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That "droppy" feeling

 

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CSpenceFLY  (D 25252)

May 7, 2012, 11:32 AM
Post #26 of 102 (1359 views)
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Re: [michaelmullins] That "droppy" feeling [In reply to] Can't Post

Mike, I love it when you pipe up and blow away all of the bullshit.


michaelmullins  (D 1643)

May 7, 2012, 11:41 AM
Post #27 of 102 (1355 views)
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Re: [JackC1] That "droppy" feeling [In reply to] Can't Post

In reply to:
In reply to:
Horizontal acceleration/deceleration and vertical acceleration/deceleration are totally independent events and one does not affect the other.

Not quite. Aerodynamic drag doesn't care which direction the wind is coming from, it only cares about the magnitude of it, squared. This mixes up the two components of acceleration so the horizontal component of drag will affect the vertical acceleration due to gravity and this produces a slight amount of lift. Take two identical jumpers, one in a balloon and one in a plane, exiting at the same time. The jumper from the balloon will find themselves at pull time a couple of seconds sooner than the one from the plane due to this effect. It's a well know physical phenomenon.

Granted. However, the purpose of this discussion was the analysis of the sensation the jumper experiences. The aerodynamics you discuss, while correct, do not alter the sensation and explanation of same.

Mike


JohnRich  (D License)

May 7, 2012, 11:42 AM
Post #28 of 102 (1354 views)
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Re: [peregrinerose] That "droppy" feeling [In reply to] Can't Post

In reply to:
Have you ever dropped out of a bomb bay door? There is no wind. You are completely sheltered. There is no way to tell that the plane is moving or if it is standing still... it 'feels' still because you're completely inside. Then you drop out, just like a balloon.

You are inventing definitions of 'acceleration.' By your definition, you would feel acceleration going around the corner in your car due to change of direction, which clearly you do not. I am using a physics definition of acceleration, which is independent of direction.

I'm not sure why you're so hell bent on 'proving' that you just get used to a sense of falling from a plane, when it clearly doesn't exist and both the physics and the biology state otherwise, but hey, if it makes you happy, have at it Smile

A bomb bay door isn't any different from a tailgate.

I'm not inventing any definitions, I'm just explaining the different ways that some people seem to be using that term. And in order to understand what they're talking about, we have to know how they mean "acceleration".

I'm not hell bent on proving anything. I'm just trying to understand the phenomenon. And so far what I'm getting is that it's a combination of certain physical conditions, combined with our human physiology.


JohnRich  (D License)

May 7, 2012, 11:46 AM
Post #29 of 102 (1347 views)
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Re: [michaelmullins] That "droppy" feeling [In reply to] Can't Post

In reply to:
Granted. However, the purpose of this discussion was the analysis of the sensation the jumper experiences. The aerodynamics you discuss, while correct, do not alter the sensation and explanation of same.

As a jump pilot, when the last of the jumpers are out the door, and you push the yoke to dive towards the ground, do you get the "droppy" feeling from the lessened G forces when you start your dive and accelerate vertically?


michaelmullins  (D 1643)

May 7, 2012, 11:46 AM
Post #30 of 102 (1346 views)
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Re: [CSpenceFLY] That "droppy" feeling [In reply to] Can't Post

In reply to:
Mike, I love it when you pipe up and blow away all of the bullshit.

It is a dirty, rotten, thankless job but someone has to do it, grasshoppa.

Mike


peregrinerose  (D 28983)

May 7, 2012, 11:52 AM
Post #31 of 102 (1341 views)
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Re: [JohnRich] That "droppy" feeling [In reply to] Can't Post

In reply to:
In reply to:
Have you ever dropped out of a bomb bay door? There is no wind. You are completely sheltered. There is no way to tell that the plane is moving or if it is standing still... it 'feels' still because you're completely inside. Then you drop out, just like a balloon.

You are inventing definitions of 'acceleration.' By your definition, you would feel acceleration going around the corner in your car due to change of direction, which clearly you do not. I am using a physics definition of acceleration, which is independent of direction.

I'm not sure why you're so hell bent on 'proving' that you just get used to a sense of falling from a plane, when it clearly doesn't exist and both the physics and the biology state otherwise, but hey, if it makes you happy, have at it Smile

A bomb bay door isn't any different from a tailgate.

I'm not inventing any definitions, I'm just explaining the different ways that some people seem to be using that term. And in order to understand what they're talking about, we have to know how they mean "acceleration".

I'm not hell bent on proving anything. I'm just trying to understand the phenomenon. And so far what I'm getting is that it's a combination of certain physical conditions, combined with our human physiology.

