Newton's First Law states that a body persists in its state of rest or uniform motion unless a net external force acts on it — defining inertia as the resistance to changes in motion. Newton's Second Law quantifies this: F = ma = dp/dt, where the net force equals the rate of change of momentum with dimensional formula [M^{1}$$L^{1}$$T^{-2}]. Newton's Third Law asserts that action and reaction forces are equal, opposite, and act on different bodies — not the same body. The normal force and weight on a resting block are balanced forces, not a Third Law pair, which is the most-tested NEET misconception. Apparent weight in a lift equals m(g + a) when accelerating upward and m(g − a) when accelerating downward, reaching zero in free fall (weightlessness). In an Atwood machine with masses m_{1} > m_{2}, the acceleration is (m_{1}−m_{2})g/(m_{1}+m_{2}) and the string tension is 2m_{1}m_{2}g/(m_{1}+m_{2}). Static friction is self-adjusting from zero to a maximum of μ_s N (limiting friction) and does not always equal μ_s N. Kinetic friction f_k = μ_k N is constant once sliding begins, with μ_k always less than μ_s. On an inclined plane, the normal force is mg cos θ (not mg), and the angle of repose satisfies tan θ = μ_s. Centripetal force for circular motion equals $mv^{2}$/r and is always provided by existing real forces — friction on level roads and the horizontal component of normal force on banked roads.