What's the plural form of inertial mass? Here's the word you're looking for.
Answer
The noun inertial mass can be countable or uncountable.
In more general, commonly used, contexts, the plural form will also be inertial mass.
However, in more specific contexts, the plural form can also be inertial masses e.g. in reference to various types of inertial masses
or a collection of inertial masses.