Newton’s First Law applies to decreasing resistance for swimming efficiency. In contrast, Newton’s Third Law applies to the other means toward efficiency: increasing propulsion.

Newton’s Third Law is the Law of Action-Reaction: Every action creates an equal and opposite reaction.

The quickest way to use this law is to push off from the pool wall. The action of pushing into the wall creates the reaction of the body moving away from the wall. If the push is easy, the swimmer gets a weaker start than with a harder push (opposite but equal).

There are other ways that Newton’s Third Law can work either for or against a swimmer. A swimmer who starts stroking with arm and hand at the water’s surface will create a downward force on the water, which will move the body up (opposite) rather than forward.

The swimmer needs to direct force toward the feet in order to propel the body toward the head and beyond.

This is best accomplished, as many of my columns have urged, by being sure that the hand is always below the elbow. Thus, not only the hand, but the insides of both the lower arm and upper arm are able to push backwards against non-moving water so that the body moves forward. The higher the elbow and the earlier it is rotated or lifted into position, the more backwards effort is possible.

While this is true with the swimmer’s arms for all strokes (see Jan. 15 column), it is also true for leveraging the legs in the breaststroke.

The breaststroke kick is most effective when the lower legs rotate around the knees. This “whip kick” action enables the swimmer to push backwards with the bottoms of the feet and also with the insides of the lower legs.

Newton’s Third Law, along with the First, also tells the swimmer what not to do. If the swimmer keeps elbows down, not only is momentum impeded by frontal resistance (Law 1), but the excess force ahead and downward works to move the body in the wrong directions (Law 3). All three laws are integrated, as the third column in this series (about Law 2) will show.

Applying Newton’s Laws positively gives a swimmer an advantage in efficiency over those swimmers whose mechanics apply these three laws to a negative effect.

Again, be sure to follow the laws.

Dr. Bob Colyer of Bluffton is an actively retired college professor, coach and author of “Swim Better: A Guide to Greater Efficiency for Swimmers & Instructors,” directed primarily to non-competitors.