Talha's Physics Academy
Unit # 3: Dynamics — Newton’s Laws of Motion
Lecture Overview
This lecture from Talha's Physics Academy provides an in-depth review and explanation of Newton's Three Laws of Motion, inertia, force, acceleration relationships, and practical examples for Class 11 Physics (Unit 3: Dynamics).
Source Video: Newton's Laws of Motion - Unit 3 Dynamics - Class 11 Physics
Q.1 State and explain Newton’s Laws of Motion.
(1) Newton’s First Law of Motion
Newton’s first law of motion consists of two parts:
- (i) The first part states that a body cannot change its state of rest or uniform motion in a straight line itself unless it is acted upon by some unbalanced force to change its state. It can also be stated that a moving body when not acted upon by some net force would have free motion, that is uniform motion in a straight line.
- (ii) The second part states that force is an agent which changes or tends to change the state of rest or uniform motion i.e., it produces acceleration in the body.
The first law of motion is also known as the law of inertia.
Inertia
Everybody in this universe has a property that it always offers some resistance to the change of its state. This property is known as Inertia and it is because of the mass of the body. Therefore we need force to overcome inertia for the change of its state, either rest or motion.
(2) Newton’s Second Law of Motion
Newton’s second law states that: “When a force acts upon a certain body, the acceleration produced is proportional to the force and it is in the direction of the force.”
Where:
- \(F\) = Net force on the body
- \(m\) = mass of the body
- \(a\) = acceleration in the body
It is clear from the above equation that the acceleration for a certain force on the body is inversely proportional to the mass of the body.
(3) Newton’s Third Law of Motion
Newton’s third law can be stated as: “To every action there is an equal but opposite reaction.”
The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the force on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs — equal and opposite action-reaction force pairs.
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