Asked by ABAINEH
Why is fundamental physical quantities different from derived physical quantities
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Short answer
Fundamental (or base) physical quantities are a small set of independent quantities chosen as the basic building blocks for measurement (for example length, mass, time in the SI system). Derived quantities are any other quantities that can be expressed algebraically from those base quantities (for example speed = length/time, force = mass × length / time^2).
Why they are different — key points
- Independence vs dependence: Base quantities are taken as independent primitives — you cannot express them in terms of one another. Derived quantities depend on the base ones and can be written as products/powers of base quantities.
- Role in units: Each base quantity has its own base unit (meter, kilogram, second in SI). Derived quantities have units that are combinations of base units (m/s for speed, N = kg·m/s^2 for force).
- Practical choice and convention: Which quantities are chosen as “base” is partly a convention for convenience and reproducibility. The SI system uses seven base quantities (length, mass, time, electric current, thermodynamic temperature, amount of substance, luminous intensity).
- Usefulness: This separation makes unit systems coherent, simplifies dimensional analysis, and helps check equations for consistency by comparing dimensions.
Examples
- Base: length (L), mass (M), time (T).
- Derived: area = L^2; speed = L T^−1; acceleration = L T^−2; force = M L T^−2; energy = M L^2 T^−2.
A short caveat
Sometimes “fundamental” is used in different senses (e.g., fundamental physical constants like the speed of light c or Planck’s constant h). Also different unit systems may pick different base sets — the distinction is a practical classification, not a deep physical law.
Fundamental (or base) physical quantities are a small set of independent quantities chosen as the basic building blocks for measurement (for example length, mass, time in the SI system). Derived quantities are any other quantities that can be expressed algebraically from those base quantities (for example speed = length/time, force = mass × length / time^2).
Why they are different — key points
- Independence vs dependence: Base quantities are taken as independent primitives — you cannot express them in terms of one another. Derived quantities depend on the base ones and can be written as products/powers of base quantities.
- Role in units: Each base quantity has its own base unit (meter, kilogram, second in SI). Derived quantities have units that are combinations of base units (m/s for speed, N = kg·m/s^2 for force).
- Practical choice and convention: Which quantities are chosen as “base” is partly a convention for convenience and reproducibility. The SI system uses seven base quantities (length, mass, time, electric current, thermodynamic temperature, amount of substance, luminous intensity).
- Usefulness: This separation makes unit systems coherent, simplifies dimensional analysis, and helps check equations for consistency by comparing dimensions.
Examples
- Base: length (L), mass (M), time (T).
- Derived: area = L^2; speed = L T^−1; acceleration = L T^−2; force = M L T^−2; energy = M L^2 T^−2.
A short caveat
Sometimes “fundamental” is used in different senses (e.g., fundamental physical constants like the speed of light c or Planck’s constant h). Also different unit systems may pick different base sets — the distinction is a practical classification, not a deep physical law.
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