What is Force?
Let me tell you what you will probably read in your text books
Force is a push or pull upon an object right?
While this cannot be classified as incorrect,
it hardly explains anything about the concept of force
 
This is what you will assume after reading this definition
you will imagine a stationary object on the ground
and someone pushing it or pulling it.
Yes, when force is applied
the stationary object will move
but this does not explain the concept of force entirely.
Before we move on to the definition of force, lets clear a few
misconceptions about it.
Let me ask you a question,
this ball is lying at rest on the ground
it's stationary, not moving at all.
Is there any force acting on it?
Listen to my question carefully,
are there any forces acting on the ball
when it is stationary?
If your answer was a no, or if you didn't have an answer
it means you don't know the concept of force yet.
The answer is yes! There are forces
acting on this ball.
There is a gravitational force, which is trying to pull the ball towards
the centre of the Earth.
And the ground is applying an equal force, exactly in the
opposite direction.
This force is called the normal force
Because these two forces are balanced, they do not change the
position of an object. The net force
acting on the ball is zero.
So what does this tell you? Just humans
pushing or pulling is not the only kind of force.
And just because there are forces acting on an object
will not mean the object will move. For the
object to move, there has to be some net force.
So now let's say a person softly kicks the ball,
what happens then? Yes, the position of the
ball changes. Why did the position
change? It's because there was another magnitude
of force acting on it, and this time,
the forces were not balanced. The ball
moved, and there was displacement.
But hold on, why did the ball stop moving after
covering 15 meters? The ball started moving
at a pace, and then slowly came to a halt.
If there is no force from the other side to stop it,
how did it stop?
Was there a force which stopped it? Yes,
It was friction that stopped the ball.
While the force you applied was toward the right,
the force of the friction was toward the left.
Let's make it even more interesting,
Assume your screen to be a frame of reference for this example.
Also assume that this straight horizontal line is a
a frictionless floor, and there is no air resistance.
The ball appears from the left of your screen, and moving
towards the right at a uniform velocity
of 2m/s. The only two forces
acting on the ball are the gravitational and the normal forces
which net each other out.
In this setting, will the ball ever stop moving?
No it won't, it will continue to move along the same path
at the same speed, unless there is another
external force which acts on it. Here as the forces are balanced
the ball will continue to move at 2m/s
Most people assume that if the object is moving,
then there is some net force acting on it, and that's not true.
An object will continue to move at uniform velocity
even if the net force on it is zero.
So there are two things we've learnt here.
First, if the object is stationary, and the net force
acting on it is zero, then it will
continue to remain at rest.
Second, if the object is moving at uniform velocity,
and the net force acting on it is zero, then it will
continue to move at that same uniform velocity.
Now when this ball is moving at 2m/s
and there is an external force applied from the left, what
will happen?
Yes, the ball will accelerate. It's
velocity will change. Let's say the  velocity
changes to 3m/s
after this external force is applied. After that,
the ball will continue to move at 3m/s, unless
acted upon by another external force.
So nobody's really seen or touched force
it can only be understood by knowing what happens to an
object when force is applied to it. If
the body is stationary, do not assume that there is no
force acting on it.
And if the body is in uniform
motion, do not assume that there is some net
force acting on it. So what is force?
Force is a push or a pull upon an object, resulting from its
interaction with another object.
So when you kick the ball
The ball also exerts a force onto your leg.
But as the force of your leg gets stronger
the ball moves to the right.
There are many more concepts we need to understand about force.
Which we will cover in the next video.
