Thank for the answer, but can you explain the definition of "dimensional" quantities. I don't know why people say dimension of time, dimension of mass, etc. Does dimensional quantities have any relation to those. Also, how do we know there are dimensionless value (not unit/quantities). For example, some constants in physical equation.

ocw.mit.edu/courses/physics/… In this clip, in the Galieo section he mention about how to make an equation that express the time when a thing drop at a certain length h. He associate Mass, time, length to create the equation but I don't know how how he know what quantity should be add into an equation.