulations with vectors in your 12th grade so this lectures is essentially to recapitulate on
what you have learnt and also introduce you to one or two new concepts.
You have learnt in the past is that vectors are quantity which have both a magnitude and a
direction in contrast to scalar quantities that are specified by their magnitude only. Thus a
quantity like force is a vector quantity because when I tell someone that I am applying Xamount of force, by itself it is not meaningful unless I also specify in which direction I am
applying this force. Similarly when I ask you where your friend's house is you can't just tell me
that it is some 500 meters far. You will also have to tell me that it is 500 meters to the north or
300 meters to the east and four hundred meters to the north from here. Without formally
realizing it, you are telling me a about a vector quantity. Thus quantities like displacement,
velocity, acceleration, force are vectors. On the other hand the quantities distance, speed and