We can agree on this, its 90 seconds if you include the body position and the fact that the parachute was opened slowing them down AND it was 2 people midway through.....

The only thing that will affect the difference in time for two bodies to fall to earth is the difference in friction. All bodies -- regardless of weight -- accelerate at 32 ft/sec/sec. Friction (wind resistance) will be the only variable factor. You can thank Mr. Newton for that theory.

Ok you guys made one small mistake. But most likely it was due you safty precautions. But when Grant tried to have a conversation during free fall was not done as in the movie. In the movie they both faced one another which would allow a conversation to be heard. When Grant tried he was over 2 feet away from the person talking. There was no way he could hear a conversation like that. They need to do it facing one another to try and prove that part of the myth.

In the last myth the plane must have circled back around. It is possible to close the horizontal distance as they did (that was a very dangerous pass) but even with a strong headwind giving only 60mph ground wind they would also have had a horizontal seperation of a quarter mile. No way they could make up horizontal seperation and straight line vertical seperation of 15sec. Groups of jumpers are usually given 5sec. seperation between them to ensure groups don't drift on top of each other.

quote:

Originally posted by weretigerf:
Ok technically didn't the third test for the free fall. (the catch up) discredit the
first.?

Since the dummy did not attempt to slow down his fall the way Swayze did? By stretching out its (aka posing the dummy's) body

You are completely correct... and that simple fact invalidates their first conclusion.

quote:

Also why did they have a second skydiver in the second part (mid air conversation) wouldn't they just need to have him talk to the guy he was strapped too. Since technically, that was the same position the 2 were in in point break?

Correct, again... and that fact invalidates their second conclusion.

quote:

I would say they would have to revisit this myth again?

Absolutely!

quote:

Originally posted by natelloyd:
Tory with a high-drag pose and Kari with a low-drag pose, they gave terminal velocities for both. Tory's terminal velocity was stated to be ~120 MPH. Kari's was ~250 MPH.

Sorry Nate, but that is not correct. Kari NEVER reached 250 MPH in the episode! In fact, IIRC she never skydived at all. What they DID show was the practice windtunnel at 120 MPH, with Tory floating and Kari still standing on the ground. SO we only know that Kari would have fallen faster than 120, but we have no idea how MUCH faster. The over 200 number was ONLY for the stunt skydiver.

As has been correctly described above, the time to impact for a person (or person like object ) from 4000 is not given solely by 32 ft/sec/sec, you must also figure in drag and terminal velocity. For a terminal velocity of 170 ft/sec, the 31 seconds is close to correct. The time from 8000 will NEVER be exactly twice 4000 feet, because some of that time is spent accelerating to terminal velocity.

I have never seen the movie, but I suspect that 90 seconds fall time was a combination of non-overlappable cuts and segments. If Keanu does nto follow them for 15 seconds, then you can add 15 seconds of fall time to ANY sequence that shows both in the air at once. Take the longest screen cut of Keanu falling solo and add that. Then ALL the cuts that have them fighting, talking, or anything else can be added together. This will easily exceed the longest physically possible fall time from the advertised starting altitude, because the director wants to distort physics to increase drama. But it also means that the sequence as show is nto physically possible. Which the MythBusters confirmed.

And yes, the stunt dummy standing in for the Buster, flailing away as it fell, would fall a bit faster than trained sky diver, but not by a huge amount, and certainly not enough to stretch 31 seconds into 90! And when Swayze and Reezes were holding onto each other and falling, the doubled mass with only slight increase in wind resistance would have caused them to fall FASTER, not slower.

While the question of lowest possible safe parachute deployment altitude, and ability of a single standard chute to safely slow two adult males is an interesting addition to the myth as well, it suffers from several problems that make it hard to test. Minimum safe deployment altitude changes drastically between parachute designs (Ballistics chutes for recovering ultralight airplanes safely deploy under 100 feet AGL, and have save4d lives even when deployed 60 AGL!), but also to a lesser extent on packing variations, local wind and eddy currents, the exact angle and position of the body the moment the cord is pulled, and many other minute variables. Worse, what constitutes 'safe' landing? They have had trouble with this criteria many times before. And since people are known to have survived falling from 30,000 feet with NO parachute, it obviously also includes many random factors. Al told, it becomes nearly impossible to pick the exact correct parachute, packing qualities, opening conditions, and impact conditions combined with chances for injury. But it _could_ make for some fun testing ! As long as no PEOPLE are involved in the splat tests!

