Swimming Science

Last week I introduced the idea of sports being grounded by a variety of different scientific principals. When I was younger, I was a swimmer and diver so these water sports hold a special place in my heart. I had NO idea that there was actually science involved in these sports until I was in my 30's and training for a triathlon. How could I have been on a swim team for 4 years and not understand drag or stroke mechanics?! The truth is, I DID understand these things, and my coaches sure as heck ingrained "proper form,"  I just didn't realize that I was doing science when I was perfecting my "catch and pull" motions!  Understanding the scientific principles behind these fun aquatic activities not only enhances performance but also fosters a deeper appreciation for the sports. Check out our Science of Sports Activity Bundle to learn more about all the scientific concepts involved in sports. Now, let's dive into (pun intended) the scientific principals underpinning swimming and diving:

Propulsion and Stroke Mechanics

Propulsion in swimming is primarily achieved through the arms and legs. Different strokes—freestyle, backstroke, breaststroke, and butterfly—utilize distinct mechanics to generate thrust.

Freestyle (Front Crawl)

Propulsion: In freestyle, propulsion is primarily generated by the arms. The stroke cycle involves a "catch," "pull," "push," and "recovery" phase.

• Catch: The hand enters the water in front of the head, fingers first, and extends forward.
• Pull: The hand moves downward and outward, with the elbow higher than the hand, forming an S-shaped curve.
• Push: The hand moves past the hips, pushing water backward.
• Recovery: The arm exits the water and swings forward in a relaxed manner to re-enter and begin the next cycle.

The legs perform a flutter kick, with alternating up and down movements. The kick starts from the hips, with the knees slightly bent, and the feet are relaxed to minimize resistance. Swimmers maintain a streamlined, horizontal position. The head stays low in the water, and the body rotates slightly along the longitudinal axis to aid arm recovery and reduce drag. Breathing occurs during the recovery phase. Swimmers turn their heads to the side, taking a breath without lifting the head too high, which helps maintain body position and minimize drag.

Backstroke

Propulsion: Similar to freestyle but performed on the back, backstroke involves a continuous arm movement with alternating strokes.

• Catch: The hand enters the water above the head, little finger first.
• Pull: The hand sweeps down and outward, with a high elbow position.
• Push: The hand moves past the hips, pushing water backward.
• Recovery: The arm exits the water thumb-first and swings overhead to re-enter and start the next cycle.

The legs perform a flutter kick, similar to freestyle, but with the swimmer on their back.

Swimmers maintain a horizontal position with the face above the water. The body rotates along the longitudinal axis, aiding arm movement and reducing drag.

Breaststroke

Propulsion: Breaststroke involves a simultaneous arm and leg movement.

• Arm Stroke: The hands start together in front of the chest, then sweep outward, downward, and inward, forming a heart-shaped motion. The arms recover forward under the water.
• Kick: The legs perform a frog kick, where the feet move outward and backward in a circular motion, then come together in a streamlined position.

The body remains more horizontal during the glide phase and slightly rises during the stroke to allow breathing. The head and shoulders lift out of the water to breathe. Swimmers inhale during the insweep of the arm stroke when the head is lifted out of the water and exhale during the glide phase when the face is submerged.

Butterfly

Propulsion: Butterfly stroke is characterized by powerful, synchronous movements of the arms and legs.

• Arm Stroke: Both arms move together. The stroke cycle includes a catch phase with hands entering the water shoulder-width apart, a pull phase with hands moving in an hourglass shape under the body, and a recovery phase where the arms swing forward out of the water.
• Kick: The legs perform a dolphin kick, where the feet stay together and move up and down in a wave-like motion. Each arm stroke is accompanied by two kicks.

Swimmers maintain a horizontal, wave-like motion. The body undulates, with the chest pressing down and the hips rising, aiding the dolphin kick. Breathing occurs during the recovery phase. Swimmers lift their heads forward to take a breath as their arms recover forward. Timing is crucial to maintain rhythm and minimize drag.

Diving and Physics

Diving, while seemingly graceful and artistic, is deeply rooted in physics. The principles of projectile motion and rotational dynamics are particularly relevant.

Projectile Motion: When divers leave the platform or springboard, they become projectiles. The trajectory of their dive is influenced by the initial velocity, angle of takeoff, and gravitational force. Divers must carefully control these factors to execute precise entries into the water.

Let's break it down into simple steps:

• Jumping: When you the diver leavers the platform they jump, with a specific force, that pushes them  forward and up into the air.
• Going Up: As the diver goes up, they slow down because gravity (the force that pulls everything down to the ground) is pulling them back down.
• At the Top: The diver reaches a point where they stop going up and starts coming back down. This is the highest point of their path.
• Coming Down: After reaching the top, the diver starts to fall back to the ground. Gravity makes them speed up as it comes down.
• Hitting the water: Finally, the diver enters the water where they break the surface tension of the water and then the water exerts drag on them to slow them to a stop.
  

Rotational Dynamics: Divers perform complex spins and twists during their descent. The speed and number of rotations are governed by the principles of angular momentum. By tucking their bodies tightly, divers decrease their moment of inertia and spin faster. Conversely, extending their bodies slows their rotation. This is why "pike" position where the legs are straight is often more impressive than a "tuck" because the force required to rotate is much greater when the body is longer and causing more air resistance.

The final phase of a dive, water entry, is critical for scoring and safety. Divers aim to minimize splash upon entry, which requires an understanding of fluid mechanics. A clean entry is achieved by aligning the body vertically, pointing the toes, and entering the water with minimal surface area to reduce impact.