Useless Conversation

[Strazos]

I'll take my chances with skydiving, thanks. 

[gryeyes]

You felt the acceleration for about 2 seconds, and then you hit terminal velocity and just take in the view. And then you just hang out once you pull your chute; it's like sitting in a chair, except you're slowly falling from 5000 feet.

It takes 10-15 seconds for a human body to reach terminal velocity (lots of factors just a ballpark number). Your acceleration decreases as you approach terminal velocity so you don't get the roller coaster sensation beyond the initial few seconds.

[Nerf]

Its not even a few seconds, you don't get it all.  You're not accelerating, you're performing a vector roll, the plane is already going 120mph.

[Margalis]

He's a war-weary misogynist sorceror on the wrong side of the law. She's a wealthy nymphomaniac queen of the dead living on borrowed time. They fight crime!

I see a blockbuster action / adventure / romance, say a supernatural Romancing the Stone.

[Endie]

Its not even a few seconds, you don't get it all.  You're not accelerating, you're performing a vector roll, the plane is already going 120mph.

Wut?  Unless the plane is doing that 120mph straight down when you jump (rather you than me) then you are accelerating at a substantial fraction of roughly 10 metres per second per second (drag being the limiting factor).  Your physicist friend maybe meant something else.  Drawing the vector graph and showing the curve you describe in the air doesn't change the vertical scalar element.  Some people (Strazos describes it) do get the falling sensation, some don't, for the same reason that going over a hump-backed bridge sometimes provides it, but probably won't if you are prepared and expecting it: it's largely about anticipation, muscular tension, and perception.

In freefall, skydivers generally do not experience a "falling" sensation because the resistance of the air to their body at speeds above about 50 mph (80 km/h) provides some feeling of weight and direction.
/

I gave up jumping out of planes and off mountains years ago, btw.  It was fun, but too many of the people I knew died, and if you did a lot of probability-based maths in school and uni then you eventually work out the inevitable ending.  Funnily enough, paragliding was the worst for that: longer exposure and more opportunity for flawed skills to kill you, I suppose.  Felt the best, though.

[Murgos]

I would have assumed you didn't feel an acceleration of 9.8m/s^2 because you are always under that acceleration.  On a roller coaster you usually get that feeling just after having gone over a peak, i.e. you were accelerating upwards but instead of a normal parabola the fact that you are strapped in the car pulls you down sooner than would have been your normal apogee so your insides were going up (or straight) while you were being pulled down.

Just guessing though.

[Righ]

Yes, when in free fall, the liquid in the ear labyrinth isn't being moved so there is no sensation of falling being created by that. You can still get a sensation of falling if your eyes detect vertical motion, but that's usually not apparent when most people are intentionally in free-fall. Somebody jumping along with you and pulling their chute first will do it.

[gryeyes]

Wut?  Unless the plane is doing that 120mph straight down when you jump (rather you than me) then you are accelerating at a substantial fraction of roughly 10 metres per second per second (drag being the limiting factor). 

You are also moving horizontally at 90mph so get you get the "cushion" of wind resistance. And then that transitions into vertical movement so you are always above the 50mph threshold. So he is correct but not for the reasons he listed. It also handily explains why you receive the falling sensation when you jump from things that are stationary or the rides that raise you up slowly and drop into pseudo-freefall, both of which create the falling sensation (eyes closed or not).

Its not "free fall" until you reach terminal velocity (I think?) which is 10-15 seconds after you jump, which is a long time.

[Endie]

Argh.. so much bad physics!

I would have assumed you didn't feel an acceleration of 9.8m/s^2 because you are always under that acceleration.  On a roller coaster you usually get that feeling just after having gone over a peak, i.e. you were accelerating upwards but instead of a normal parabola the fact that you are strapped in the car pulls you down sooner than would have been your normal apogee so your insides were going up (or straight) while you were being pulled down.

Just guessing though.

Gravity exerts a force on you.  That is very different from actually accelerating.  Your body can tell the difference.

Wut?  Unless the plane is doing that 120mph straight down when you jump (rather you than me) then you are accelerating at a substantial fraction of roughly 10 metres per second per second (drag being the limiting factor).

You are also moving horizontally at 90mph so get you get the "cushion" of wind resistance. And then that transitions into vertical movement so you are always above the 50mph threshold. So he is correct but not for the reasons he listed. It also handily explains why you receive the falling sensation when you jump from things that are stationary or the rides that raise you up slowly and drop into pseudo-freefall, both of which create the falling sensation (eyes closed or not).

