Base Quantities:
Base quantities are the fundamental quantities in physics that are considered independent and cannot be expressed in terms of other quantities. They form the foundation of the measurement system and are defined arbitrarily. The seven base quantities in SI are:
1. Length: Measured in meters (m) and is the fundamental quantity used to measure distances, lengths, and dimensions in space.
2. Mass: Measured in kilograms (kg) and represents the amount of matter in an object. It is used to quantify the inertial and gravitational properties of objects.
3. Time: Measured in seconds (s) and is the fundamental unit of time. It is used to measure the duration of events and processes.
4. Electric Current: Measured in amperes (A) and represents the flow rate of electric charge. It is used to quantify the movement of electric charge in a circuit.
5. Thermodynamic Temperature: Measured in Kelvin (K) and represents the measure of the average kinetic energy of the particles in a substance. It is used to quantify the hotness or coldness of an object.
6. Amount of Substance: Measured in moles (mol) and represents the quantity of matter present in a sample. It is used to quantify the number of particles (atoms, molecules, ions, etc.) present in a substance.
7. Luminous Intensity: Measured in candela (cd) and quantifies the luminous power or brightness of a light source. It is used to measure the intensity of light emitted by a source.
Derived Quantities:
Derived quantities are physical quantities that are expressed in terms of the base quantities through mathematical operations and relationships. They are dependent on and can be derived from the base quantities using mathematical equations, formulas, or definitions. There are countless derived quantities in physics, but here are a few common examples:
1. Speed: Measured in meters per second (m/s) and is a derived quantity calculated by dividing the distance traveled (length) by the time taken (time).
2. Volume: Measured in cubic meters (m^3) and is calculated by multiplying the length, width, and height of a three-dimensional object.
3. Density: Measured in kilograms per cubic meter (kg/m^3) and is calculated by dividing the mass of an object by its volume.
4. Force: Measured in newtons (N) and is a derived quantity expressing the interaction that causes a change in the motion of an object. It is calculated as the product of mass and acceleration.
5. Energy: Measured in joules (J) and is a derived quantity representing the ability to do work. It can be expressed in various forms, such as kinetic energy (energy of motion), potential energy (stored energy), and thermal energy (heat).
6. Power: Measured in watts (W) and is calculated as the rate at which work is done or energy is transferred. It is obtained by dividing the work done by the time taken.
These are just a few examples of derived quantities, and there are numerous others defined based on specific scientific disciplines and applications. The SI system provides a coherent framework for expressing physical quantities using the base quantities and the derived quantities derived from them.
