Part 1: Newton's Second Law
In this picture, Olympic and world best tennis player, Serena Williams, hits the tennis ball during a match at the US Open in New York. A person can see that Serena has a racquet in her hand and that the ball is going away from her because she just exerted a force on the ball. This makes the ball go over the net and land in her opponents court. A physics concept that is being used in this picture is Newton's Second Law. Newton's Second law states that acceleration is directly proportional to the net force on an object and is inversely proportional to the mass of the object. When a tennis racquet hits a ball, Newton's Second Law determines the acceleration of the ball due to the force of the racquet acting on it. This means the harder a player hits the ball, the faster it will go. A player used Newton's Second Law in two different ways. One is with gravity and one is when the racquet hits the ball. With gravity, the force that it puts on an object will depend on the mass of the object and the acceleration would stay the same. Since a person now knows the mass and the acceleration due to gravity, the person can then calculate the force due to gravity. When the ball comes in contact with the racquet, the racquet then causes the ball to accelerate by applying a force to it.