Measurements, Units, and Scientific Notation

Section 1Measurements need units

A measurement is incomplete without a unit. Saying a desk is 1.2 tells you almost nothing; saying 1.2 m tells you its length. Here's the trick: always write the unit beside the number, especially in lab tables.

Section 2Fundamental and derived quantities

Fundamental quantities are basic ones, such as length, mass, time, temperature, and electric current. Derived quantities are made from fundamental quantities. For example, area is length times width, so its unit is square metres.

Section 3SI units and prefixes

SI units are standard units used in science, such as metre, kilogram, second, ampere, and kelvin. Prefixes change the size of a unit: milli- means one thousandth, centi- means one hundredth, and kilo- means one thousand. In plain words, that means 1 km = 1000 m and 1 cm = 0.01 m.

Section 4Scientific notation

Scientific notation writes numbers as a value from 1 to less than 10 multiplied by a power of 10. For example, 3500 m can be written as 3.5 x 10^3 m. Watch out: the decimal movement decides whether the power of 10 is positive or negative.