Newton's Laws Short Notes

Exam-focused notes for JEE, NEET and Class 11 Physics with formulas, mistakes and MCQs.

Core idea

Newton's Laws explain the relation between force, mass and motion. Most mechanics problems become simple when you draw a correct free-body diagram and apply net force equation along each axis.

Three laws

First Law: A body continues in rest or uniform motion unless net external force acts on it.
Second Law: Net force equals mass times acceleration: F = ma.
Third Law: Every action has an equal and opposite reaction, acting on a different body.

Common mistakes

Forgetting normal force.
Mixing action-reaction pair with balanced forces.
Taking friction direction without checking motion tendency.
Using F = ma before resolving forces into components.

Practice MCQs

Q1. A body remains at rest unless acted upon by external net force. This is:

First law
Second law
Third law
Law of gravitation

Q2. SI unit of force is:

Joule
Newton
Watt
Pascal

Q3. If mass is 2 kg and acceleration is 3 m/s², force is:

5 N
6 N
1.5 N
9 N

Q4. Action and reaction forces act on:

Same body
Different bodies
Only moving bodies
Only at rest

Q5. Friction acts:

Along normal
Opposite relative motion tendency
Always forward
Only in air

FAQs

What are Newton's three laws?

First law: an object stays at rest or uniform motion unless acted on by net force. Second law: F = ma. Third law: every action has equal and opposite reaction.

Why is Newton's Laws important for JEE and NEET?

It is the base of Mechanics. Questions on friction, circular motion, pulleys, blocks and connected bodies depend on Newton’s laws.

What is the most common mistake?

Students draw incomplete free-body diagrams. Always mark weight, normal reaction, tension, friction and applied force before solving.

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