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 net force
  
  Inertia: tendency to resist change in state of motion
  Inertia ∝ mass (heavier object = more inertia)
  
  Examples: passenger lurches forward when bus brakes (inertia of motion)
            dust falls from carpet when beaten (inertia of rest)
            coin falls into glass when card is flicked (inertia of rest)

SECOND LAW:
  F_net = ma (net force = mass × acceleration)
  Vector equation: direction of acceleration = direction of net force
  
  Impulse: J = F × Δt = Δ(mv) = change in momentum
  Impulse-momentum theorem: J = mv_f - mv_i
  
  Unit of force: 1 Newton = 1 kg·m/s²

THIRD LAW (Action-Reaction):
  For every action, there is equal and opposite reaction
  SAME magnitude, OPPOSITE direction, act on DIFFERENT bodies
  Action and reaction CANNOT cancel (they act on different objects)
  
  Examples: gun recoil, rocket propulsion, swimming, walking

LINEAR MOMENTUM:
  p = mv (vector quantity)
  Conservation: if F_net = 0 (no external force), total momentum is conserved
  p_initial = p_final for isolated system
  Application: collisions, explosions, rocket propulsion

TYPES:
  Static friction: prevents relative motion; adjustable up to maximum
    f_s ≤ μ_s × N (static friction coefficient × normal force)
    Maximum static friction: f_s(max) = μ_s × N
  
  Kinetic friction: opposes relative motion (sliding friction)
    f_k = μ_k × N (constant once sliding)
    μ_k < μ_s (always: kinetic less than static maximum)
  
  Rolling friction: very small (wheels, ball bearings)

ANGLE OF FRICTION (λ):
  tan λ = μ (friction coefficient)
  Angle of repose (θ): angle at which object just starts to slide on incline
  tan θ = μ_s → θ = angle of friction for static case

FRICTION ON INCLINE:
  Normal: N = mg cos θ | Friction (static): f = mg sin θ (when stationary)
  Condition for sliding: mg sin θ > μ_s × mg cos θ → tan θ > μ_s
  Acceleration when sliding: a = g(sin θ - μ_k cos θ)

FRICTION IS NOT ALWAYS HARMFUL:
  Useful: walking, car tyres on road, brakes, writing, machinery
  Reduced by: lubricants, ball bearings, polishing, streamlining

UNIFORM CIRCULAR MOTION:
  Speed constant but direction changes → acceleration exists
  Centripetal acceleration: a = v²/r = ω²r (directed INWARD toward centre)
  Centripetal force: F = mv²/r = mω²r (net force required for circular motion)
  
  This is NOT a separate force — it IS the net inward force
  The force providing centripetal force: friction, tension, normal, gravity

CIRCULAR MOTION EXAMPLES:
  Car on flat road: friction provides centripetal force (f = mv²/r)
  Car on banked road: N sin θ provides centripetal force
    Ideal banking angle: tan θ = v²/rg (no friction needed at this speed)
  
  Conical pendulum:
    T cos θ = mg (vertical equilibrium)
    T sin θ = mv²/r = mω²r (centripetal)
    → tan θ = ω²r/g | Period: T = 2π√(l cos θ/g)
  
  Vertical circular motion (ball on string):
    At bottom: T - mg = mv²_B/r → T = mg + mv²_B/r (maximum tension)
    At top: T + mg = mv²_T/r → T = mv²_T/r - mg
    Minimum speed at top: T = 0 → v_min = √(gr)
    Using energy conservation: v_B² = v_T² + 4gr

PSEUDO FORCE:
  When solving in non-inertial (accelerating) reference frame
  Add pseudo force = -ma (opposite to frame's acceleration)
  Example: person in accelerating car feels pushed back → pseudo force outward
  Centrifugal force: pseudo force in rotating frame (outward)

COMMON NEET QUESTION TYPES:
  Find tension in string during vertical circular motion
  Maximum speed on banked/unbanked road without skidding
  Impulse calculation from force-time graph area
  Conservation of momentum in collision/explosion
  Angle of repose and friction coefficient relationship

FORMULA SHEET:
  F = ma | J = Δp = F·Δt | p = mv
  f_s(max) = μ_s N | f_k = μ_k N | tan(θ_repose) = μ_s
  a_c = v²/r = ω²r | F_c = mv²/r
  Escape velocity: NOT in this chapter (see Gravitation)

COMMON MISTAKES:
  Confusing centripetal force with centrifugal (centrifugal is pseudo, only in rotating frame)
  Applying Newton's 3rd law: remember action-reaction on DIFFERENT bodies
  Friction direction: always OPPOSES relative motion (or tendency of motion)