Its not "free fall" until you reach terminal velocity (I think?) which is 10-15 seconds after you jump, which is a long time.

Where to start?  Let's just say that free-fall is the exact opposite of terminal velocity.  Standing on a pavement means that you have reached the terminal velocity of a human body on a sidewalk.  The wrongness of everything (and I really do mean everything, except perhaps your excellent punctuation) in your first paragraph can be explained by that misunderstanding.  Schools' science departments have a lot to answer for :(

As a further pointer, what I said about the difference between vectors and scalars is important to your "cushion" argument.  The wind resistance which leads to you decelerating rapidly in the horizontal plane will have no effect whatsoever on your acceleration on the vertical plane (excepting any very slight and purely coincidental effects of lift, which we can safely discount).

[gryeyes]

Free fall is motion with no acceleration other than that provided by gravity.

I was thinking that it meant falling with no change in acceleration, which would be at terminal velocity.


Maybe im not explaining what i mean very well. My "cushion" arguement is based on what you quoted and upon googling around it seems to be the correct answer. The wind resistance is giving you the illusion of having weight and direction so you don't feel the sensation of falling. That threshold is at 50mph, you jump from the plane and are instantly "feeling" the illusion of weight since you are moving at 90mph horizontally. As your horizontal velocity decreases your vertical descent breaks the 50mph barrier. So at no point do you feel "weightless" since air resistance has been above the threshold the entire time.

This doesn't make sense?

[Endie]

I kinda know what you meant.  And in a discussion of perceptions, especially transitory ones in a stressful environment, it's not easy definitively say that the feelings you describe wouldn't be quite right.  But the terms you're using are kinda different in meaning from how you use them.

Free fall, in this context, is just accelerating towards earth at the full rate caused by its gravitational force upon you.  If there was no atmosphere there would be no "terminal velocity".  Except, of course, the very terminal one on impact  .  Until that impact you would just keep accelerating.

However, when you reach terminal velocity - when the upwards force of the air resistance upon you is exactly equal to the downwards force of gravity - you will feel just as heavy as if you were lying, stationary, on a pavement.  I think you kinda worked this bit out for yourself.  But the problem with your explanation, which tried to account for each of these forces and really wasn't bad at all in that respect, is I think that you've kinda confused acceleration and speed.  Speed doesn't cause the rollercoaster feeling, acceleraton does, and if you could travel along horizontally at the same (decreasing) horizontal speed as the jumper (this is called sharing a frame of reference) you would see him drop at exactly the same rate as if he had jumped from a balloon, the top of a high building, or one of those straight-down rollercoasters that terrify the bejesus out of me.  The initial air resistance for several seconds doesn't stop you plummetting like a rock.

So why do some skydivers report not feeling the "rollercoaster feeling"?  I suspect that it is partly adrenaline, partly tension, and partly the body angle at which the jump is made: the last two elements stopping the rising sensation of internal organs towards the chest cavity.  I wonder if a straight, vertical plummet, stepping out and dropping feet first, might not cause more of teh sensation to occur.

With music from Scottish ambient-experimentalists Boards of Canada, the single most amazing skydive ever, during Project Excelsior.  Much of that jump was made in what was effectively real free-fall, unhindered by all but a trace of atmosphere, from the edge of space.

[gryeyes]

I think i see what the confusion is about. You think im saying your horizontal movement is slowing down the descent. My first explanation could give that impression.

You posted this:

In freefall, skydivers generally do not experience a "falling" sensation because the resistance of the air to their body at speeds above about 50 mph (80 km/h) provides some feeling of weight and direction.

So the drag experienced when moving faster than 50mph regardless of direction counteracts the feeling of "weightlessness". You leave the plane already moving at 90mph so are instantly above the 50mph threshold(speed is irrelevant beyond its relation to drag). This only counteracts the "falling" sensation (not the falling itself!) you would normally experience. If you were not jumping out of a moving plane and instead a stationary building you would have seconds of falling before the drag was great enough, so you would feel weightless for a time.

I'm not implying your horizontal movement is slowing down your descent (cmon now) or doing anything beyond providing drag.The explanation Nerf gave was close to being correct, if for the wrong reasons. I only used the term free fall because the previous poster used it. I was incorrect in its meaning but the term has no bearing on what im saying.

[Sky]

Why does useless conversation suck all of a sudden?

[IainC]

Why does useless conversation suck all of a sudden?

Gravity.

[Signe]

If you are falling from an airplane and you don't have a parachute, you should try to aim for something soft.  Like pillows or fat people.

