There are four principles to consider:

1. Weight of the swimmer
2. Buoyancy - ability to float
3. Thrust - arm stroke and kick
4. Drag - pressure and skin friction

Almost everyone has "tread water". This usually means moving both arms out away from the body, again and again. The arms stay near the surface. The legs and feet move in somewhat the same way. This creates lift, which keeps the swimmer's head above water.

A swimmer can use these same principles to swim, by moving his arms like a paddle wheel or propeller. This creates lift and forward thrust. At this point drag becomes a problem. Drag comes in two forms: the frontal area of the swimmer is going through the water, which creates a separation of flow behind the swimmer. This creates the most drag. The second form of drag is skin friction. This is minor.

Overall drag is reduced if the swimmer is "streamlined". This means creating enough lift to bring the whole body near the surface of the water and keeping the body straight.

Swimmer Producing A Lot Of Drag	Streamlined Swimmer

Arm Stroke

For a while it was thought that short, swift arm strokes would be the best. To test this idea an inventor built a caterpillar paddle wheel (short paddles that turned swiftly). The boat almost stood still! It was found that long, straight paddles that turned like a propeller were best.

Paddle Wheel Arm Pull	Caterpillar Arm Pull

As mentioned before, the fastest swimmers also generate (create) thrust by moving their arms and hands like a propeller to generate a lift type force. The hands stay flat and each arm takes a turn. The lift, created by the arms turning, brings up the front of the swimmer's body. It also gives thrust or forward motion to the swimmer.

Kick

What about the back part of the swimmer's body? The legs and feet "kick" to provide (give) propulsion (forward motion) and stability (return to the streamlined position the swimmer originally had). The legs or feet must not come out of the water. If the legs and feet come out of the water, air comes into the water with the legs and feet and adds drag.

Different kinds of kicks are used. One kind for short, fast races and another kind for long distance swimmers. If the strokes are steady, the kicks together with the strokes and the body kept streamlined (straight), the swimmer will be able to go very fast.

Famous swimmers like Mark Spitz use these same principles when they swim.

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Last modified: Fri May 29 08:56:56 PDT 1998