The International System of Units

Is the modern form of the metric system.

physical quantities

quantities that can be measured

Fundamental quantities

basic quantities which are independent of one another

derived quantities

quantities that are calculated from two or more measurements.

Conversion of units

The simplest way to convert one unit to another is to form a conversion ratio with the desired unit on the numerator and the unit to be converted at the denominator.

Random Errors and Systematic Errors

Two types of errors

random error

This results from unpredictable or inevitable changes during data measurement

Systematic errors

This usually come from the measuring instrument or in the design of the experiment itself.


Refers to the closeness of a measured value to the expected or true value of a physical quantity


Represents consistent independent measurements of the same quantity are to one another


Indicates the range of value within which the measurement is asserted to lie with some level of confidence

Absolute uncertainty and relative uncertainty

Types of uncertainty

absolute uncertainty

Usually based on the least count of the measuring device

relative uncertainty

A dimensionless and is obtained by dividing the absolute uncertainty by the numerical or measured value

Classical physics, modern physics, nuclear physics, atomic physics, geophysics, biophysics, thermodynamics, astrophysics, acoustics, optics, mechanics

Branches of Physics