Physics
Core toolkit
Start with measurement: SI base units, prefixes (kilo, centi, milli, micro), and the difference between mass (kg) and weight (N). Motion: speed = distance ÷ time, acceleration, and reading distance–time versus velocity–time graphs. Forces: Newton's three laws, friction, momentum, and balanced versus unbalanced forces. Work, energy and power (W = Fd, P = W/t) and the conservation of energy. Density and pressure, including P = ρgh for liquids. Heat versus temperature, and thermal expansion. Waves: frequency, wavelength and wave speed, plus the speed of sound in air. Light: reflection, refraction, and simple ray diagrams. Electricity: current, voltage and resistance through Ohm's law (V = IR), series and parallel circuits, and power P = VI.
Traps
- Speed vs velocity: velocity needs a direction; displacement is not distance travelled.
- Graph slopes: slope of a distance–time graph is speed; slope of a velocity–time graph is acceleration.
- Unconverted units: 20 cm must become 0.2 m before substitution.
- Series vs parallel: in series the current is the same everywhere and voltage splits; in parallel the voltage is the same and current splits.
- Mass on the Moon is unchanged although weight is smaller.
Rule of thumb
Write the formula, list known values with units, convert, substitute, then check that the answer's unit is correct. A wrong unit means a wrong method, so redo it.
Worked example: A 12 V battery is connected across a 4 Ω resistor. I = V/R = 12/4 = 3 A. Power P = VI = 12 × 3 = 36 W.