Physics of Swimming

Common Strokes for Swimming

There are four common strokes associated with swimming: butterfly, backstroke, breaststroke, and crawl stroke. Breaststroke and backstroke are considered ‘rest’ strokes; crawl stroke, also known as freestyle, and butterfly are known as ‘power’ strokes. A rest stroke uses less energy to travel the same distance, however; it takes longer to achieve this distance. A power stroke uses more energy and covers greater distances in less time.

The sidestroke and elementary-backstroke are two more rest strokes used in swimming. Each of these are not used competitively, but instead are taught to beginners to help them understand all aspects of swimming.

Each stroke is unique in body position and the method used to propel each body differs for every stroke.

Body Position and Physics

While swimming, it is important to realize what each body part is doing and where it is moving.

The push-off: While pushing off the wall, the body should be submerged and facing the bottom of the pool. The hands should be together and stretched out in front. The biceps, pressed against the ears, head stationary and perpendicular to the body. The swimmer should be flat and streamline in the water, with the feet swept back. The push-off is the same for all the strokes, except the backstroke. In this situation, the body is instead facing the ceiling of the pool.

Physics: As the body assumes a streamline position and is forced off the wall, the sleeker the body, the less drag produced. If any of the characteristics listed above change, a greater drag-force is applied to the body, thus slowing the swimmer down.

When the body begins to loose speed and float to the surface, the kick and first stroke is applied. The kick helps propel the body through the water, while the stoke helps pull it.

The stroke: Each stroke and pattern is unique. The crawl stroke uses a flutter kick and an ‘S’ stroke to propel the body. The butterfly uses the dolphin kick and a ‘key-hole’ stroke. The back uses the same flutter kick as the crawl, but uses an out-sweep 'L' stroke. The breaststroke uses the breaststroke kick and a scooping motion for its pull.

Physics: Each stroke has a catch, power phase, and recovery. The physics of each stroke is similar so only the freestyle will be explained and the others will be related to it.

Freestyle begins with the catch, a motion which allows the swimmer's hand to engage the water.