Mike

quote:

Originally posted by juniorbuster:
in the myth on the new episode about a 90 second free fall that eventually go busted could be plausible!!! If you are flying in a high altitude area at 4000 feet above the ground, your aircraft is set to the ground level. But if you are landing at an area at sea level you need the ATC to tell you what the ground level is at. You need to be flying at IFR or instrument flight rules or be about to land to be told that. So, if you are coming from a place that is 5000 ft above sea level and come into a place that is 1000 ft, you would be at 8000 feet!! Which could take more that 90 seconds to hit the ground!

Altimiters measure pressure altitude. If the strip you are landing at is 4000', when you land your altimiter reads 4000', not zero. If you fly from a 5000' airport to a sea-level airport without adjusting the pressure, your altimiter won't be accurate, but it will be something close to zero.

The real question is what is the altitude of the ground at the test site and the movie site. If the test site was 3000', then the dummy only fell 1000'.

quote:

Originally posted by skeptic:
There two myths from the Point Break scene they did not test:

1. if the second skydiver could catch the first would it be possible to hang on when the parachute opened?

2. Would a standard parachute of the type used support that much weight?

Personally I think these would be more "scientific" to test then using myths based on timing calculated from an action sequence screen time

quote:

I have never seen the movie, but I suspect that 90 seconds fall time was a combination of non-overlappable cuts and segments. If Keanu does nto follow them for 15 seconds, then you can add 15 seconds of fall time to ANY sequence that shows both in the air at once. Take the longest screen cut of Keanu falling solo and add that. Then ALL the cuts that have them fighting, talking, or anything else can be added together.

It's simply not possible to determine "movie time" from a scene like this.

You can look up the scene on youtube if you want, but you just cannot determine whether any two cuts without dialog were intended to be concurrent or sequential.

For example, in the scene, Swayze jumps, and you see one continuous shot of him falling. This lasts approximately 6 seconds. It then cuts to Keanu freaking out, and then approximately 9 seconds later, he jumps.

So in real time, it has been 15 seconds from the time that Swayze jumps to the time that Keanu jumps. This is the timing they use in the "myth." The thing is, those two scenes could EASILY be happening at the same time. If they were, then in "movie time" he jumped a mere 3 seconds after Swayze, not 15! It doesn't necessarily have to be exactly overlapped either, so he could have jumped 3,4,5 or whatever seconds later. (Frankly, the wide angle shot a few moments later showing how far away keanu is from swayze supports a "movie time" of less than 15 seconds). Kind of a big difference between 15 seconds and 3.

The same can be applied to a lot of the scene. It's not possible to determine the "movie time" of the fall.

You know, I do not think changing your body position on a 4000 foot fall is not going to add more than a few seconds. Certainly is not going to turn 31 seconds into 90 seconds. Also you have to open your parachute in enough time for it to open and you to de-accelerate. Maybe about 10 seconds before you hit the ground. So you really would have about 20 seconds of falling time before deploying the parachute anyway. Maybe if you opened your parachute right away, it probably be closer to 90 seconds, but that is not how it happened in the movie.

It seems more like a scripting error and film editing blunder than anything. Just remember it is "Hollywood" bending the laws of physics to fit the story of the movie. This remains "Busted" to me.

quote:

Originally posted by wildmousex:
what i want to know is "where's buster"? that free fall should have been done by buster, not some pansy simulaid with what i can only describe as firecrackers for guts.

Speaking of those "Firecrackers" (I call 'em shotgun shells), does anyone find those things rather strangely disturbing?

Long time Mythbuster fan; first time poster.

Was reading an old ESPN The Mag earlier today and there is an blurb about Travis Pastrana skydiving from 12,500 in shorts and socks and no parachute!

http://expn.go.com/expn/story?id=3055619
and

http://expn.go.com/expn/slideshow?id=3055877§ion=expn.2007.motox&count=0

The second is a slide show of the jump; the difference between this and Point Break (and Mythbusters) is that another skydiver (with a chute) grabs and hooks himself to Travis, then opens the chute.