Acceleration is a physics term. It has one definition. Any other definition is invented. Acceleration is not related to direction. If you are going to relate it to direction, you are inventing a definition.

You have a preconceived notion that the sense of falling is something you adapt to, you are not seeking understanding, you are seeking validation of your viewpoint. Very different things.

Read up on the vestibular system and physics, as I've tried to give quick and simple summaries of both, but it seems that you need more. I just don't have the time or interest to teach either topic via internet.


michaelmullins  (D 1643)

May 7, 2012, 11:56 AM
Post #32 of 102 (1337 views)
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Re: [JohnRich] That "droppy" feeling [In reply to] Can't Post

In reply to:
In reply to:
Granted. However, the purpose of this discussion was the analysis of the sensation the jumper experiences. The aerodynamics you discuss, while correct, do not alter the sensation and explanation of same.

As a jump pilot, when the last of the jumpers are out the door, and you push the yoke to dive towards the ground, do you get the "droppy" feeling from the lessened G forces when you start your dive and accelerate vertically?

Any pilot who pushes the yoke forward will experience a less than positive g, depending on how fast and far you push the yoke forward. However, you can always cancel less than positive g with positive g. A roll into a steep bank will pull more than level fight positive g and it will cancel out the push forward and the net effect can be 1 G, or whatever you wish depending on the manipulation of the controls.

Mike


JohnRich  (D License)

May 7, 2012, 12:15 PM
Post #33 of 102 (1324 views)
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Re: [peregrinerose] That "droppy" feeling [In reply to] Can't Post

In reply to:
Acceleration is a physics term. It has one definition. Any other definition is invented.

Understood, but at least one person seems to be using that term in a different sense, and if you try and interpret his statement using the actual definition, then you won't understand what he's saying. So I'm not saying we should invent new definitions, but I am saying that we have to understand the viewpoints that people have based upon their own personal definitions.

In reply to:
You have a preconceived notion that the sense of falling is something you adapt to, you are not seeking understanding, you are seeking validation of your viewpoint. Very different things.

Not seeking validation. It's simply a theory I've put forth for discussion. Our brains adapt to a great many things from repeated exposure to those things. In skydiving, we learn to overcome our fear of falling. We develop an innate sense of timing so that we know when it's break-off time without looking at our altimeters. Our brains no longer recognize the loud wind noise because it's tuned out. Oh it's still there all right, but we don't "hear" it any more because it's a distraction, in the same way that a husband tunes out a nagging wife. Perhaps it's also possible to adapt to that droppy feeling. Maybe, just like that wind noise, we learn to tune-out the droppy feeling and just don't notice it any more.


(This post was edited by JohnRich on May 7, 2012, 2:16 PM)


popsjumper  (D 999999999)

May 7, 2012, 1:17 PM
Post #34 of 102 (1303 views)
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Re: [justme12001] That "droppy" feeling [In reply to] Can't Post

You sent the following to jakee:

In reply to:
explain please!!

LaughLaughLaugh
LaughLaughLaugh
LaughLaughLaugh

You don't know jakee at all, do you?
LaughLaughLaugh


justme12001  (D 29862)

May 7, 2012, 1:58 PM
Post #35 of 102 (1288 views)
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Re: [popsjumper] That "droppy" feeling [In reply to] Can't Post

nope, not at all. I started to write something with some sarcasm, which I was kinda hoping was what his/her comment was, then I erased it and just wrote the explain Smile


jakee  (C License)

May 7, 2012, 2:57 PM
Post #36 of 102 (1265 views)
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Re: [justme12001] That "droppy" feeling [In reply to] Can't Post

In reply to:
explain please!!

1) You do accelerate significantly when jumping from an aeroplane.

2) You do not have 'wind resistance' inside a plane.

3) Your inner ear is not adapted to 90mph inside a plane, it's adapted to steady state, ie. no acceleration.

4) An balloon may not be accelerating on jump run but neither is an aircraft.

5) Vertical acceleration from an aircraft is the same as vertical acceleration from a balloon.


jakee  (C License)

May 7, 2012, 3:03 PM
Post #37 of 102 (1263 views)
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Re: [peregrinerose] That "droppy" feeling [In reply to] Can't Post

In reply to:
Jakee, it is neither confused nor contradictory, just overly simplified for the non-physiologists of those on here, which I would guess is almost everyone.

And most everyone is also not a physicist.

In reply to:
Even if you go around a corner (changing direction), you don't feel a change in velocity, only a change in direction.

Wrong, both in definition and meaning. Velocity is a vector, you are confusing it with speed. Going round a corner at a steady speed is a change in velocity and what you are feeling is acceleration, just like when you hit the gas or the brakes.

