| Cue (Questions) | Notes (Answers / Key Points) |
|---|---|
| State Newton's First Law | A body remains at rest or in uniform motion in a straight line unless acted upon by a net external force. Inertia ∝ mass. |
| State Newton's Second Law | F = ma = dp/dt. Net force equals rate of change of momentum. Dimension: [M^{1}$$L^{1}$$T^{-2}]. |
| State Newton's Third Law | F_AB = −F_BA. Equal and opposite forces on DIFFERENT bodies. Not the same body. |
| Is N and mg an action-reaction pair? | NO. They act on the SAME body (the block). A-R pairs always act on different bodies. |
| Apparent weight when lift goes UP | W' = m(g + a) — person feels heavier. |
| Apparent weight when lift goes DOWN | W' = m(g − a) — person feels lighter. |
| Apparent weight in free fall | W' = m(g − g) = 0 — weightlessness. |
| Atwood machine: acceleration? | a = (m_{1} − m_{2})g / (m_{1} + m_{2}), with m_{1} > m_{2}. |
| Atwood machine: tension? | T = 2m_{1}m_{2}g / (m_{1} + m_{2}). Always: m_{2}g < T < m_{1}g. |
| Is static friction always μ_s N? | NO. f_s is self-adjusting: 0 ≤ f_s ≤ μ_s N. It equals μ_s N only at limiting (about-to-slide) condition. |
| Kinetic friction formula? | f_k = μ_k N (constant once sliding begins). μ_k < μ_s always. |
| Angle of repose? | tan θ = μ_s. At this angle, body is on the verge of sliding. |
| Centripetal force on level road? | Friction provides it: v_max = √(μrg). |
| Banking formula (no friction)? | tan θ = /(rg). v = √(rg tan θ). |
| Momentum conservation condition? | F_ext = 0. Then m_{1}u_{1} + m_{2}u_{2} = m_{1}v_{1} + m_{2}v_{2}. |
| What is impulse? | J = F· = . Area under F–t graph. Dimension: [M^{1}$$L^{1}$$T^{-1}]. |
Summary: Newton's laws connect force, mass, and acceleration via F = ma and F = dp/dt. Momentum is conserved when no external force acts. Apparent weight in a lift depends on acceleration direction. Atwood machine provides two-equation FBD practice. Friction is self-adjusting (static) or constant (kinetic), with μ_s > μ_k > μ_r. Circular motion needs a centripetal force supplied by real forces (friction, tension, gravity). Banking removes dependence on friction for safe speed.