Answer to Question #4719 in Physics for ababiya

Question #4719
describe the difference between fundamental and derived physical quantities
Expert's answer
The fundamental quantities:
* Time
* Space (or length)
* Mass
* Temperature
* Electrical current
* Luminosity
* Amount of matter

Each fundamental quantity has an associated unit in the SI system:
* Time: seconds (s)
* Space: meters (m)
* Mass: kilograms (kg)
* Temperature: degrees Kelvin (K)
* Electrical current: ampere (A)
* Luminosity: candela (l)
* Amount of matter: mole


Time is perhaps the most abstract of the fundamental quantities, possibly because we experience it in a linear way; we can't get out of it. Space can be experience from a nonlinear perspective, and is more easily grasped as a distinct concept. The same goes for mass, which is very tangible. Temperature is experiential but its quantum definition veers into abstract territory (in simplistic terms, it is the amount of atomic vibration in a system). Like temperature, electrical current is an everyday experience, but gets stranger the more closely it is analyzed (the "flow" of electrons through a medium). Luminosity is straightforward (we can see how it changes). The mole is a stumbling block for students of chemistry, but ultimately makes sense as a measurement of items (particularly of matter).

Derived Quantities

All other quantities in physics can be expressed in terms of the fundamental quantities. Examples are velocity (space divided by time), acceleration (space divided by time squared), force (mass times space divided by time squared) or energy (mass times the constant representing the speed of light squared - aka. space divided by time all squared). Understanding this concept helps in understanding how all equations work, and how different "things" are related. In teaching physics this is an important concept to transfer - teaching students not just to work an equation, but really understand it in terms of how derived quantities relate to fundamental quantities.

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