Mechanics

# Air Resistance Force

Skydiver gliding due to air resistance force

If a body moves through a fluid (a gas, a liquid or a vapour) there is a force that opposes this movement. When it comes to air, this force is called the air resistance force. It is thanks to this resistance that the parachute exists.

When a body is in motion, it suffers the action of dissipative forces, among which we can mention friction and air resistance.
For the motion of a body in contact with the air (such as free fall, the motion of a motorcycle or an airplane) with any speed, the force of air resistance is given by:

Don’t stop now… There’s more after the publicity 😉

r = K . v 2

Where k is a constant that depends on the shape of the body and the cross-sectional area of ​​the body, perpendicular to the direction of motion.

In formula 1 cars, for example, aerodynamic shapes decrease the value of K, which helps to decrease air resistance in these vehicles, causing them to gain more speed.
In parachutes, for example, their aerodynamics increase the value of K, consequently the air resistance increases.

We can say that the air in the parachute works like a strong wind, pushing it up, easing the fall.