Newton's Laws of Motion
Law #1 (The Law of Inertia)
Newton's first law states that an object in motion will tend to stay in motion unless acted upon by an outside force. This means that if you throw a lacrosse ball in a straight line it will continue moving in a straight line until it is acted upon by gravity or another player's stick. So if you throw a lacrosse ball in a straight line it starts to go down because gravity is constantly acting upon it.
Newton's second law states that force can be calculated by multiplying the acceleration of the object by the mass of the object. For example in lacrosse, if an attacker was to take a shot and hit a defender with that shot it would hurt. But say you wanted to find the force of that impact. Newton's second law says that you could determine the force of the impact by multiplying the acceleration of the shot (20 m/s squared) by the mass of the ball (140g or 0.14kg). Therefore, the force would be 2.8 Newtons.
Newton's third law states that every action has an equal and opposite reaction. In lacrosse, this could be used to analyze a body check. Say a lacrosse player gets hit with 4 Newtons of force. This would mean that while the checking player is dishing out 4 Newtons of force to the other player, he is taking that much force to his body as well.