At this point, I feel like the only thing I have left to do is to fully relate my topic to the activity of skydiving. I’ve talked about it a little bit in terms of terminal velocity, but I haven’t fully explained all the real life applications of the various part of the drag equation for skydivers.
If we go back to that equation, we’ll see that there are four variables: the object’s velocity, coefficient of drag, and reference area, and the fluid’s density. When increased, all four of these things increase the drag force as well. Similarly, a decrease in any of those will decrease the drag force.
This is extremely important for a skydiver, whose terminal velocity is entirely dependent on the drag force exerted on him. The greater the drag force, the lower the terminal velocity. The smaller the drag force, the faster the diver can go before topping out.
Because all four of those variables are part of the larger drag force, this means that skydivers can affect the drag force in many ways, many of them equal. If two equally dressed skydivers found a way to double the reference area for one person and to double the drag coefficient for the other, they would experience equal drag force at equal conditions.
Skydivers can affect these variables in many ways. Their velocity and the density of their surrounding air are largely out of their hands, but they can change their coefficient of drag by changing the material they wear. A baggy t-shirt would have a higher drag coefficient than a scientifically designed skydiving suit (hence why they exist..). Similarly, skydivers can change their body position to change their reference area. When divers are chest-down with their limbs extended, they will experience a much greater drag force than when the are faced head-down with arms at their sides because of this change in reference area. If you’re skydiving, this means that you will experience less drag force and be able to reach a higher terminal velocity in a head down position than with a ‘flat’ or sprawled out position.
This is also why the parachute works to slow down the diver once they have reach the point at which they need to deploy it. When the parachute is deployed, the reference area (and possible the drag coefficient as well) skyrocket. This results in a large increase in the drag force, so that the drag force is actually greater than the skydiver’s weight. This results in deceleration as long as there is an imbalance of forces. This deceleration (obviously) causes the diver to slow down, until he or she has reached a new terminal velocity where the drag force once again equals the skydiver’s weight. At this point, the skydiver simply drifts down towards the earth with a much more reasonable/slow velocity, acceptable and safe for landing!
Seeing as how this is my last blog post, I thought I would revisit my learning objects and give a progress indicator and short explanation for each:
1. Understand the relationships between air resistance, terminal velocity, skydiving, kinematics, and Newton’s laws.
100%. I have a really good understanding of how these things fit together.
2. Learn to calculate air resistance based on the formula D = (1/2)*p*u^2*Cd*A where D is the drag force (like air friction), p is the density of the fluid, u is the object’s velocity, Cd is the object’s drag coefficient, and A is the object’s cross-sectional area.
100%. It’s pretty much just plugging numbers into the equation; simple.
3. Solve physics problems involving air resistance as it pertains to kinematics and to Newton’s laws.
100%. I solved a problem in my last blog post, and it went well.
4. Understand how the positioning of skydivers affects their velocity, drag force, etc.
100%. Position doesn’t directly affect velocity, though – it affects drag, which then affects velocity.
5. Reach a solid conceptual understanding of the physics behind skydiving, and of why skydivers feel so safe jumping out of planes.
90%. I understand now that parachutes increase reference area so much that a skydiver is just as physically inclined to slow down as he was to speed up due to gravity. Physics don’t fail. I still don’t know if I trust the cords on the parachute, though…
Physics of Skydiving 
I really enjoyed reading your blog about the physics behind skydiving. I found your posts to be informative and you provided a good explanation for why people jump out of planes. I am still a little bit confused about cross-sectional area (and the drag coefficient). Perhaps, if you were to continue writing this blog, it would be good to go into how to calculate the area when given the size and shape of an object. I understand that there are multiple ways of doing this, but an example calculation would be helpful. Does it depend on the center of mass? The orientation of the object?
Also, I would like to know how skydivers are able to change positions mid-flight.
Hey andy
very informative post and this topic is very interesting
I understand everything you are saying except I dont really understand your explanation of cross sectional area
maybe you could give us an example of this topic or a sample calculation
I have read through a majority of your posts and I completely agree with you that you that you have practically mastered all of your objectives. I love your blog and I think you did a great job with your topic. Just to give you one suggestion maybe for a future post (even thought this is the last one) you could research a little more on what goes into the scientifically designed skydiving suit that you mentioned sky divers wear and why the components of the suit increase their terminal velocity.