Overview

In sport and exercise science, understanding how external forces affect the body or equipment is crucial to enhancing performance. Three important forces that affect motion in fluid environments (air or water) are buoyancy, lift, and drag. These forces influence how we move, how fast we travel, and how efficiently we perform in sports that involve air or water resistance, such as swimming, cycling, rowing, skiing, and projectile sports like archery or shooting.

Buoyancy is the upward force that a fluid (usually water) exerts on an object submerged in it. This force counteracts the object's weight, making it appear lighter in water. Buoyancy is why swimmers float and why objects like life jackets keep people above the surface. Whether an object floats or sinks depends on its density relative to water. If the object is less dense than the fluid, it will float to the surface. In sport, understanding buoyancy is vital in aquatic disciplines—swimmers and water polo players benefit from streamlined, horizontal positions that minimise drag and maximise the effect of buoyancy to stay near the surface with minimal effort.

Lift is the force that acts perpendicular to the direction of motion and is caused by differences in pressure on opposite sides of an object moving through a fluid. Lift is most commonly associated with objects that spin or have specific shapes, such as wings, curved surfaces, or spinning balls. This force is explained by Bernoulli’s principle, which states that faster-moving fluid creates lower pressure.

In sport, lift is used to alter trajectories and improve performance. For example:

A spinning football can bend in flight (as in a free kick) due to the Magnus effect, a type of lift force caused by the ball’s rotation.

In ski jumping, the athlete’s body acts like an airfoil, utilising lift to stay airborne for more extended periods.

In swimming, skilled athletes use body position and arm technique to generate lift and maintain a higher, more efficient glide.

Drag is the resistance force that acts opposite to the direction of motion as a body moves through air or water. It is a major factor that slows down movement and reduces efficiency. Drag increases with speed, surface area, and fluid density. There are different types of drag:

Form drag, caused by the shape of the body or object

Surface (or friction) drag, caused by contact between the fluid and the surface

Wave drag, specific to water, is caused by the creation of waves

Athletes reduce drag by improving streamlining, wearing tight-fitting clothing, and using aerodynamically designed equipment. Cyclists, swimmers, and skiers all benefit from reducing drag to move faster with less effort.

Together, buoyancy, lift, and drag explain much of how motion is controlled and influenced in fluid environments. Mastering these forces helps athletes enhance speed, accuracy, and efficiency—whether it's flying through the air, gliding through water, or striking a perfectly spinning ball.