Question

What is the difference between a physical quantity and dimensions?

Like.. length, mass and time are both physical quantity and dimensions? Then, what's the difference between them?

Answer 1

Physical properties are properties that externally show what the system actually is
That is for example consider a block. The length, temperature, mass etc define how physically the block look.
Now., the basic physical properties are
Mass
Length
Temperature
Time etc.

I understand your question clearly. You want to know what the difference is between a physical quantity and dimensions. A physical quantity can be easily represented as on the basis of a few basic dimension like the ones given above.
For example Area is a physical quantity right? But area is the product of length and length. So it can be written like
A= L^2 ( Read this as L square).
Another example is Speed.
Speed is distance / time.
Distance is expressed on the basis of length L and time on t.
So speed is L t^-1
Similarly we can convert bigger physical quantities on the basis of simple dimensions.
If you work out you will notice that FORCE is
F= MLT^-2

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