As an object falls, it has to push past all the atoms and molecules in the air. If there were no resistance, everything would fall at the same speed, dictated by gravity. A rock is heavy and small so it pushes atoms out of the way easily. A feather, on the other hand, weighs much and has a relatively large surface, so it runs into a lot of atoms and has trouble pushing them away. The wide area of a parachute's lightweight and flexible fabric creates a large amount of air resistance. Air molecules underneath the parachute move up and create an opposing force to the gravity that propels you toward Earth. The nylon or silk fabric of a parachute is strong enough not to tear and elastic enough to create the maximum drag.
The terminal velocity of a skydiver is about 125 mph, which takes about 15 seconds to achieve. Gravity provides a downward force of 32.18 feet per second as you fall. Air drag is proportional to the square of an object's speed and also depends on the area of the object. The drag of a parachute increases while falling until it's equal to the weight of the parachute plus human, at which point acceleration decreases to zero.
A rip cord helps a parachute deploy properly and reduces the stresses involved. A handle attaches to a steel cable that ends in a closing pin that prevents a spring-loaded pilot chute from opening. When you pull the rip cord, the pin moves and opens the container, releasing the pilot chute and opening the parachute.
Round parachutes are useful in some emergency and military applications. They provide drag but no lift and are inherently unstable from oscillations. Newer square or cruciform parachutes have decreased oscillation and can turn more smoothly. A parachute with a tapered design improves speed adjustment and control because of its variable resistance along the surface. A rectangular design causes a dense fabrication of air cells under the parachute, which leads to a safer landing. Modern parachutes tend to use a parafoil design, which has controls like a paraglider. Their top and bottom layers of fabric connect together into cells, creating high pressure air inside that causes aerodynamic lift.