CWT - What happened to gravity during freefall?

[ptoot]

During my last few CWT dives I did some freefalling and this got me thinking:

I looked at various freedive graphs (eg Manual of Freediving p.160-161) and they show hardly any acceleration from the moment the CWT diver theoretically stops finning and continues in freefall.

I realise that drag is a major player here, but does that complete take out the element of gravity? As volume (buoyancy) reduces I expect some acceleration kicking in...

Does a no limits dive (wedge shaped finkeeper and lots of weight on) accelerate?

What is the terminal velocity for a human diver (neutrally weighted at 10m / half depth)? Is it just over 1m/s ?

 

[Mullins]

You reach terminal velocity quite quickly, i.e. speed at which weight is balanced by friction. Buoyancy change from 30m onwards is very slight, so you'll only speed up by a very small amount from, say, 40m onwards.

Terminal velocity depends on a few factors so it's very hard to give a definitive answer to that one. If I weight myself to be neutral at 20m, I sink at 1.5m/s (streamlining) from 70m onwards.

 

[ptoot]

@mullins:

thanks for your quick reply! what about a nolimits or vwt dive? Does the weighted sled accelerate?

 

[Mullins]

Not sure about that, but I expect they'd hit terminal velocity pretty quickly as well. I suppose the only thing preventing an object hitting TV immediately is its inertia, and while a sled has more inertia than a diver it's still not a huge object. Check out the graphs of Herbert's nutcase 200m+ dives, they should be on the net somewhere.

 

[Bill]

Just to back up what Mullins says, come to a stop at 12 meters (assuming neutral at 10) and then try free fall. The D3 readout will prove it.

 

[Drejcha]

Does a no limits dive (wedge shaped finkeeper and lots of weight on) accelerate?

for the infinite dive it would - very little, from some point on it's practicaly negligible.

terminal velocity is just the matter of resultant of gravity force, buoyant force (which is obviously variable), and resistance of water (larger speed -> larger resistance). without the resistance, you would never reach the terminal velocity. if you want to go faster - suit, position of the body (and eventual the fin) is just what you can work on.

pretty much like skydiving. skydivers reach terminal velocity as well; though buyoancy factor is negligible there, terminal velocity depends mostly on position of the body - the same as in the water.
more about it:
Speed of a Skydiver (Terminal Velocity)
and:
[ame="http://en.wikipedia.org/wiki/Terminal_velocity"]Terminal velocity - Wikipedia, the free encyclopedia[/ame]
(check: terminal velocity in the presence of buyoancy force)