Unit of Mass – Class 11 | Chapter – 2 | Physics Short Notes Series PDF for NEET & JEE
Unit of Mass: Mass is a fundamental physical quantity that measures the amount of matter in an object or a substance. It is a scalar quantity, which means that it only has magnitude and no direction. The standard unit of mass in the International System of Units (SI) is kilogram (kg). Mass can be measured using a balance, which compares the object or substance’s mass with known masses. The measurement of mass is an essential aspect of many scientific disciplines, including physics, chemistry, engineering, and biology.
SI Unit of Mass
The SI unit of mass is the kilogram (kg). It is defined as the mass of the International Prototype of the Kilogram (IPK), which is a platinum-iridium cylinder kept at the International Bureau of Weights and Measures (BIPM) in France.
The kilogram is the base unit of mass in the International System of Units (SI). Other units of mass in the SI system are derived from the kilogram, such as gram (g) and milligram (mg).
The kilogram is widely used in science, industry, and everyday life for measuring the mass of objects or substances. It’s important to note that the definition of the kilogram was recently updated in 2019, where it is now defined in terms of the Planck constant, a fundamental constant of nature.
Other Unit of Mass
There are various other units of mass that can be used for measurement. The other accepted units of mass are:
- Gram (g) and its multiples and submultiples
- Tonne (t) or metric ton
- Electron volt (eV)
- Atomic Mass Unit (AMU) (Most convenient for denoting the masses of atoms and molecules.)
Other common units of mass are as follows:
| Common Units of Mass | |
|---|---|
| Milligram (mg) | 0.001 gram or 1/1000 gram |
| Centigram (cg) | 0.01 gram or 1/100 gram |
| Decigram (dg) | 0.1 gram or 1/10 gram |
| Gram (g) | 1,000 milligrams |
| Decagram (dag) | 10 grams |
| Hectogram (hg) | 100 grams |
| Kilogram (kg) | 1,000 grams |
| Metric ton (t) | 1,000 kilograms |
Atomic Mass Unit
The atomic mass unit (amu) is a unit of mass commonly used in chemistry and physics to express the mass of atoms, molecules, and subatomic particles. One atomic mass unit is defined as one-twelfth (1/12) of the mass of a carbon-12 atom, which is approximately 1.66 x 10-27 kilograms.
The atomic mass unit is a convenient unit of mass for expressing atomic and molecular masses because it allows for easy comparison of the relative masses of different atoms and molecules. The mass of an atom or molecule is usually expressed in terms of the atomic mass unit or its multiples, such as kiloatomic mass unit (kamu) and megatomic mass unit (Mamu).
It’s important to note that the atomic mass unit is not equivalent to the unit of mass used in the International System of Units (SI), which is the kilogram (kg). The atomic mass unit is a more specific unit that is only used in the context of atomic and molecular masses.
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