KOW January 20, 2020

This week's KOW takes a closer look at the physics of swimming based on Newton's 3 Laws of Motion. Here is the video.

The initial search for scientific principles and their application to swimming propulsion began in the middle 20th century and ended with Newton's Three Laws of Motion. Other propulsive theories have been presented recently but the most compelling choice is still Newtons. 

Simply stated, those laws are; 
  • First, every object in a state of uniform motion will remain in that state unless an external force acts upon it. 
  • Second, force equals mass times acceleration. 
  • And Third, for every action there is an equal and opposite reaction.
In swimming, the importance of Newton's laws are best viewed in reverse order. Newton's third law tells us that we push against the water and the water pushes us back. 

Wouldn't it be great if we really could pull and push water? Our sport would be much easier if we installed 75 ft long ladders, about 2 feet below the surface, extending from wall to wall, with the rungs separated by the wingspan of your arms.  You can shove off the wall, grab the rungs and just pull and push to propel yourself forwards. 



This is a perfect yet unattainable goal because water is a liquid not a solid. 

We can treat it like a solid by applying Newton's Second Law in more force. Increased force equals increased propulsion. There are a number of ways to increase force:
  • you can make your hands and limbs firmer.
  • you can apply pressure against the water longer.
  • you can reach deeper into the water, 
  • and most importantly, you can accelerate each motion start to finish. 

And last, Newton's First Law tells us that objects at rest tend to remain at rest until acted upon by an outside force.)