The physics behind Skydiving
Article by: Abhinav Tanksale, on 23 April 2022, at 00:12 am Los Angeles time
Skydiving is one of the oldest and most exciting sports in the world, and it continues to attract thrill seekers from all over the globe. The thrill of jumping out of a plane at up to 120 mph and free falling for several seconds is not to be understated.
A skydiver's trajectory from 30,000 feet will resemble a parabolic curve. But if you were to drop a rock off a cliff, you will notice that it falls straight down. This is because the gravitational force from the Earth on the rock is greater than the force of air resistance.
The rock will fall straight to the Earth and strike the ground at its terminal velocity. So why does a skydiver reach terminal velocity and not plummet to the ground straight away?
Falling is governed by the law of universal gravitation which states that two objects attract each other with a force that is proportional to the product of their masses and inversely proportional to the square distance between them.
This pull of gravity experienced by a skydiver is approximately 10 m/s^2. (The earth's surface gravity is 9.8 m/s^2). Since the skydiver is also falling towards the earth, and is moving at the same speed as the earth's surface, there is no friction, and thus the skydiver will fall at a steady rate.
The terminal velocity of a skydiver is approximately 130 mph (210 kph). The reason for this is that at about 75 mph (120 kph) the body experiences a force equal to its weight (acceleration due to gravity) which means that from that point on, its speed will remain constant.
The force due to wind resistance (known as drag force) depends on the skydiver's shape and the cross sectional area of the object. The drag force is proportional to the square of the skydiver's speed. Higher friction and the force of lift acting on the parachute also limit the speed.
When a diver jumps from an airplane, he accelerates rapidly toward the Earth as he drops through the sky until his speed levels out at a constant velocity. The smaller the surface area of his body that faces the wind, the faster he'll go. A skydiver will often perform various acrobatics by shifting around in any number of directions to move against and with the wind.
Typically such maneuvers will bring a skydiver down to speeds of around 120 miles per hour in the spread-eagle position but winds can take him up over 200 miles per hour if he orients his body with his head pointed down. When he pulls his parachute cord and opens up, a larger drag force slows down his fall, bringing him slowly but safely to earth.
To summarize, skydivers perform a variety of acrobatics to control their movement from place to place and make sure that they are always headed in the direction they want to go.