Mechanics · Quick Reference

Units & Measurements Cheat Sheet

Mechanics · Lesson 2/19

In one line: units give physical quantities meaning, and the International System of Units (SI) provides a single consistent standard used by scientists worldwide.

Key Ideas

1SI Base Units. Meter (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for current, kelvin (K) for temperature, mole (mol) for amount of substance, candela (cd) for luminous intensity.

2SI Prefixes. Prefixes scale units by powers of 10: kilo- (1000x), centi- (1/100), milli- (1/1000), micro- (1/1,000,000).

3Derived Units. Combinations of base units, like the newton (N = kg*m/s^2) for force, or the joule (J = kg*m^2/s^2) for energy.

4Significant Figures. The digits in a measurement that carry meaningful precision; more significant figures indicate a more precise measurement.

5Unit Conversion. Converting a measurement from one unit to another using a known conversion factor, such as 1 km = 1000 m.

Worked Examples

Convert 5 kilometers to meters.

5,000 meters

Convert 2,500 grams to kilograms.

2.5 kilograms

What is the SI unit of force, and what base units does it combine?

Newton (N) = kg*m/s^2

Formulas

1 km = 1000 m

1 kg = 1000 g

1 hour = 3600 s

Practice Yourself

Convert 3 km to meters.

3,000 m

Convert 1,500 m to km.

1.5 km

What does the prefix 'milli-' mean?

1/1000