Air resistance, also known as drag, is a type of fluid friction that acts on objects moving through air. When an object moves through air, it collides with air molecules, creating a force that opposes its motion. This resistance force depends on several factors including the object's speed, shape, and cross-sectional area.
The drag force equation shows that air resistance depends on several key factors. The force is proportional to the square of velocity, meaning doubling speed quadruples the resistance. It also depends on air density, the object's cross-sectional area, and the drag coefficient which relates to the object's shape and surface properties.
When an object falls through air, it initially accelerates due to gravity. As its speed increases, air resistance grows stronger. Eventually, the upward drag force equals the downward gravitational force, creating equilibrium. At this point, the object reaches terminal velocity and continues falling at constant speed.
The shape of an object dramatically affects air resistance. Streamlined shapes, like teardrops or aircraft wings, allow air to flow smoothly around them, minimizing turbulence and reducing drag. In contrast, blunt shapes create separation and turbulent wake regions behind them, significantly increasing air resistance and energy loss.
Air resistance has numerous practical applications. Parachutes use large surface areas to maximize drag and slow descent. Vehicle designers optimize aerodynamics to reduce fuel consumption by minimizing air resistance. Sports equipment like golf balls use dimples to control airflow, while aircraft wings are carefully shaped to balance lift and drag for efficient flight.