Newton's First Law


Newton’s first law states that an object remains at rest or in motion unless acted on by a force. Thus, a swimmer remains at rest or moves in constant velocity unless acted on by a force. Water has resistive and propulsive forces, and in order for a swimmer to be in motion the propulsive forces must be greater than the resistive forces.


Newton's Second Law

Newton’s second law states that the sum of the forces of an object must be equal to the object’s mass times its acceleration. There are many different forces acting upon every part of a swimmer’s body, the arms, legs, and head. To simplify it, we will look at the swimmer as a whole by focusing on the center of mass of the swimmer. By doing this, we can look at the following free body diagram which gives all the forces that act on a swimmer. The propulsive force acts in the direction of motion propelling the swimmer forward, while the resistive force opposes the direction of motion having the same effect as a friction force by slowing down the swimmer. B stands for the buoyancy force, which acts upward from the water. The buoyancy force is equal to W, which is the force of gravity acting downwards. The force of gravity is equal to the mass of the swimmer times the gravity constant which is approximately 9.81 m/s^2. Since the swimmer is only moving in the horizontal direction, F(net) = propulsive force – resistive force.








 
































Photo from indiana.edu




Newton's Third Law

 

Newton’s third law states that every action must have an equal and opposite reaction. In swimming, when the hands and feet push against the water, the water pushes back on the swimmer and propels the swimmer forwards.