Lesson 3 — Units (SI, Derived, Prefixes)
Units tell us what a number measures. In physics we use the SI system: 7 base units build all others. Treat units like algebra—multiply, divide, square, and cancel them.
SI Base Units (7)
SI Prefixes
Common Derived Units
Unit Algebra
Try it
Which is a base SI unit?
More practice
Worked examples
Example 1 — Force: N = kg·m/s²
by definition, so kg·m/s²
is the Newton.
Example 2 — Pressure: Pa = N/m² = kg/(m·s²)
because N = kg·m/s²
.
Example 3 — Prefix sense: 1 mm = 1000 μm
⇒ 1 mm is larger than 1 μm.