# Is displacement vector fundamental or derived quantity?

We know that we have 7 fundamental quantities (all scalars) and length is one of them. I classify velocity as a derived quantity. What about a position displacement vector? How do I classify displacement vector. Is it fundamental or derived quantity?

## 1 Answer

It depends on the convention what to use as a fundamental quantity, but if you refer to SI it is:

$$[D] = [\epsilon_0]\cdot [E] = [\epsilon_0]\cdot [F]/[Q] = \mathrm{\frac{A^2\, s^4}{kg\, m^3}\cdot \frac{kg\, m}{s^2}\cdot \left(A\, s\right)^{-1} = \frac{A\, s}{m^2}}.$$

• a fundamental quantity if you refer to a position displacement, because it is a length,

$$[r] = \mathrm m.$$

• I am referring to a position displacement. Because I asked a question because I saw a question asking 7 fundamental quantities are scalars or vectors. The answer was scalar. So I was a little bit confused that position displacement is a vector not scalar. – ofenerci Oct 3 '17 at 10:19
• Could you link the question you have just cited? @ofenerci – Annibale Oct 3 '17 at 15:01
• Length is a scalar coming from this post physics.stackexchange.com/questions/67375/… – ofenerci Oct 3 '17 at 15:55