newton's third law of motion?

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ok so Whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction.

so When I sit on a chair, I am exerting an equal force on the chair as the chair is exerting on me, Right?

what if I get up and push the Chair? are the Forces still equal then? because I am a First Body exerting a force on a Second body... but if it's equal how come the Chair moves?

Thanks