The Physics of Swimming: Increasing Efficiency in the Water Using Newton's Third Law of Motion

As a member of the Swim team at Colgate, I spend 20 hours a week swimming laps in the 25 yard pool. My Coach, Ed Pretre, always reminds us that our efficiency is more important than the effort we are putting in (but the effort we are putting in is still very important.) This may sound like he is telling us it is okay to not work hard. However, that is not the case; he is telling us it is more important to swim smart, and swimming smart starts by analyzing Newton’s third law of motion, which can help maximize efficiency in the water, and allow us to excel against our competitors. 

Newton’s third law of motion states that, “whenever one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first.” The textbook gives the example of an ice skater pushing against a wall, and the wall pushing back on the skater. The force between these two objects results in the skater accelerating away from the wall.

The same concept can be applied to swimming, when swimmers do flip turns. Flip turns are when the swimmer reaches the wall, does a “somersault,” which orients the swimmer in a way that will allow them to plant their feet on the wall, shoulder-width apart (Figure 1). The swimmer is then ready to “push” off the wall using their legs, and this acceleration from the wall is used to help the swimmer gain speed as they continue their race.                   

In order to push off the wall with the highest acceleration the swimmer can possibly achieve, the swimmer must increase speed as he or she approaches the wall. The more force the swimmer can generate when they push off the wall, the more acceleration the swimmer will be able to attain coming off the wall. The swimmers who swim towards the wall at a higher speed are the ones who have the most acceleration coming off the wall, which will drive the swimmer ahead of his or her competitors who are not using physics to maximize their efficiency in the water. 

The fastest swimmers are the ones who are able to pull the most water, and pull this water at a faster rate than their competitors. The amount of water a swimmer is able to pull is dependent both the strength of the swimmer, and on the angle at which the elbow is bent when it is directly underneath the shoulder. Ideally, this angle should be 90 degrees, as this is the angle at which the surface tension between the water and the swimmers arm is the highest, allowing the swimmer to propel themselves further in the water.