[jagrsw]

Technically (physically) it's force (as in SI's F).

[polishdude20]

Oh that makes sense! I'm thinking back to how people say "On jest silny" as in "He is strong" I wouldn't say "He is force"

[jagrsw]

Mind you, you changed 'strength' (noun) to 'strong' (adj) in your example.

"He is forceful" if you insist on playing this game. Another derived adjective if forcible but it has a bit more elusive meaning (forcible entry into a building)