Speed of Terminal

[skydude2000 3]

Hi all,


I've got a bit of a melon-scratcher here. I asked my DZO this, and his answer was a little confusing. I was just wonder what people here had to say about it.

Terminal velocity is 174fp/s right? And that takes 12 seconds, 1483 feet. My logbook chart says that above, 5000m, I think, the speed of terminal increases to 200fp/s. Does it still take 12 seconds to reach terminal at that altitude? Why?


Thanks,

Skydude.

PULL!! or DIE!!

[quade 4]

Terminal velocity varies with a number of factors; drag, weight of the object in question, density of the air (aka density altitude) which takes into account pressure and temperature.

The numbers in your logbook were based on old belly to earth averages and are probably not all that accurate, but close enough for logging purposes if you don't have a freefall computer such as a ProTrack.

The amount of time it takes to get to "terminal" also varies with altitude. All other things being equal, the higher you go, the longer it will take to get to terminal velocity. The air is thinner so you can go faster more quickly, but there is also less drag.

Taken to an extreme, if you were to "skydive" from the Space Shuttle while in orbit 300 miles up with virtually no atmosphere to slow you down, you'd just continue to accelerate toward the Earth for several minutes until, of course, you did start meeting up with more and more air molecules at the very edge of the atmosphere at which point you'd be traveling so fast the friction of the atmosphere would get really pretty for us watching you. ;^)

quade -
The World's Most Boring Skydiver

[larsrulz 0]

Probably far more technical than you want, but hey....you asked for it and I'm bored at work!

For all intents and purposes, it will take the same amount of speed to reach terminal velocity as everything (density, temperature, pressure, etc) is changing enough to make any slight variations null and void for your average skydive, if you don't like numbers then stop reading now...

but if you go through the equations to calculate it out (assuming an 180 lb person whose terminal velocity is 120 mph at 5000 ft with a static temperature of 0 deg C from surface to max altitude--mind you weight/terminal/altitude/temperature chosen will not influence the final outcome only the numbers used in this particular calculation) you get the attached spreadsheet.

Just ignore the miscellaneous information, unless you want to see that I'm not just pulling this out of my ass, but if you compare 5K, 10K, 15K, and 20K exit altitudes, you get 11 sec, 11 sec, 12 sec, 14 sec (rounded to the nearest half second) respectively to be within 2% of terminal velocity.

Like quade said above, the higher you go the more serious it gets, but even a 30K exit only increases time to terminal to 17 seconds from 11. The main reason for this is because (while it appears to be near sea level) air density vs. altitude is not linear, so the further away from sea level you go the more influence another 5K feet will have.

I got a strong urge to fly, but I got no where to fly to. -PF

[kallend 2,131]

Skydiving is a physics-driven sport.

Maybe 15 minutes of basic Newtonian physics should be part of all FJCs.

...

The only sure way to survive a canopy collision is not to have one.

[popsjumper 2]

Forget Newtonian....
Einstein's theory of time and space, special relativity, proposed that distance and time are not absolute.

Try that on at FJC.

My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

[fmmobley 0]

Quote

Forget Newtonian....
Einstein's theory of time and space, special relativity, proposed that distance and time are not absolute.

Try that on at FJC.

Andy, maybe if we fall fast enough we will go back in time and we will be young again !

... Marion

[tbrown 26]

Quote

Quote

Forget Newtonian....
Einstein's theory of time and space, special relativity, proposed that distance and time are not absolute.

Try that on at FJC.

Andy, maybe if we fall fast enough we will go back in time and we will be young again !

I fall fast enough to feel young again, but it hasn't brought back the days of an $8 ride to 12.5. Distance and time may not be absolute, but ground rush and impact certainly are, so I go along with the Newtonian notion of getting something over my head by 2 grand. USPA must be run by a bunch of Newtonians, though only Einstein can explain some of the weird delivery dates of my Parachutist Magazine (nyuk-nyuk).

Your humble servant.....Professor Gravity !

[ntrprnr 0]

"Once this baby hits 88 miles per hour, you're gonna see some serious shit."

...Is what I think you were trying to say. :)

_______________
"Why'd you track away at 7,000 feet?"
"Even in freefall, I have commitment issues."