Physics

Forces, Energy and Electricity

# Physical Quantities

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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.