Using commas for lists containing independent clauses

'To be clear' is a pragmatic marker (in this case one indicating clarifying specification in the matrix sentence), syntactically apart from the matrix sentence, and this setting off needs some separator. Introductory pragmatic markers (and there are many types), whether single- or multi-word, are usually set off by commas.

While semicolons could be used to separate main clauses (and are really needed in many cases – see 'comma splices' in other threads here), they are usually too heavy-duty between listed main clauses, as here. Also, more than one semicolon in a sentence is not normal, and a semicolon before 'and' is unusual.

However, the different roles of the first (parenthetical offsetting) comma and the other commas here clashes somewhat. I'd use:

• To be clear: a is the acceleration of the object, F is the net force on the object, and m is the mass of the object.