Teachers and Students in Science, Technology, Engineering and Mathematics
What is the International Systems of Units (SI)
How do you express a value of a quantity?
Number
Unit
For example:
The speed v of a particle may be expressed in the form
v = 25 m/s note
= 90 km/h
note: metre per second and kilometer per hour are alternative units for expressing the same value of quantity of speed
There are many different units for expressing the same quantity
- Length: metre, inch, foot
- Temperature: degree Celsius, degree Fahrenheit, kelvin
- Time: second, minute, hour, week, month, year
- Mass: pound, gram, kilogram, ton
Why use the International System of Units (SI)?
- SI is decimal
- SI is internationally accepted
- SI is a rational system of units
Who establish the SI?
The SI was established by and is defined by the General Conference on Weights and Measures (CGPM). CGPM is made up of delegates of the governments of the Member States and observers from the Associates of the CGPM.
What is the SI?
The SI includes seven base units and many derived units defined as products of powers of the base units. The seven base units were chosen for historical reasons, and are by convention, regarded as dimensionally independent: the metre, the kilogram, the second, the ampere, the kelvin, the mole and the candela.