Nature of Science
Domain 1: Nature of Science
The Nature of Science domain tests how physics knowledge is built and measured: SI units and dimensional analysis, uncertainty and significant figures, experimental design, and the historical transitions from Galileo and Newton to Einstein. Expect items on distinguishing models from reality, evaluating claims, and interpreting graphs.
Core rules
- SI base units: kg, m, s, A, K, mol, cd. Derived units follow algebraically (N = kg·m/s², J = N·m, W = J/s).
- Accuracy is closeness to a true value; precision is repeatability. Random error scatters readings; systematic error shifts them all (zero error, miscalibration).
- Significant figures: multiplication and division keep the least number of significant figures; addition and subtraction keep the least decimal place.
- Uncertainty propagation: for products and quotients add fractional uncertainties; for sums add absolute uncertainties.
- A hypothesis is testable; a theory is a well-tested explanatory framework; a law describes a regularity. They are not a ladder of proof.
Worked example
A metal sample has mass 12.4 ± 0.1 g and volume 4.8 ± 0.2 cm³. Density ρ = 12.4/4.8 = 2.58 g/cm³. Fractional uncertainties are 0.1/12.4 ≈ 0.008 (0.8%) and 0.2/4.8 ≈ 0.042 (4.2%). Adding gives about 5%, so Δρ ≈ 0.05 × 2.58 ≈ 0.13. Report ρ = 2.6 ± 0.1 g/cm³, keeping two significant figures because the volume has two.
Traps
- Reporting 2.583 g/cm³ ignores the two-significant-figure volume.
- Calling repeated identical readings 'accurate' - they may be precisely wrong.
- Using a formula without checking units; dimensional analysis catches many errors.
- Treating a model (ray optics, ideal gas) as literally true rather than as a valid approximation with limits.
- Confusing 'theory' with 'guess' in history-of-science items.