# What does “dimension” mean in physics? [closed]

Still I don't get what's the difference between dimension and quantity. Are they same or they are different?

## closed as unclear what you're asking by AccidentalFourierTransform, John Rennie, Jon Custer, Cosmas Zachos, rob♦Feb 18 '17 at 2:16

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• Just to clarify: do you basically mean "what's the difference between e.g. 'velocity' (quantity) and 'meters per second' (dimension/unit)"? – jabirali Feb 16 '17 at 18:47

A bit more precisely, you can see nouns like length, velocity, time, and mass as describing abstract quantities, i.e. "a velocity $v$" specifies that $v$ is a velocity but nothing else. Physical dimensionality is, at its heart, an equivalence relationship: in essence, you are always saying "quantity $A$ and quantity $B$ have the same physical dimensionality". Thus all lengths have the same physical dimensionality, and "the distance between New York and Los Angeles" has the same physical dimensionality as any length, which we just describe as 'length' in the abstract.