SWIMMERS: The Physics of Swimming



Swimmers in Darwin Pond are not anything like cartoon characters.  There was no artist who labored over a series of images, drawing frame after frame of swimmer positions, to create the illusion of motion.  Instead, there was an artist who wrote physics and motor-control algorithms, and told the swimmers to move wherever they want.  These swimmers animate themselves.  And the ways they move and turn around are determined by physics equations.  A technique called "forward dynamics" is used to create the physical effects from stroking limbs through water to move or turn a swimmer's body.  



Stroking

If you swim yourself, you probably know that using large, broad strokes with your fingers together and hands flat can help you make more effective strokes in the water.  The same principle applies to swimmers' bodies.  The larger the area a swimmer can cover in a stroke, the more that swimmer will be able to push its body along.  If a swimmer has other limbs which are not contributing to the stroke, they could cause drag, counteracting the good strokes and impeding the swimmer's momentum.  



Undulating

Swimmers also can use undulating motions (smooth, eel-like motions)  to propel their bodies.  These behaviors are usually found in the one-limbed swimmers, and sometimes in two-limbed swimmers.  Undulating is usually more energy-efficient than paddling, and can be found in advanced populations.  