A-level Mathematics/M1/Newton's Laws of Motion

Newton's first law of motion states that a body acted on by a balanced set of forces will stay at rest if it is at rest, and it will continue at a constant velocity if it is in motion. A common phrasing of the law is if the body is acted on by external forces however this is incorrect, for example a car can be acted on by no external forces and it can accelerate.

Newton's second law of motion states that if a body is acted on by an unbalanced set of forces then the resultant force equals the mass of the object times the acceleration of the object: $F=ma$

Newton's third law of motion states that every force has an equal and opposite reaction force.