Newton's Second Law

"The acceleration of an object is proportional to the force and inversely proportional to the mass acting on it.."

How this pertains to Bowling

Simply put, the greater the acceleration of the ball when its hits the pins, the harder you hit and the further they fly. Also the mass of the ball and velocity determines the momentum of the hit.  If you were using an 8 lb. ball you wouldn't have nearly as much force as if you were using a 16 lb. ball.