In reply to:
Same with skydiving. Feeling a change in direction from a plane (riding the hill) is not the same as the 'falling' sensation (a change in velocity) that you get from a ballon/heli.

Again, riding the hill in skydiving is a change in velocity (in fact a larger one overall than falling from a stationary balloon). The external references will be different, but the inner ear will detect the acceleration just the same.


jakee  (C License)

May 7, 2012, 3:06 PM
Post #38 of 102 (1262 views)
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Re: [peregrinerose] That "droppy" feeling [In reply to] Can't Post

In reply to:
You are inventing definitions of 'acceleration.' By your definition, you would feel acceleration going around the corner in your car due to change of direction, which clearly you do not. I am using a physics definition of acceleration, which is independent of direction.

I'm sorry, but you clearly do and you are plainly not, respectively.

I would advise you to look up the definitions of velocity and acceleration before you get too entrenched in this argument. It's for your own good.


jakee  (C License)

May 7, 2012, 3:08 PM
Post #39 of 102 (1260 views)
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Re: [peregrinerose] That "droppy" feeling [In reply to] Can't Post

In reply to:
Acceleration is a physics term. It has one definition. Any other definition is invented. Acceleration is not related to direction. If you are going to relate it to direction, you are inventing a definition.

Too late. You don't know it yet, but that's going to hurtSly


(This post was edited by jakee on May 7, 2012, 3:11 PM)


theplummeter  (C License)

May 7, 2012, 3:37 PM
Post #40 of 102 (1249 views)
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Re: [jakee] That "droppy" feeling [In reply to] Can't Post

Two weeks ago I jumped out of a Cessna at 75mph and then an Otter at 95 knots (109mph) two days later. The Cessna jump felt "droppier" for lack of a better term. Otter to balloon the next day felt like a staggering difference, and now having returned to the Cessna it again feels like a greater acceleration.

Without getting into too much theoretical physics I think the difference in speed between jump run and free fall is perceptible.


peregrinerose  (D 28983)

May 7, 2012, 3:47 PM
Post #41 of 102 (1239 views)
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Re: [jakee] That "droppy" feeling [In reply to] Can't Post

You are right, acceleration is a vector. However the inner ear/vestibular system does not change that. Think about RW... you are clearly moving, in freefall, and have absolutely no sense of that. You are flying with other people.... no sense of falling. Even when tracking, you have changed direction, still no sense of falling despite adding horizontal vectors.

It doesn't hurt. I'm human, I am not a physicist, I'm allowed to be wrong, and I admit to it when I am.


michaelmullins  (D 1643)

May 7, 2012, 3:48 PM
Post #42 of 102 (1237 views)
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Re: [theplummeter] That "droppy" feeling [In reply to] Can't Post

In reply to:
Two weeks ago I jumped out of a Cessna at 75mph and then an Otter at 95 knots (109mph) two days later. The Cessna jump felt "droppier" for lack of a better term. Otter to balloon the next day felt like a staggering difference, and now having returned to the Cessna it again feels like a greater acceleration.

Without getting into too much theoretical physics I think the difference in speed between jump run and free fall is perceptible.

I have explained the sensation in an earlier post in this thread but here it is again:

Here is the correct answer:

When a skydiver leaves the aircraft in horizontal flight he has the full horizontal speed of the aircraft at the instance of exit. The skydiver will then decelerate horizontally while accelerating vertically. Horizontal acceleration/deceleration and vertical acceleration/deceleration are totally independent events and one does not affect the other. For example, if you place a rifle horizontally to the earth (assuming for this discussion that the earth is perfectly flat) and fire the rifle while simultaneously dropping a bullet the same distance that the rifle is above the ground, both bullets will hit the ground at the same exact time. Vertical velocity due to the pull of gravity is always independent of horizontal velocity.

When a skydiver leaves an aircraft with horizontal velocity he decelerates horizontally while accelerating vertically. These forces of acceleration and deceleration cancel one another and your body does not feel the "zero G" sensation. The slower the aircraft exit speed, the more likely you are to feel the vertical acceleration. In a balloon or hovering helicopter with zero horizontal airspeed you will feel the full vertical acceleration.

In summary, the slower the aircraft exit airspeed the more likely you are to feel the zero G sensation.

Mike Mullins


peregrinerose  (D 28983)

May 7, 2012, 3:53 PM
Post #43 of 102 (1234 views)
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Re: [jakee] That "droppy" feeling [In reply to] Can't Post

In reply to:
In reply to:
explain please!!

1) You do accelerate significantly when jumping from an aeroplane.

2) You do not have 'wind resistance' inside a plane.

3) Your inner ear is not adapted to 90mph inside a plane, it's adapted to steady state, ie. no acceleration.

