Physical Quantities in Physics

Physical Quantities

• Physical quantities are measurable quantities used to describe the laws of physics.
• Examples include length, velocity, acceleration, force, time, pressure, mass, and density.
• Physical quantities are categorized into three types: fundamental, derived, and supplementary.

Fundamental (Basic) Quantities

• These are elementary quantities that are independent from each other.
• Any other physical quantity can be derived from these basic quantities.
• Seven fundamental quantities were chosen by the General Conference on Weights and Measures(CGPM): length, mass, time, temperature, electric current, luminous intensity, and amount of substance.

Derived Quantities

• Derived quantities are expressed in terms of fundamental quantities.
• Examples include area, velocity, acceleration, force, momentum, work, energy, power, and pressure.

Supplementary Quantities

• There are two supplementary quantities: plane angle and solid angle.

Dimensions of Physical Quantities

• The dimension of a physical quantity represents the powers of fundamental quantities.
• The dimension of length is [L], mass is [M], time is [T], and so on.
• The dimension of a derived quantity is found by combining the dimensions of the fundamental quantities that define it.

Dimensions of Physical Constants

• Physical constants, like the gravitational constant and the speed of light, also have dimensions.
• Determining the dimensions of physical constants allows for checking the dimensional consistency of equations.

Limitations of Dimensional Analysis

• Dimensional analysis is useful for checking if an equation is dimensionally correct but it cannot determine the numerical value of the constant of proportionality.
• Dimensional analysis is limited to quantities where the relationship between variables is through multiplication and powers as it cannot handle trigonometric, logarithmic, or exponential relationships.
• It only works if the quantity depends on no more than three independent variables.

Converting Units

• Conversion between different units involves multiplying the numerical value by a conversion factor.
• The magnitude of a physical quantity remains constant when changing units

SI Derived Units

• Some SI derived units have names based on scientists who made significant contributions to the field of physics.