How can a swimmer move forward without touching the bottom?

A swimmer crosses a pool with no wheels and no ground to push against. Water itself provides the push. Hands, arms, feet, and legs move water, and the water pushes back on the swimmer.

During the useful part of a stroke, the swimmer gives some water backward motion. The water exerts a forward force on the body. These opposite forces do not cancel because one acts on water and the other on the swimmer. Pushing against water is harder to see than pushing off the solid pool wall, but both involve an interaction.

A hand does not simply travel in one straight line, and different swimming strokes use different movements. Angles and timing affect how much of the water’s force helps move the swimmer forward. Kicking can contribute to propulsion and help keep the body aligned.

Water also resists the body moving through it. A body position that disturbs less water can reduce this drag. The swimmer advances when useful pushes overcome resistance; between pushes, drag can slow the glide. Beneath the splashes is a repeating conversation of forces between a person and the pool.