Physical Quantities
Physical Quantities
Basic Definitions
- Physical quantities are measurable properties or qualities of a physical system.
- Physical quantities are described by a numerical magnitude and a unit. They are broadly classified into two types: Scalar and Vector quantities.
- Scalar quantities only have magnitude, for example time, speed and mass.
- Vector quantities have both magnitude and direction, such as force, velocity, and displacement.
Scalar Quantities
- Scalar quantities are completely specified by their magnitude alone.
- Magnitudes are always positive and can be added, subtracted, multiplied, or divided like ordinary numbers.
- Speed, energy, and power are some examples of scalar quantities.
Vector Quantities
- Vector quantities are described by both magnitude and direction.
- The vector sum or resultant of multiple vectors is found using the rules of vector addition.
- Examples of vector quantities include force, velocity, acceleration, and momentum.
Units of Measurement
- Units are standard quantities used to specify the magnitude of a physical quantity.
- The International System of Units (SI) is a globally agreed system of measurements that includes seven base units: metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol) and candela (cd).
- Derived units are combinations of base units, for example, force is measured in newtons (N), which are equivalent to kg m/s².
Dimensional Analysis
- Dimensional analysis checks the validity of an equation by comparing the dimensions on both sides.
- It helps in converting units from one system to another and in deriving relationships between different physical quantities.
Uncertainty and Significant Figures
- Measurements always have some uncertainty, which is expressed in terms of error.
- The reported value of a measurement should only include digits that are known with certainty, plus the first uncertain digit. These digits are known as significant figures.
- When multiplying or dividing measurements, the final result should retain the smallest number of significant figures used in the calculation.