Newton's first law of motion - sometimes referred to as the law of inertia. An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. Here, the pins are at rest, until they are acted upon by an unbalanced force, or a bowling ball.
Newton's second law of motion can be formally stated as follows: The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. Gravity affects the way the bowling ball moves through the air as you throw it and it how fast it goes down the lane.
Newton's third law is: For every action, there is an equal and opposite reaction. The action is a person throwing the bowling ball down the ally. The equal and opposite reaction is the ball rolling down the ally and knocking down all of the pins in the balls path.