Air resistance is a frictional force which occurs when air passes over the surface of a body. This frictional force is not just limited to air though and it applies in fluids, usually water in a sporting situation. Air resistance, drag, and fluid resistance mean the same thing.
Four things affect the amount of air resistance; the velocity of the body or air, the cross-sectional area, the shape of the body and type of surface.
- Velocity - the faster the body is travelling through a fluid (or air), the greater the air resistance. Can you think of three sports where this is relevant?
- Cross-sectional area - the greater the cross-sectional area the greater the air resistance. Can you think of three sports where athletes try to reduce their cross-sectional area as much as possible?
- Shape - pointy shaped objects cut through air resistance more easily, for example, an F1 car or the shape of a track cyclists helmet.
- Surface - a rough surface will create more air resistance or drag than a smooth surface. Remember the Speedo LZR full-body swimsuit which significantly enhanced a swimmers performance by holding the body in a more aerodynamic position and repelling water from the surface? The dimples on a golf ball actually decrease air resistance making a golf ball fly further through the air than a smooth ball (https://www.youtube.com/watch?v=fcjaxC-e8oY).
An aerofoil is a streamlined shape which minimises cross-sectional area and drag of air passing around it.