The Skeptics' Guide to the Universe > Podcast Episodes

Episode #349

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Steven Novella:
This Day in Skepticism: Exxon Valdez
News Items: Superhero Pseudoscience, High Altitude Skydiving, Nuclear Clock, New Hampshire Abortion Bill, NDE and Lucid Dreaming, Designer Electrons
Who's That Noisy
Your Questions and E-mails: Here Comes the Metric System
Name That Logical Fallacy
Science or Fiction    This week's topic is:
Availability Heuristic
Connect with the

seaotter:
Thanks for the podcast!

wallet55:
So, though I would not hold out my skydiving past as a reason to completely trust my opinion on these high altitude jumps, mainly because what this guy is doing is so radically different from what we sport jumpers do jumping say from 15 thousand feet (my highest jump).
There are really 3 dangers here as i see them and two of them are completely outside of the realm of sport jumping.
1) it is extremely cold
2) there is no air to breath
3) there is no airspeed for a very long time with which to maintain stability in freefall.

The first two items mean that everything about this jump is really about your spacesuit's integrity. Kittinger's glove had problems which nearly cost him his hand. A Russian who did a high altitude hop and pop (opening the chute at the beginning of his jump), died when his suit failed.

the third is similar to what people experience when jumping from any balloon or hovering helicopter, albeit to a much greater degree and longer time. The jumper at high altitude is basically going to rotate and spin for a while until enough air rushes by by which he can stabilized himself either through positioning or a drogue chute.

Lacking any memory of Kittinger describing the deceleration as difficult, I am thinking that Dr. Novella's worry over this is excessive. I know I decelerated from  an ultra dive of (what i was told) was close to 300 mph to the normal 120 in just seconds, and it was exhilarating, but not really painful or particularly risky.

The spin and blackout is something that has killed sport jumpers (particularly tandem jumpers before they started using drogues to prevent the passenger from getting them in a spin), and entanglements with their own and others chutes still kill jumpers today.

So when you get down to it, this jump is mainly dangerous because of where they are doing it (at the edge of space) not what they are doing.

Anders:
Rebecca, Freud actually thought most things were a sign of masturbation.

Evan, an inch is 2.5 cm. I am so disappointed.

Belgarath:
I would agree with the comments of Wallet55.

Aerodynamically, the only issue is getting up to a speed at which the jumper could control a spin.

The thought of how the jumper would be essentially exceeding terminal velocity as they got into the lower, denser atmosphere seems to be flawed because you would need to apply a greater force (essentially a thrust) to do so.  YES, the gravitational force would increase as you descend, but my guess would be that the density of the atmosphere increases at a greater rate, slowing you back down to terminal velocity.

The important thing about terminal velocity is that for any given body configuration, you shouldn't be able to exceed that speed within a given atmospheric density because you would need to apply thrust to do so.  (I suppose you could momentarily exceed it by falling headfirst, then adjusting your body orientation quickly to falling face down. You would quickly slow back to terminal velocity for that body orientation)

Think of it this way, what if the atmosphere got thinner as you descended?  You would accelerate to the new terminal velocity as you moved into the thinner and thinner air.

I suppose I could go dig out my old aerodynamics books and find the equations that govern this,  I used to give a problem regarding this to my students to demonstrate the variations in atmospheric density as you descend.  This was in airplanes but essentially the same principle applies to a skydiver.

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