[Physics] Standard Usage of the word “per”

conventionsnotation

Math guy here. What is the usual meaning of "x per y per z?" Is this (ignoring details) (x/y)/z or x/(y/z)?

Sorry to be mundane.

Best Answer

Two examples that come to my mind are acceleration and intensity.

Acceleration is measured (in SI units) in "meters per second squared" = $\text{m}/\text{s}^2$, but it is also commonly said as "meters per second per second," which matches your first option.

Likewise, intensity is measured (in SI units) in "joules per square meter per second" = $\text{J}/(\text{m}^2\text{s})$, which also matches your first option.

I can't claim this is always the case, but I would guess most of the time it is.