Chapter 2 Measurements: SI Units, Significant Figures, and Errors (Vocabulary)

Vocabulary flashcards covering SI units, measurement uncertainty, significant figures, errors, and basic unit conversions from the lecture notes.

SI (International System of Units)

A standardized system of measurement units used in science; base units include meter (length), kilogram (mass), second (time), etc.

Uncertainty

The range of possible error in a measurement; the last digit typically carries an associated uncertainty.

Estimated decimal place

The last significant figure is in an estimated decimal place; the uncertainty is often half the smallest division.

Smallest division

The smallest increment on a measuring instrument’s scale that determines the precision of a measurement.

Significant figures (sig figs)

Digits that carry meaning about precision in a measurement; leading zeros are not significant; trapped zeros are significant; trailing zeros may or may not be, depending on decimal presence.

Leading zeros

Zeros to the left of the first nonzero digit; not counted as significant figures.

Trailing zeros

Zeros at the end of a number; their significance depends on the presence of a decimal point (often not counted unless specified).

Trapped zeros

Zeros between nonzero digits; always significant.

Multiplication/Division sig figs rule

In multiplication or division, the result has as many significant figures as the factor with the fewest sig figs.

Addition/Subtraction decimal places rule

In addition or subtraction, the result should have the same number of decimal places as the value with the fewest decimal places.

Kilogram (kg)

SI base unit of mass; 1 kg = 1000 g.

Microgram (µg)

A microgram; 1 µg = 1×10^-6 g (1 g = 1,000,000 µg).

Conversion factor

A factor used to convert from one unit to another by multiplying or dividing (e.g., 1 inch = 2.54 cm).

Random errors

Errors that cause measurements to scatter above and below the true value; not biased in a single direction.

Systematic errors

Errors that bias measurements in the same direction (always too high or always too low).

Illegitimate errors (human errors)

Avoidable errors due to mistakes such as spills or calculation mistakes; can be reduced or eliminated.

Accuracy

How close a measurement is to the true value.

Precision

How reproducible repeated measurements are; high precision means measurements cluster tightly around a value.

Reporting uncertainty

Measurements are reported with the last-digit uncertainty and have units (e.g., 12.3 cm ± 0.1 cm).

Example: 12.1 cm × 1.3745 cm

Product rule example: multiplication of lengths yields 16.6 cm^2 when rounded to the fewest sig figs (3 sig figs overall).

Addition example: 12.2 g + 1.480 g

Sum rounded to the least number of decimal places, giving 13.7 g (1 decimal place).

1.23 g to kg and µg

1.23 g = 0.00123 kg and 1,230,000 µg.

191.0 pounds sig figs

191.0 lb has 4 significant figures (the trailing zero after the decimal is significant).

30.0 cm to inches

30.0 cm = 11.8 inches (1 in = 2.54 cm; 3 sig figs).

1.8 inches to cm

1.8 inches = 4.57 cm (3 sig figs).

Final reminder on figures and units

All lab and test calculations must maintain the correct number of significant figures and include proper units.

Summary topics

Uncertainty, precision, accuracy; random, systematic, illegitimate errors; significant figures.