Skydiving Science: Flying or falling?

Posted by

What goes up must come down. Pretty much sums it up, right? End of the story. But, when it comes to skydiving, not really…

Yes, of course, gravity is what makes skydiving possible. Newton figured that whole falling puzzle out a while back, but the thing is, gravity is only one of the forces at work on us when we jump (although nobody would blame you for assuming that skydiving is simply falling). Believe it or not, we as humans can fly, and no, we aren’t kidding. We absolutely can, but what we can’t do particularly well (at least on our own) is glide. But make no mistake. What we do between the time we exit the aircraft and open our parachutes is flying. 

“But wait,” you say, “I remember from high school science that everything, regardless of size or weight is supposed to fall at the same speed, so if you can’t go faster or slower, how is that flying? You’re just dropping like a stone, right?”

Well, skydiving takes advantage of a few different forces, and gravity is of course the primary one.  Although it is correct that everything from a bowling ball to a feather will fall at the same speed, that only holds true in a vacuum. Which brings us to the real secret sauce.

The real magic is the air itself, and the incredible ways in which we can put it to work for us. In a vacuum, everything can fall at the same speed because nothing is subjected to drag or air resistance. And that right there is key! In the presence of air resistance, objects with different masses will fall at different speeds due to the effect of air resistance on their surface area and shape. And this is where a term you may have heard before comes into play: Terminal velocity.

Terminal velocity in skydiving is the maximum speed a human being can reach in a specific body position. So, say you’re in freefall in that belly-to-earth position you’ve most likely seen photos of. The fastest speed you’ll reach will be around 120 miles per hour, primarily because of the surface area you are presenting to the air. The more surface area you present to the air (we call it relative wind in skydiving, which simply means the direction the wind ‘appears’ to be coming from given your perspective), the more drag you’ll be subjected to and the slower you’ll go. Which of course also means the less surface you present to the wind, as you would when falling headfirst, the faster you’ll go. 

Now here’s the really cool part. The drag that allows your entire body to go faster or slower depending on your body position also affects your limbs independently, which means that creating more drag on one arm, leg, or side of your body will push and turn you one way or the other, allowing you an incredible level of control over your movements in the sky. Your speed through the air and the drag you exert on the different control surfaces that are your arms and legs allow you to FLY!

Now of course there’s a whole lot more that goes into it, but the gist is, point your legs straight out and arms by your side and you’ll FLY forward. Arms straight out and legs on your butt and you’ll FLY backward. One arm out more than the other and you’ll turn round and round, and a thousand other tricks and combinations of body positions that all lead to the huge smiles you’ll see on countless YouTube videos of skydivers flying effortlessly through the air all around the world. 

Still trying to wrap your head around it all? Well, it’s like we always say… If you want to fly, you’ve gotta get out of the plane!

Freefall University