Mechanics is the largest and most fundamental topic in IB Physics. It covers motion (kinematics), forces (dynamics), energy, and momentum. Mastery here is essential — mechanics concepts underpin almost every other topic.
Displacement (vector) vs distance (scalar). Velocity v = Δs/Δt; acceleration a = Δv/Δt. SUVAT equations for uniform acceleration: v = u + at, s = ut + ½at², v² = u² + 2as, s = ½(u+v)t. Graphs: gradient of s-t gives v; gradient of v-t gives a; area under v-t gives displacement. Free fall: a = g ≈ 9.81 m/s² downward.
First law (inertia): an object stays at rest or constant velocity unless acted on by a net force. Second law: F_net = ma (in the direction of net force). Third law: action-reaction pairs (equal magnitude, opposite direction, different objects). Free-body diagrams: show all forces on one object. Common forces: weight (mg), normal, tension, friction (f ≤ μN), drag.
Work W = Fs·cosθ (J). Kinetic energy Ek = ½mv². Gravitational PE: Ep = mgh near surface. Work-energy theorem: W_net = ΔEk. Conservation of energy: total energy is constant in an isolated system. Power P = W/t = Fv. Efficiency = useful energy output / total energy input × 100%.
Linear momentum p = mv (kg·m/s). Impulse J = FΔt = Δp. Newton\'s second law: F = Δp/Δt. Conservation of momentum: in a closed system, total momentum before = total momentum after. Elastic collisions conserve both momentum and kinetic energy. Inelastic: only momentum conserved. Explosions: zero initial momentum splits into equal and opposite momenta.
Follow this framework: (1) Draw a clear diagram showing the situation. (2) Draw a free-body diagram of the object of interest with all forces labelled. (3) Choose a coordinate system (usually: positive in the direction of motion). (4) Apply Newton\'s second law in each direction: ΣF = ma. (5) Solve the equations. For energy problems: identify initial and final states, apply conservation of energy or the work-energy theorem.
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