[Nevermore]

Mix tape

I think I might almost be halfway done with my first pass to weed out the really shitty songs.  The next few passes through the remaining songs should be much quicker.

So, how's that coming along?

[Murgos]

Argh.. so much bad physics!

On a roller coaster you usually get that feeling just after having gone over a peak, i.e. you were accelerating upwards but instead of a normal parabola the fact that you are strapped in the car pulls you down sooner than would have been your normal apogee so your insides were going up (or straight) while you were being pulled down.

Gravity exerts a force on you.  That is very different from actually accelerating.  Your body can tell the difference.

I don't see what's wrong with the idea that you are under an acceleration along a particular vector, your body (organs, fluids and etc...) are accustomed to that motion and that if you change that vector suddenly you feel it in the body parts not rigidly attached to the frame (1st Law).

Some one else posted an observation, "Hey look I don't feel acceleration downward (organs and stuff going upwards relative to your structure) when I step out of a plane."  The hypothesis that you and all your parts are moving under the same force (gravity) so there is no sudden acceleration in a different direction thus no feeling of internal movement would be pretty apparent in a free body diagram. 

That when you are standing on something it's pushing you up and keeping your relative motion neutral has pretty much nothing to do with it.

[Sir T]

All I know is that after seeing Superman the Movie, I too believe a man can fly.

[voodoolily]

I know how to fix this. I made a wedding cake out of doughnuts and roses for some friends of mine.

[Sir T]

Is that before or after you dropped it out of a plane? 

[Signe]

That is exactly the sort of thing you should try and land on because you will probably be peckish after falling so far.  Try not to land on pregnant women even though they look soft and bouncy.  They are not.

[Lantyssa]

I know how to fix this. I made a wedding cake out of doughnuts and roses for some friends of mine.

That is the most awesome wedding cake I have ever seen.

[WayAbvPar]

Is that before or after you dropped it out of a plane? 

Heh.

Only problem I see with the wedding cake is that is a single serving 

[voodoolily]

That is exactly the sort of thing you should try and land on because you will probably be peckish after falling so far.  Try not to land on pregnant women even though they look soft and bouncy.  They are not.

It's true, the belly is tighter and firmer than it looks, not unlike a basketball. Falling into a tower of pink donuts is always a safe bet, though.

That is the most awesome wedding cake I have ever seen.

It was no tower of cupcakes, but it was tasty. 

[Lantyssa]

My friend did red velvet cupcakes for her wedding.  I suffered to show my approval of their union.  It was great all around.  They got married in the butterfly center.

Amusingly, I got to meet her dad a month beforehand because he was the one who performed surgery on my foot.

[Sky]

Speaking of weddings, we are hopefully hiring Cantiga for ours (if I can drag her to the altar, of course). One of our very favoritist bands of all, talked to them about it over the weekend and they're up for it.

Oh, and for your time-wasting pleasure: http://probablybadnews.com/

[Signe]

What is that?  Renaissance Fair music?  No.  I don't believe you.  Really?  Oh dear. 

[Righ]

They are doing their wedding in the style of a Free Credit Report Dot Com advertisement.

[Lantyssa]

If that's the case, then they should do it in the style of Capitol One.  Seems like it would be apropos for Sky.

[Yegolev]

SAP/DB2 Performance Tuning: Better than Chloroform.

[schild]

Speaking of weddings, we are hopefully hiring Cantiga for ours (if I can drag her to the altar, of course). One of our very favoritist bands of all, talked to them about it over the weekend and they're up for it.

That really says everything we need to know about you, in like one post.

[Samwise]

Mix tape

I think I might almost be halfway done with my first pass to weed out the really shitty songs.  The next few passes through the remaining songs should be much quicker.

So, how's that coming along?

I suffered some burnout and got nothing done last week.  Making more progress this week.  I think something is starting to take form.  Still a lot of songs I haven't listened to yet.  There are a fuckton of songs here.

[Strazos]

I should clarify - I did not feel the stomach dip feeling you get from a road or coaster or anything. It actually sort of felt like falling from a height while skiing.

Still pretty damn awesome.

[Lantyssa]

I don't do a lot of rollercoasters, but isn't the premise with many of them that you do a rapid up followed by a more rapid down?  Your insides aren't just accelerated, they're purposefully forced into a rapid change in vector.

[Endie]

I don't do a lot of rollercoasters, but isn't the premise with many of them that you do a rapid up followed by a more rapid down?  Your insides aren't just accelerated, they're purposefully forced into a rapid change in vector.

"Forced into a rapid change in vector" is just a good definition of acceleration, actually!