Scalar quantities have magnitude only: mass, speed, temperature, energy, time.
Vector quantities have magnitude AND direction: force, velocity, acceleration, displacement, momentum.
SI units: length (m), mass (kg), time (s), current (A), temperature (K). Derived units: force (N = kg m/s2), energy (J = N m), power (W = J/s).
Prefixes: kilo (k) = 103, mega (M) = 106, milli (m) = 10−3, micro (μ) = 10−6.