What is the Physics theory behind Sky Diving?

Before we go into the science, you may be wondering what’s the difference between skydiving or parachuting. The main difference between skydiving and parachuting is that in skydiving, the skydiver freefall before deploying his parachutes, and in parachuting, the parachutist deploy his parachute straight away.

Skydiving begins with that leap out of the airplane and skydivers fall for between 30 and 90 seconds, flying their bodies to perform tricks or create formations on the way down.

What is the science of skydiving?

When the skydiver leap off the plane, two forces act on his body:

1. The earth’s gravity pull that is pulling the skydiver downwards
2. The air resistance pushing the sky diver upwards.

The air resistance depends on two factors:

1. The speed of the falling object
2. The surface area of the falling object

When the skydiver leaps off the air plane, he free fall as the earth’s gravity pulls him towards the earth. He falls with an acceleration of 9.8 m/s². However, as his falling velocity increases, the upward frictional force, air resistance also increases to oppose the downward falling motion. Hence, his velocity increases, but at a decreasing rate because of the opposing air resistance.

How the skydiver position his body makes a lot of difference. If he wants to fall faster, he simply need to reduce his surface area by falling head or feet first.

Photo by form PxHere

To slow down,  he spread his position in a spread-eagle position. In this position, the upward air resistance is greater because of a larger surface area.

Photo by form PxHere

The upward opposing air resistance will increase until it eventually equals the weight of the falling skydiver. At this point, the skydiver has reached its terminal velocity and its velocity remains constant, i.e., there is zero acceleration.

Note that at terminal velocity, where there is no acceleration, where air resistance equals his weight, he is still falling downwards with a constant velocity (terminal velocity). This is in accordance to Newton’s first law that an object continues its motion.

What happens after he opens his parachute?

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When the Skydiver opens his parachute, air resistance increases further because of the increase in surface area. The falling speed of the skydiver decreases causing the air resistance to decrease. A final lower terminal velocity is then achieved when the total upward air resistance equals the downward weight. Hence the following graph shows a lower terminal velocity being achieved.