Newton's Laws form the foundation of classical mechanics. The First Law (Inertia) establishes that bodies maintain their state of rest or uniform motion unless acted upon by a net external force, defining inertial frames. The Second Law (F = ma) quantifies the relationship between force and acceleration — it is the workhorse equation for all mechanics problems. The Third Law establishes that forces always come in equal and opposite pairs acting on different bodies.

Friction is a contact force that opposes relative motion or its tendency. Static friction is self-adjusting (0 to $mu_s$*N), while kinetic friction is constant ($mu_k$*N, where $mu_k$ < $mu_s$). The angle of repose equals arctan($mu_s$).

The Free Body Diagram (FBD) is the most important problem-solving tool. Isolate each body, draw ALL forces ON it (weight, normal, tension, friction, applied), choose axes, and apply F = ma along each axis. For connected systems, use constraint relations (string length conservation) to relate accelerations.

Key configurations include the Atwood machine (a = (m1-m2)$\frac{g}{m1+m2}$), block-on-table with hanging mass, inclined planes, and multi-block systems. For non-inertial frames (elevators, accelerating vehicles), add a pseudo force F = -$ma_{frame}$ to apply Newton's laws correctly.

Common errors include confusing action-reaction pairs with balanced forces on one body, using mu*N for static friction regardless of the applied force, and treating "ma" as a force in the FBD.