Forces Acting on a Parachute

Aerodynamics
Parachutes work on the principles of gravity and air resistance and in effect, terminal velocity.
Air resistance (air friction)
Air resistance is an upward force exerted on a body while it is in the air and is the result of air molecules that come in contact with the surface of the falling object. This force attempts to counteract gravity and other downwards forces influencing a body. The amount of air resistance encountered by an object is dependent on two factors: speed of the object and surface area. Air resistance acting on a body is directly proportional to the speed of the falling body and this key principle demonstrates that an increase in speed causes an increase in air resistance. Similarly, the air resistance is also dependant on increases in the surface area of the falling body. Practically, a small, streamlined object will experience less air resistance than an object with a large surface area since more air molecules come in contact with the object’s surface. Likewise, a parachute decelerates the falling body by increasing the surface area, which causes the force of air resistance to overwhelm the force of gravity, thus the net force and acceleration is upward. In effect, the falling object slows down.
Terminal velocity (constant speed of an object in a certain direction)
Terminal velocity is the constant, maximum velocity of a falling object in air. The air resistance on a falling body will increase with its speed until the upward force of air friction is equal to the downward force of gravity on the body. At this point, there is no net downward force on the object, and from Newton’s first law of motion, the acceleration then becomes zero and the object falls at a constant terminal velocity. Ideally, a parachute will slow the object’s speed by creating air drag that eventually overpowers the force of gravity, causing the falling object to decelerate. However, since the air drag is dependent on the velocity, the air resistance