Scientific Inquiry, Measurement, and the Nature of Science
What to know
Scientific inquiry is a cycle of question, hypothesis, prediction, controlled experiment or observation, data analysis, and revision. Know the vocabulary: independent variable (what the experimenter changes), dependent variable (what is measured), control group (no treatment, for comparison), constants (everything held fixed), and confounding variable (an uncontrolled factor that offers an alternative explanation). Distinguish a hypothesis (testable, falsifiable prediction) from a theory (a broad, well-supported explanatory framework) and a law (a concise, repeatedly confirmed regularity, often mathematical). Science cannot address questions that are not empirically testable.
Measurement
Use SI units and prefixes: kilo- (10³), centi- (10⁻²), milli- (10⁻³), micro- (10⁻⁶), nano- (10⁻⁹). Precision is repeatability (how close repeated measurements are to each other); accuracy is closeness to the true value; random error scatters results, systematic error shifts them all one way. Significant figures reflect measurement certainty: in multiplication and division, the answer carries the least number of significant figures; in addition and subtraction, the least number of decimal places. Convert with dimensional analysis so units cancel.
Traps
Questions often mislabel a control group as a constant, call a well-tested theory "just a guess," or ask for precision when the data show bias. Watch for graphs whose axes are not linear or that imply causation from correlation. A single trial, a small sample, or no replication weakens a conclusion regardless of how clean the result looks.
Rule of thumb and worked example
Convert 250 mL to liters: 250 mL × (1 L / 1000 mL) = 0.250 L. If a student measures a 10.0 g sample three times as 9.8, 9.9, and 9.9 g, the results are precise but slightly inaccurate (low) - a systematic error, not random scatter.