Questions
6 questions on average
Difficulty
Medium-Hard
Importance
Core foundation for entire physics syllabus
Overview
Laws of Motion form the foundation of classical mechanics, governing the relationship between a physical body and the forces acting upon it. This topic is essential for competitive and board exams as it provides the framework for solving problems related to dynamics, equilibrium, and constrained motion. Mastering this requires a deep understanding of Free Body Diagrams (FBDs) and the vector nature of forces.
Newton's Laws of Motion
These three laws define the behavior of objects at rest or in motion and describe the interaction between objects. Understanding inertial and non-inertial frames is critical for solving advanced problems involving pseudo-forces.
- First Law: Law of Inertia
- Second Law: F = dp/dt or F = ma
- Third Law: Action-reaction pairs
- Impulse = Change in Momentum (J = Δp)
- Constraint motion basics
Friction Dynamics
Friction is a contact force that opposes relative motion or the tendency of motion between surfaces. Exam questions frequently combine friction with Newton's laws to test your ability to determine if an object slides or remains stationary.
- Static friction limit: fs ≤ μsN
- Kinetic friction: fk = μkN
- Angle of repose equals angle of friction
- Rolling friction is generally lower than sliding
- Always define direction against relative motion
Circular Dynamics
When an object moves in a circular path, it requires a net centripetal force directed toward the center of curvature. You must be able to resolve forces into radial and tangential components to solve complex banking or vertical circle problems.
- Centripetal Force: Fc = mv²/r
- Centripetal Acceleration: ac = v²/r
- Banking of roads: tan θ = v²/(rg)
- Minimum speed at top of vertical loop: v = √gr
- Tension in vertical circle: T = mv²/r + mg cos θ
Formula Sheet
Fnet = ma
fs,max = μsN
fc = mv²/r
tan θ = v²/(rg)
J = FΔt = Δp
Exam Tip
Always resolve forces into components aligned with the acceleration vector and the perpendicular axis to simplify equations into a manageable system.
Common Mistakes
- Failing to draw a complete Free Body Diagram (FBD) including all contact and field forces.
- Confusing the direction of friction; it always opposes relative motion, not necessarily the applied force.
- Applying Newton's Second Law (F=ma) in non-inertial frames without adding the appropriate pseudo-force.
More Revision Notes
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