Lesson–4 : Laws of Motion
PART–1 : Intermediate Physics Notes
1. Introduction
The Laws of Motion were formulated by Sir Isaac Newton to explain the relationship between force and motion. These laws form the foundation of Classical Mechanics and are applicable from everyday activities to advanced space science.
A clear understanding of these laws is essential for students preparing for:
- Intermediate Board Examinations
- IIT–JEE, EAMCET, NEET and other competitive exams
2. Force
A force is an interaction that can change the state of rest, the state of motion, or the shape of a body.
Effects of force:
- Change the speed of a body
- Change the direction of motion
- Change the shape or size of a body
Force is a vector quantity because it has both magnitude and direction.
3. Inertia
Inertia is the property of a body by virtue of which it resists any change in its state of rest or uniform motion.
Types of inertia:
- Inertia of rest
- Inertia of motion
- Inertia of direction
Important point: Inertia depends on the mass of the body. Greater the mass, greater is the inertia.
4. Newton’s First Law of Motion (Law of Inertia)
Statement:
A body continues in its state of rest or uniform motion in a straight line
unless acted upon by an external unbalanced force.
This law explains that:
- Rest and uniform motion are equivalent states
- No force is required to maintain motion
- Force is required only to change velocity
Examples include sudden starting and stopping of buses affecting passengers.
5. Momentum
The momentum of a body is defined as the product of its mass and velocity.
Momentum (p) = mv
Momentum is a vector quantity and plays a crucial role in understanding the second law of motion.
6. Newton’s Second Law of Motion
Statement:
The rate of change of momentum of a body is directly proportional to the applied force
and takes place in the direction of the force.
Mathematically:
F = dp/dt
For constant mass:
F = ma
This law provides the quantitative definition of force.
7. Newton’s Third Law of Motion
Statement:
For every action, there is an equal and opposite reaction.
Action and reaction forces:
- Are equal in magnitude
- Act in opposite directions
- Act on different bodies
Examples include walking, swimming, and recoil of a gun.
8. Applications of Laws of Motion
- Motion of a lift
- Motion on inclined planes
- Objects connected by strings and pulleys
These applications are extremely important for both Intermediate exams and IIT–JEE.
PART–1 Completed.
Conceptual foundation is ready. Next, we move to exam-oriented answers.
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