Physics Behind Swimming

Learn about the physics behind swimming, a great sport.

“If I were dropped out of a plane into the ocean and told the nearest land was a thousand miles away, I’d still swim.  And I’d despise the one who gave up,” were the words of the famous psychologist Abraham Maslow. In this quote, swimming has been used as a metaphor. However, the word, literally, is also correct. Swimming can be fun and it can also save your life under certain circumstances. Swimming has been part of human nature for a long time. Even though it takes a little practise, learning to swim is very easy. Have you ever wondered about the scientific reasons behind swimming? It is a phenomenon and can be described using physics.

When a swimmer kicks and moves his arm through water, he applies a downward force on the water. He also applies some force to the water behind him. By studying Newton’s third law of motion, we know that: “for every action force, there is a reaction force of equal magnitude.” Therefore, when the swimmer applies a downward and backward force on the water, the water also exerts a forward and upward force on the swimmer.  There are also other different types of forces that work when a human body is moving through water. Some of them are: gravity, buoyancy, drag force, and the lift force.

                Firstly, the force of gravity pushes you down towards the water. A person with more mass will have a larger force of gravity working on him. Therefore, it will be harder for him to stop sinking. This force will pull the person down towards the core of the Earth and try to make him sink.

Secondly, buoyancy is the force that pushes objects upwards against the force of gravity in a fluid. Therefore, for a person to float on water the buoyant force has to be greater or equal to or greater than the force of gravity acting on the object. While swimming, buoyant force of water on the object depends on different factors like: surface area of the object, density and the weight of water displaced by the object. Furthermore, the less dense an object is, the more chance that it will float on water. In addition, the more weight of water an object displaces while swimming, the greater the force that pushes back and creates buoyancy. This is why life jackets are used to keep people afloat on water. Life jackets weigh very little. Therefore, it needs to displace very little amount of water to float and it could support the weight of a person.

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