Kilogram

Definition

A kilogram is the base unit of mass in the International System of Units (SI). It is defined by the mass of the International Prototype Kilogram, a platinum-iridium alloy cylinder kept at the International Bureau of Weights and Measures.

5 Must Know Facts For Your Next Test

1. The kilogram is one of the seven base units in the SI system.
2. Originally defined as the mass of one liter of water at its freezing point, it is now defined by physical constants including Planck's constant.
3. The symbol for kilogram is 'kg'.
4. It was redefined in 2019 to be based on fundamental physical constants rather than a physical object.
5. 1 kilogram equals 1000 grams.

Review Questions

• What is the current definition of a kilogram based on?
• How many grams are there in a kilogram?
• What was used to define a kilogram before it was redefined in 2019?

Related terms

Gram: A unit of mass equal to $\frac{1}{1000}$th of a kilogram.

International Prototype Kilogram: A platinum-iridium alloy cylinder that was historically used as the standard for defining one kilogram.

Planck's Constant: $6.62607015 \times 10^{-34}$ Js, a fundamental constant used in the modern definition of the kilogram.