Newton’s First Law Of Motion

The Basic Idea

1. Anything is a body. For example, your phone, keyboard, pen – all of them. So when I say “a body” it means anything you can imagine. So let’s take example of you.

Either I can say – You are going to school on a bicycle.

OR

A body is going to school on a bicycle.

2. When you consider movement, there are only 2 states – rest and in motion. So either you are moving or you are not moving (being at rest)

You can’t do both right.

Because by definition – rest = not moving

And in motion = moving

3. Suppose you are riding in car with speed 50 km/hr

If you are traveling in a straight line, you will say – your car is in uniform motion.

Another example,
You are accelerating the car and the speed in increasing – 20, 26, 42 and son 

It doesn’t matter if you are in a straight line, you will say- your car is in non-uniform motion.

Another example, 
Suppose you are riding in car with speed 50 km/hr

If you are traveling randomly NOT straight line, you will say – your car is in non-uniform motion. Hence, you conclude – uniform motion is in straight line and constant velocity at intervals. Everything else is non-uniform motion

4. A force is said to be balanced when the 2 opposing forces of the same value interact. Imagine you pushing your friend and she doing the same. If the force is the same then no one will move. Here, the force is said to be balanced.

Now, imagine if you put in more force then the net force is positive and your friend will move. Hence, for any disturbance to occur, you need unbalanced force.

Let’s enter – first law of motion
“A body continues to be in a state of uniform motion or rest unless acted by an external unbalanced force.”

Once you know all the meanings, it seems obvious.

If no one stops you then you will keep on going, right?

Imagine yourself running, if no one comes on your way and you don’t stop – then you will keep on running in the same direction.

As long as an unbalanced force (you trying to stop or someone coming in your way) acts on you.

That’s the gist of it.

In space, there is no resistance, imagine you apply a force to  a ball. It won’t stop because there is no unbalanced force (not even air resistance) to stop it. It will keep on going in a straight line unless it gets interrupted by something.

We will call this “inertia” this phenomena as inertia.

EXAMPLE,
When you are in a bus standing you move along with the bus. Hence, your speed is the same as that of bus.

When the bus is stopped by brake, you do stop – but your body will tend to keep going forward because of the first law (inertia). So you feel a jerk in your body.

Similarly when the bus starts you feel the jerk because you are at rest. And your body will be at rest, but it is forced to move. Hence, the jerk because of inertia. (first law)