JEE Mains 2026 Revision: Newton’s Laws of Motion Notes, Formulas, Tricks & PYQ Insights

 

Newton’s Laws of Motion – JEE Mains 2026 Revision Capsule

A high-yield, exam-ready NLM capsule. Covers forces, FBD logic, friction behavior, pulleys, block systems, constraints, and tricky JEE traps—with quick illustrations and mini problems.

1. Newton’s First Law (Inertia)

A body remains in rest or uniform velocity unless acted upon by an external force. Inertia types: rest, motion, direction.

2. Newton’s Second Law

Core equation: \( \vec{F} = m\vec{a} \)
Momentum: \( \vec{F} = \frac{d\vec{p}}{dt} \)
Impulse: \( J = \Delta p \)

3. Newton’s Third Law

Action–reaction pairs act on different bodies. They do not cancel each other.

4. Free-Body Diagram (FBD) – The JEE Gamechanger

Always isolate the body. Use axes along motion. Forces to consider: Weight (mg), Normal (N), Tension (T), Applied force (F), Friction (f), Pseudo force (in non-inertial frames).

JEE Trap: Students often forget the normal changes when acceleration is vertical or when an object is in an elevator.
Example: In an accelerating lift:
If moving up with acceleration \( a \): \( N = m(g + a) \) If moving down: \( N = m(g - a) \)

5. Tension – What JEE Loves to Twist

Massless string → same tension everywhere.
Frictionless pulley → same tension on both sides.

Two-block system under force \(F\): Acceleration: \( a = \frac{F}{m_1 + m_2} \)
Tension: \( T = \frac{m_1 F}{m_1 + m_2} \)

Mini Question: Two blocks of 2 kg and 3 kg are pulled by 25 N. Find tension.
Solution: \( a = \frac{25}{5} = 5\,\text{m/s}^2 \) \( T = 2 \times 5 = 10\,\text{N} \)

6. Friction – Silent Villain of JEE

Static friction: \( f_s \leq \mu_s N \)
Kinetic friction: \( f_k = \mu_k N \)
Important: Static friction adjusts itself & can be zero.

On an incline: Parallel: \( mg\sin\theta \) Normal: \( N = mg\cos\theta \)

JEE Trap: Many PYQs involve the block not moving even though force is applied. Students incorrectly use \( f_s = \mu_s N \) always. Correct idea: check required friction first.

7. Pulleys & Constraints

Atwood machine acceleration: \( a = \frac{(m_1 - m_2)g}{m_1 + m_2} \)
Tension: \( T = \frac{2 m_1 m_2 g}{m_1 + m_2} \)

Mini Question: If \( m_1 = 4\text{kg} \) & \( m_2 = 1\text{kg} \), find acceleration.
Solution: \( a = \frac{3g}{5} \)

JEE Trap: If a pulley itself accelerates, tension on two sides becomes unequal. This appears in advanced PYQs.

8. Circular Motion Linked Concepts

Centripetal force requirement: \( F_c = \frac{mv^2}{r} \) No new force — it's supplied by existing ones (tension, gravity, friction).

JEE Trap: Centrifugal force is not real in inertial frames. It exists only in non-inertial rotating frames as a pseudo force.

9. Block on Block – A JEE Favourite

System acceleration: \( a = \frac{F}{m_1 + m_2} \)

Friction needed for top block: \( f = m_2 a \)

Mini Illustration:
If \( f > \mu_s m_2 g \), top block slips. If \( f \leq \mu_s m_2 g \), both move together.

10. Pseudo Forces (Non-Inertial Frame Magic)

If frame accelerates with \( a_0 \), add a pseudo force \( F_p = m a_0 \) opposite to the direction of acceleration.

JEE Trap: Students often apply pseudo force even in inertial frames. Use it ONLY if you choose the accelerating frame.

11. Quick JEE Shortcuts

• Treat multi-block systems as one mass first, then split. • Always check limiting friction in friction problems. • Use constraints early for pulley problems. • Draw FBD before writing equations. • Assume friction direction; equations correct it. • Convert everything to one axis; avoid mixing components.

12. Quick JEE-Level Check Question

Question:
A 5 kg block on a horizontal surface is pulled by 20 N. \( \mu_s = 0.5 \), \( \mu_k = 0.3 \). Find acceleration.

Solution:
Max static friction = \( \mu_s mg = 0.5 \times 5 \times 9.8 = 24.5\,N \). Required friction = 20 N → less than max → block does not move. Acceleration = 0.

This expanded NLM capsule is built for ultra-fast but deep revision — designed to hit every PYQ pattern with clarity and confidence.