Kilogram

Definition

A kilogram is the base unit of mass in the International System of Units (SI). It is defined by taking the fixed numerical value of the Planck constant, $h$, to be $6.62607015 \times 10^{-34}$ when expressed in units of $\text{kg} \cdot \text{m}^2 / \text{s}$.

5 Must Know Facts For Your Next Test

1. The kilogram is the only SI base unit with a prefix (kilo) as part of its name.
2. The definition of a kilogram was redefined in 2019 based on fundamental physical constants, specifically the Planck constant.
3. One kilogram is approximately equal to 2.20462 pounds.
4. Kilograms are used worldwide for measuring body weight, food items, and various other everyday objects.
5. In scientific contexts, kilograms are often used to measure quantities such as force and energy through derived units like newtons and joules.

Review Questions

• What fundamental physical constant is used to define a kilogram?
• How does the current definition of a kilogram differ from its historical definition?
• What are some common everyday items that are typically measured in kilograms?

Related terms

Gram: A gram is a unit of mass equal to one-thousandth of a kilogram.

Newton:

A newton is the SI unit of force equivalent to one kilogram meter per second squared ($\text{N} = \text{kg} \cdot \text{m/s}^2$).

Joule:

$$A joule is the SI unit of energy equal to one newton meter ($\text{J} = \text{N} \cdot \text{m}$)$$.