SI units

Definition

SI units are the internationally accepted system of measurement used in science and engineering. They provide a standardized way to quantify physical quantities.

5 Must Know Facts For Your Next Test

1. The SI unit system is also known as the International System of Units.
2. There are seven base SI units: meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd).
3. Derived units in the SI system are formed by combining base units according to algebraic relationships.
4. The meter is defined based on the speed of light, while the kilogram is defined by the Planck constant.
5. SI prefixes like kilo- ($10^3$) and milli- ($10^{-3}$) are used to express multiples and submultiples of SI units.

Review Questions

• What are the seven base units in the SI system?
• How is the meter currently defined in terms of physical constants?
• Give an example of a derived unit in the SI system.

Related terms

Meter: The base unit of length in the SI system, defined by the distance light travels in a vacuum in $1/299,792,458$ seconds.

Kilogram: The base unit of mass in the SI system, defined by setting the Planck constant exactly equal to $6.62607015 \times 10^{-34}$ joule seconds.

Derived Unit: A unit that is derived from one or more base units through algebraic relationships, such as meters per second for velocity.