Air resistance

Air resistance also known as drag is a force that opposes the motion of an object through a fluid (liquid or gas). It is often associated with the movement of objects in the atmosphere, such as the flight of birds and insects, the fall of fruits and seeds from trees, and the movement of airplanes and rockets.

Overview

Air resistance is a type of friction that acts against the direction of motion. It is caused by the collision of air molecules with the surface of the moving object. The force of air resistance is directly proportional to the speed of the object, the cross-sectional area of the object facing the fluid, and the density of the fluid.

Factors affecting air resistance

Several factors affect the amount of air resistance an object experiences. These include the object's speed, its cross-sectional area, its shape, and the density of the air.

Speed

The faster an object moves, the greater the air resistance it experiences. This is because a faster-moving object collides with more air molecules per unit of time.

Cross-sectional area

The larger the cross-sectional area of the object (the area of the object facing the fluid), the greater the air resistance. This is because a larger area will collide with more air molecules.

Shape

The shape of an object also affects the amount of air resistance it experiences. Objects with a streamlined shape experience less air resistance than objects with a blunt shape.

Air density

The denser the air, the greater the air resistance. This is because denser air contains more air molecules for the object to collide with.

Effects of air resistance

Air resistance has several effects on the motion of objects. It slows down objects moving through the air, it causes objects to fall at a terminal velocity, and it generates lift for flying objects.

Slowing effect

Air resistance acts in the opposite direction to the motion of the object, slowing it down. This is why objects moving through the air eventually come to a stop unless a force is applied to keep them moving.

Terminal velocity

When an object is falling through the air, it initially accelerates due to the force of gravity. However, as it speeds up, the air resistance acting against it also increases. Eventually, the object reaches a constant speed, or terminal velocity, where the force of gravity is balanced by the air resistance.

Lift

Air resistance can also generate lift for flying objects. This is how birds, airplanes, and other flying objects are able to stay aloft.

See also

• Friction
• Fluid dynamics
• Terminal velocity
• Lift (force)