I understand the contraction of “it’s,” but am confused on possession. If I use an object as opposed to a person, how is “it” used? For example, “the force of an object is equal to its mass times its acceleration.” Would it be “it’s” mass and “it’s” acceleration? Wouldn’t it be “Joe’s mass and the wheel’s acceleration?

My son is writing a report and wants it to be perfect.

Dear G:

No. You write “its mass” or “its acceleration.” When you write the possessive of nouns, you do spell the word with an apostrophe to distinguish it from a plural. However, “its” is a personal pronoun, and personal pronouns do not use apostrophes: “his dog” or “that cat is hers.” (We do not write, “hi’s dog,” for example.) It’s the same with “its.”