SI Units, Prefixes, and Scientific Notation

Physics is a quantitative science, which means that every meaningful statement about the natural world must eventually be tied to a number and a unit. A measurement without a unit is almost useless: saying that a rod is "2 long" tells us nothing, but saying it is $2\ \text{m}$ long communicates a precise physical quantity. To make measurements comparable across the world, scientists use the International System of Units (SI).

Fundamental (base) quantities

The SI system is built on seven base quantities, each with its own base unit. For IB Physics, the ones you must know thoroughly are:

• Mass — kilogram ($\text{kg}$)
• Length — meter ($\text{m}$)
• Time — second ($\text{s}$)
• Electric current — ampere ($\text{A}$)
• Temperature — kelvin ($\text{K}$)
• Amount of substance — mole ($\text{mol}$)

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