UNITS AND DIMENSIONS (PART-1)
Basic Introduction
PHYSICAL QUANTITIES
All quantities that can be measured are called physical quantities. E.g. time, length, mass,
force, work done, etc. In physics we study about physical quantities and their inter
relationships.
MEASUREMENT
Measurement is the comparison of a quantity with a standard of the same physical quantity.
Different countries followed different standards
UNITS
All physical quantities are measured with respect to standard magnitude of the same physical
quantity and these standards are called UNITS. e.g. second, meter, kilogram, etc.
Four basic properties of units are:
1. They must be well defined.
2. They should be easily available and reproducible.
3. They should be invariable e.g. step as a unit of length is not invariable.
4. They should be accepted to all.
Set of Fundamental Quantities
A set of physical quantities which are completely independent of each other but all other
physical quantities can be expressed in terms of these physical quantities is called Set of
Fundamental Quantities.
The Fundamental Quantities that are currently being accepted by the scientific community are
mass, time, length, current, temperature, luminous intensity and amount of substance.
Derived Physical Quantities
The physical quantities that can be expressed in terms of fundamental physical quantities are
called derived physical quantities. E.g. speed = distance/time.
System of Units
1. FPS or British Engineering system: In this system length, mass and time are taken as
fundamental quantities and their base units are foot (ft), pound (lb) and second (s)
respectively.
Basic Introduction
PHYSICAL QUANTITIES
All quantities that can be measured are called physical quantities. E.g. time, length, mass,
force, work done, etc. In physics we study about physical quantities and their inter
relationships.
MEASUREMENT
Measurement is the comparison of a quantity with a standard of the same physical quantity.
Different countries followed different standards
UNITS
All physical quantities are measured with respect to standard magnitude of the same physical
quantity and these standards are called UNITS. e.g. second, meter, kilogram, etc.
Four basic properties of units are:
1. They must be well defined.
2. They should be easily available and reproducible.
3. They should be invariable e.g. step as a unit of length is not invariable.
4. They should be accepted to all.
Set of Fundamental Quantities
A set of physical quantities which are completely independent of each other but all other
physical quantities can be expressed in terms of these physical quantities is called Set of
Fundamental Quantities.
The Fundamental Quantities that are currently being accepted by the scientific community are
mass, time, length, current, temperature, luminous intensity and amount of substance.
Derived Physical Quantities
The physical quantities that can be expressed in terms of fundamental physical quantities are
called derived physical quantities. E.g. speed = distance/time.
System of Units
1. FPS or British Engineering system: In this system length, mass and time are taken as
fundamental quantities and their base units are foot (ft), pound (lb) and second (s)
respectively.
