Last Updated: April 2026
Laws of Motion (Chapter 4, Class 11 Physics) is a foundational NEET chapter contributing 2-4 questions per year. It forms the bedrock of mechanics — without mastering Newton’s laws, you cannot solve problems in Work-Energy, Rotational Motion, or Gravitation. In NEET 2024, 3 questions came from this chapter with focus on pseudo forces in non-inertial frames, friction problems, and the impulse-momentum theorem.
NEET Laws of Motion — Chapter Snapshot
| Sub-Topic | NEET Questions | Priority |
|---|---|---|
| Newton’s First Law (Inertia) | 0-1 | MEDIUM |
| Newton’s Second Law (F=ma) | 1-2 | HIGH |
| Newton’s Third Law + Free Body Diagrams | 1 | HIGH |
| Friction (Static, Kinetic, Rolling) | 1-2 | HIGHEST |
| Impulse-Momentum Theorem | 0-1 | MEDIUM |
| Pseudo Force (Non-inertial frames) | 0-1 | MEDIUM |
Newton’s Three Laws — Concise Notes
First Law — Law of Inertia
A body continues in its state of rest or uniform motion in a straight line unless acted upon by an external force. Inertia is the tendency to resist change in state — proportional to mass.
- Inertia of rest: A stationary body tends to remain stationary
- Inertia of motion: A moving body tends to continue moving
- Inertia of direction: A body moving in a straight line resists directional change
NEET tip: First Law defines an inertial frame of reference (any frame where First Law holds).
Second Law — Law of Momentum
F = dp/dt = ma (when mass is constant)
- Net force = rate of change of momentum
- Force is a vector — direction same as acceleration
- 1 Newton = Force that gives 1 kg mass an acceleration of 1 m/s²
Third Law — Action-Reaction
For every action, there is an equal and opposite reaction.
- Action and reaction always act on different bodies
- They are simultaneous, equal in magnitude, opposite in direction
- They don’t cancel each other (different bodies)
Friction — Complete Analysis
| Type | When | Value | Formula |
|---|---|---|---|
| Static Friction (fs) | Body at rest, force applied | Variable (0 to μs·N) | fs ≤ μs·N |
| Limiting Friction | Just before sliding | Maximum static | fL = μs·N |
| Kinetic Friction (fk) | Body sliding | Constant | fk = μk·N |
| Rolling Friction (fr) | Body rolling | Smallest | fr < fk < fs |
Key relationship: μs > μk always. Static friction coefficient is always greater than kinetic.
NEET Problem — Friction on Inclined Plane
Block of mass m on incline of angle θ, coefficient of static friction μ. Maximum angle of inclination where block stays at rest: tan(θ) = μs → θ = arctan(μs). This angle is called the angle of friction (λ).
Impulse-Momentum Theorem
Impulse (J) = F × Δt = Δp = m(v-u)
- Impulse = area under F-t graph
- Impulse = change in momentum
- Units: N·s or kg·m/s
- NEET application: Cricket ball caught — large impulse absorbed over short time = large force (why catching with gloves helps)
Pseudo Force — Non-Inertial Frames
In an accelerating reference frame, an observer experiences a pseudo force = -ma (opposite to acceleration of the frame).
Example: In an elevator accelerating upward with acceleration ‘a’, apparent weight = m(g+a). In elevator accelerating downward, apparent weight = m(g-a). Free fall: apparent weight = 0 (weightlessness).
Practice MCQs — NEET Laws of Motion
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Frequently Asked Questions
Q1. How many NEET questions from this chapter?
2-4 per year. Friction and elevator problems appear most consistently.
Q2. Key formula to remember?
F=ma; f=μN; Impulse = Δp = F×t; Weight in elevator = m(g±a).
Q3. Best approach to friction problems?
Always draw a Free Body Diagram first. Identify normal force, then calculate friction = μN.
Q4. Are pseudo forces real?
No — they are mathematical tools for making Newton’s laws work in accelerating frames.
Q5. Daily NEET practice resource?
Visit NEET Gurukul for chapter-wise MCQ practice with AI evaluation.