# Air Resistance

Air resistance is the force acting on an object that is moving through air flowing in the opposite direction. The air “resists” the object’s movement, slowing it down by friction that is created as the object collides with air molecules. Air-resistance force is a component of fluid dynamics, with an important role in design applications in such fields as aerodynamics, hydrodynamics, and astrophysics.

Also known as “aerodynamic drag” or simply “drag,” air resistance is proportional to velocity: the faster an object’s movement, the greater the air-resistance force. All objects moving through air are impacted by air resistance, but it has a significant effect on objects moving at high speeds, such as airplanes and trains.

The amount of air resistance can be calculated with air-resistance formulas (also called air-resistance equations), which include the variables of velocity, area, air density, and drag coefficient. The object’s velocity and its cross-sectional area, in particular, are the two factors that most directly affect the level of air resistance - increased velocity or increased cross-sectional area of the object will increase the amount of air resistance. Calculations of the amount and specific type of air resistance are essential when designing many types of objects, especially those where power and efficiency are important.

### Synonym

Aerodynamic Drag

### Related terms

Air Resistance Definition / Air Resistance Formula / Air Resistance Equation / Air Resistance Force