First Law Of Motion

key notes :

Definition: The First Law of Motion, also known as Newton’s First Law of Motion or the Law of Inertia, states that:

“An object at rest stays at rest, and an object in motion stays in motion at a constant velocity unless acted upon by a net external force.”

In Simple Terms:

  • If something isn’t moving, it won’t start moving unless something pushes or pulls it.
  • If something is moving, it will keep moving in the same direction and at the same speed unless something changes that.

A stationary book on a table:

The book will stay at rest until you push it.

A car driving straight down a road:

The car will keep moving in a straight line at the same speed unless something like friction or a bump changes its motion.

Examples:

At Rest:

  • Example: A soccer ball lying on the grass will stay there until you kick it.
  • Why? The ball doesn’t move by itself; it needs a force to change its state.
Ball Is at rest.
Ball moves when we apply external force

In Motion:

  • Example: A skateboard rolling on a flat surface continues rolling until you stop it or it hits something.
  • Why? Without friction or another force, the skateboard would keep rolling forever.
The body is in the motion
The body will be in motion until and unless any external force acts on it

Why It Matters:

Understanding the First Law of Motion helps us explain how and why objects move or stay still. It’s the foundation for studying forces and motion in physics!

Visual Aid

Here’s a simple diagram to illustrate the concepts:

Stationary ObjectMoving Object


Let’s practice!