CRAZY!

as far as the freefall time of 90 secs......thats totally not possible from 4000ft or 8000ft. the dummy was very accurate with its fall rate. I promise you it didnt fall 250mph.

Also in the movie the fall rate would have been increase as soon as the two jumpers were docked one on top of the other. this is double the mass with the same surface area since they were basically stacked on top of each other. Therefore the 90 sec freefall is even more impossible.

The freefall conversation I beleive might be possible in a face to face position. I can talk to students in freefall and they hear me. I believe if they were facing me I could hear them.

As for the two myths they didnt test....here are my answers to that

With the speed at which those two were falling, holding on during openening would be basically impossible. parachutes are designed to open at around 120mph, even at that speed holding on is unlikely. If you did manage to hold on during the initial shock, you would likely be so injured that you couldnt continue to hold on for any lenght of time. On the other hand if its done at subterminal like immediately after exit, then yes a person can hold on. Its still pretty hard though.


If the parachute survived the opening shock from that weight at that high speed without broken lines or rips. then yes it would support and fly with that much weight. The danger would be the stress of that opening.

Yes, you can hold on to the person when the parachute opens.

The parachute would still be able to support that amount of weight, but if you noticed, they did not hit the ground in a "soft landing" either.

The free fall myth was not done correctly.

The dummy was falling out-of-control. Anyone who has sky-dived before knows that with a flat stance,air resistance slows down the fall speed considerably. The dummy had no control on his fall and just fell to his doom.

With the correct free-fall stance you can slow down fall speed and stay in the air longer.

Please revisit.

I have a bit of a question with the part where Grant falls from the airplane to hopefully have a conversation.
It showed that Grant was unable to hear the other guy saying "Pull my finger and you'll hear a tuba." : snickers: that's pretty funny hehehe...

Anyways.. Now in point break.. wasn't Patrick and Reeves[ spelling on that please?] Clinging to each other WHILE also facing each other?
Now the guy talking to grant Wasn't clinging to Grant when he asked the question...

Wouldn't it have made more sense for Grant to face the guy that was 'Shuuting with him and have th guy ask him the question? I dunno.. it just didn't seem Quite authentic enough for me guys.. Any input on this?

A redo of this would not only be quite appreciated, but grant nervous as all heck is rather funny..

My favorite part was watching Rescue Randy hit the ground.

Altimeters are set at the beginning of each flight. They must be reset for different weather conditions, because they do use pressure and from watching the weather report, it can be seen the pressure might be different at your destination. They read altitude above sea level, and you need to subtract ground level to get altitude above ground level, or AGL as mentioned already.

If they wanted 8000 feet above sea level, it could be less than 8000 AGL, and less time to fall, not more. It is usually AGL that is meant when not specified, since it's safer to make an assumption of more space than less.

For a person free falling in spread-eagle position assume the following: weight of 77.1 kg; coefficient of drag of 1.4; flat plate area of 0.548 m^2; air density of 1.225 kg/m^2.

I put a spreadsheet together that numerically integrates the equation of motion using the net forces of gravity and aerodynamic drag. A person will fall 4000 feet in about 30.4 seconds. He (since the weight is more representative of a he than a she) will reach a terminal velocity of of about 89.7 miles per hour. He'll reach that speed in about 14.5 seconds, having fallen about 1900 feet.

Of course, a better model will show increasing density of air as the skydiver descends and this is using about the maximum credible coefficient of drag.

It's fun to play with the parameters in the spreadsheet and see how varying the area, drag coefficient, weight, etc. varies the outcome.

Since, for some reason, I don't have permission to edit my posts, I'll just continue. I plugged values into my spreadsheet for a maximum speed descent - flat plate area of 0.06 m^2 (picture diving into a swimming pool) and drag coefficient of 0.6. This results in a terminal velocity on the order of 392 miles per hour reached after about 60 seconds and a fall of 37,000 feet. Of course, this sort of distance makes it that much more necessary to include the decreased air density at altitude in the model. The density at 18,000 feet is approximately 1/2 that at sea level. I'll work on that and post again.