Air resistance is a kind of friction or the drag force causes by the air which opposes the motion.As we have seen in free falling body, the object is falling freely to the ground because of gravitational force.Generally we ignore the air resistance but if there is too much air resistance in the motion of the body, it will decrease the velocity of the object.
F(air) = cv^2
Where, F = Resistance force by air
C = force constant
V = velocity of air
Air resistance depends on two main factors:
1. Shape of the object: If the shape of the object is very large compare to its mass, so that it has too much surface area which block too much air in the direct of the motion, the air resistance will affect the motion of object.
2. Mass of the object: If the mass of object is very less, the air resistance will come over it and it will not allow to move the object with its original speed.
Example: An object is travelling at 12 ms^-1 experience a force of 72 N. Calculate the force constant.
Velocity, v = 12 ms^-1
Force , F = 72N
Using the equation, F = cv^2
c = F/v^2 = 72/(12)^2 = 0.5
Example: A plane moving with velocity of 25 ms^-1 has a force constant of 0.5. Calculate its air resistance.
Velocity, v = 25 ms^-1
Force constant, c = 0.5
Using the equation, F = cv^2 = 0.5 x (25)^2 = 312.5 N