Revise: Units and Measurements
Basic and derived units, systems of units, prefixes, measurement standards, and the instruments used to measure length, mass, and time.
Base units: length, mass, time, current, temperature, amount, luminous intensity. Derived units combine them.
N = kg·m/s².
Every quantity reduces to combinations of the seven base units — a fast way to check a formula.
Pressure = force/area = kg/(m·s²).
SI vs. CGS vs. FPS — always convert everything to one system before calculating.
3.2 kg = 3200 g.
Modern SI units are defined using constants of nature, not physical objects.
The second is defined by caesium atom vibrations.
Total reading = MSR + (VC × LC), with LC = 1 MSD − 1 VSD.
4.1 + (3×0.01) = 4.13 cm.
Total reading = MSR + (CSR × LC), with LC = pitch/divisions. About 10× finer than a vernier caliper.
0.5 + (20×0.001) = 0.52 cm.
A beam balance compares an unknown mass against known standard masses.
200+50+5 = 255 g.
A pendulum's period depends only on length and g, never on mass.
L=2.5 m → T ≈ 3.2 s.