Physics: Motion, Forces, Energy, Waves, and Electricity
Motion, force, energy
Physics questions reward one habit: describe the situation precisely before calculating. Distinguish speed (magnitude only) from velocity (magnitude with direction), and read graphs by slope - a distance–time slope is speed, a velocity–time slope is acceleration, and the area under a velocity–time graph is the distance travelled. A force is a push or pull with direction; the net force causes acceleration, which grows with force and shrinks with mass. When forces balance, motion continues unchanged (inertia) rather than stopping. Weight is a force measured in newtons; mass is measured in grams or kilograms - never mix the two.
Energy is conserved but transfers between kinetic, potential, thermal, electrical, and light forms, and some always spreads as heat. For a rolling or falling object, use the idea that lost height-energy equals gained kinetic energy instead of hunting for a formula.
Waves, sound, light, electricity
For waves, v = f × λ always holds. At a boundary the speed and wavelength change, but the frequency, fixed by the source, does not. Sound needs a medium and travels fastest in solids; light reflects at equal angles and bends toward the normal when entering a denser medium.
In circuits use Ohm's law, V = IR, plus two rules: series branches share the same current, parallel branches share the same voltage. Power is P = VI, and heat from a resistor is P × t.
Trap: two 6 Ω resistors in parallel give 3 Ω, not 12 Ω - a parallel combination is always smaller than its smallest branch.
Worked example. A wave of wavelength 0.50 m travels at 340 m/s: f = v / λ = 680 Hz.