Force And Laws Of Motion Class 9 CBSE Notes - Chapter 9

CBSE Class 9 Science Chapter 9 Notes: Force And Laws Of Motion

Force and laws of motion class 9 introduce the laws set down by Isaac Newton and the concept of force. These are essentially the fundamentals of physics and forms the backbone of every physical context known to humans. But how do we define the concept of force and what do the laws of motion imply?

First Law of Motion

“An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.”

Also called the Law of Inertia, an object will stay at rest or in motion indefinitely, unless an external or unbalanced force acts upon this object.

Eg: Water in a bottle continues moving forward even though the bottle has come to a halt.

Second Law of Motion

“The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force.”

This law of motion is also called the Law of Force and Acceleration. It means that force is equal to the change in momentum per change in time. For a constant mass, force equals mass times acceleration.

Eg: It takes more effort to push a truck than to push a bike.

Third Law of Motion

“To every action, there is an equal and opposite reaction and they act on two different bodies.”

Out of the three laws of motion, this is the most popular and widely known. Eg: While jumping, we exert our force downwards to the ground, and consequently we move up. This is because the ground is exerting the same force in the opposite direction.

Force And Laws Of Motion Class 9 Notes – Questions

  1. State the three laws of motion.
  2. What is the Law of Inertia?
  3. Explain the Law of Force and Acceleration.

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