The force of friction applied by the air against a moving/flying object is known as air resistance. It is the opposition provided by the air that resists the motion of an object or tends to slow down the speed with which it is moving. Air resistance force is also known as drag. The magnitude and the intensity of the air resistance force are directly proportional to the speed of the moving object. This means that the greater be the speed of the moving object, the bigger will be the air resistance force experienced by it. Air resistance force is an inbuilt force in nature. It is proportional to the surface area of the object. The more be the surface area of the object, the greater will be the air resistance force experienced by it.
1. Riding a Bicycle
When a bicycle rider moves in the forward direction, a force of friction exerted by the air tends to slow down its speed. This force of friction is exerted on the rider’s face and body from the direction opposite to the direction of motion of the bicycle. When the rider increases his speed, the air resistance force increases proportionally. Crouching down on the bicycle helps the rider to reduce the effect of air resistance force and move with an improved speed.
Air resistance force plays a very important role in the action of a parachute. When a person jumps down while sky diving and opens up his/her parachute, the air resists the jump. Due to this resistance provided by the air, the speed with which the parachute approaches the ground slows down. The gravitational force pulls the parachute in a downward direction, whereas an air resistance force is applied to the parachute in an upward direction. Hence, the air resistance force helps the person to land smoothly on the ground.
3. Walking in Storm
It is often difficult to walk in stormy weather. While walking against the direction of the wind, a considerable amount of resistance is felt by the person that causes difficulty in walking. The same reason makes it difficult to hold an umbrella in hand in the presence of a strong wind.
4. Feather Falling on the Ground
A feather when falls on the ground from a certain height, it tends to float and move slowly towards the ground. The force attracting the feather towards the ground is the gravitational force, while the force that resists the fall and motion of the feather is the air resistance force.
5. Paper Plane
A paper plane floats smoothly in the air if constructed properly and to achieve this, the front side of the paper plane is made sharp. This sharp edge helps the paper plane to cut through the air and avoid the air resistance force. This helps the plane to advance smoothly and swiftly.
6. Light Objects Floating
The objects that are lighter than air, or the objects having a low mass, do not fall on the ground directly, instead they tend to float in the air. The force applied by the air on the object in the upward direction is known as the air resistance force. In case the object is thrown from a height in a vacuum, it tends to fall on the ground directly because there will be no air to provide the air resistance force and oppose the motion of the object.
The engine, wings, and propellers of an aeroplane are designed in such a way that enough thrust can be generated that helps the plane to overcome the air resistance force. The friction introduced by the air is also responsible to generate turbulence. However, air resistance causes no difficulty in the case of a rocket because a rocket has to exhibit motion in space, which is an environment that does not contain air, and therefore, it is free from air resistance force.
8. Tree Shedding Leaves
When a tree sheds its leaves, they float in the air for a while and finally land on the ground. This is because a significant amount of air resistance force is applied to the leaves by the air in the upward direction. This force helps the leaves to stay in the air for a while before falling on the ground. A force opposite to the air resistance force acts on the leaves in the downward direction that attracts them towards the centre of the earth. In the absence of the gravitational force, the leaves tend to float in the air till eternity. Similarly, in absence of the air resistance force, the leaves do not float and fall directly on the ground.