4) An balloon may not be accelerating on jump run but neither is an aircraft.

5) Vertical acceleration from an aircraft is the same as vertical acceleration from a balloon.

1. Tell that to your vestibular system... that really notes no appreciable difference in speed. 90mph one way slowly transitioning to 120 as you ride the hill is not noted by any real change.

2. Unless you suddenly materialize in the air somehow, that split second you cross the threshold of the door, you are at zero mph down, and 90mphish horizontally, and have wind resistance.

3. Yep... your inner ear is adapted to the steady state of 90mph, just like 90mph in a car, and no sense of speeding up when you go around a corner at the same 90mph. If you hit the breaks and go around the corner, you notice the change in speed, but not in a steady state change... just like changing direction in freefall.

4. Nope, aircraft is not accelerating. Which is why you are adapted to the steady state of being in motion, and no change of steady state of being in motion when exiting an aircraft, whereas there is a change of steady state motion from heli/balloon.

5. Yep, but as you pointed out, acceleration is a vector, not just one component... so acceleration from a balloon vs. aircraft is not the same, correct? The vectors are different.


jakee  (C License)

May 7, 2012, 4:04 PM
Post #44 of 102 (1229 views)
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Re: [peregrinerose] That "droppy" feeling [In reply to] Can't Post

In reply to:
Think about RW... you are clearly moving, in freefall, and have absolutely no sense of that.

Why would you? Movement is not acceleration and your inner ear has no part in it.


(This post was edited by jakee on May 7, 2012, 4:05 PM)


Premier billvon  (D 16479)
Moderator
May 7, 2012, 4:08 PM
Post #45 of 102 (1225 views)
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Re: [lookoutbelow] That "droppy" feeling [In reply to] Can't Post

>if it is something you just get used to and just stop noticing

It's something you just get used to.

While you were inside the plane you experienced a constant 1G (32 feet per second squared) acceleration due to gravity. The bench (and the airplane's wings) resists the force caused by gravity; thus you feel an acceleration upwards as your body resists this force. This is what we all experience every day of our lives. Note that if you were in zero-G and were in a ship that was accelerating at 1G it would feel exactly the same; there would be no way to tell from how it felt that you were on a ship instead of on a planet.

So inside the plane you experienced a feeling of 1G upwards. That acceleration is a vector, which means it has two components - a magnitude (1G) and a direction (upwards.)

Now you dive out of the plane. For the split second that your feet leave the door but you are not exposed to the wind, you are in "true" freefall - falling towards the ground, accelerating at 32 feet per second. Again, we are all used to this feeling; anyone who jumps into a pool or even off a curb experiences this for a fraction of a second.

Now you hit the relative wind. The drag starts accelerating you backwards, trying to slow you down to zero speed with respect to the wind. That's an acceleration of about 10 feet per second, and you feel it acting towards the tail. That means you are feeling 1/3 of the gravitational force you usually feel and it is in an unusual direction. This is perceived by many as a feeling of falling.

As the wind decelerates you you also start to pick up speed towards the ground. This increases your speed. As drag builds up your acceleration upwards increases, acting against the force of gravity pulling you downwards. After ten seconds or so the magnitude of the acceleration is back at 32 feet per second (normal gravity) and the direction is up (normal gravity.) It now feels, from an acceleration perspective, like you are lying on the ground.

Once you have a bunch of skydives you get used to the few seconds of decreased acceleration and you don't notice it any more - unless it changes. During World Team we'd make 10-20 jumps out of C130's whose exit speed was around 150mph, so you would exit and feel MORE than your normal weight as your body was accelerated by the relative wind at two gravities (around 64 feet per second squared.) When I got back to the US I made a jump out of an Otter and felt like I was falling. I had gotten so used to those 2G's on exit that 1/3G was very noticeable. It went away after a few jumps.


(This post was edited by billvon on May 7, 2012, 4:10 PM)


jakee  (C License)

May 7, 2012, 4:21 PM
Post #46 of 102 (1212 views)
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Re: [peregrinerose] That "droppy" feeling [In reply to] Can't Post

In reply to:
1. Tell that to your vestibular system... that really notes no appreciable difference in speed. 90mph one way slowly transitioning to 120 as you ride the hill is not noted by any real change.

You're still thinking about it wrong. Your vestibular system does not measure 'speed'.

In reply to:
3. Yep... your inner ear is adapted to the steady state of 90mph, just like 90mph in a car, and no sense of speeding up when you go around a corner at the same 90mph. If you hit the breaks and go around the corner, you notice the change in speed, but not in a steady state change... just like changing direction in freefall.

No, your inner ear is adapted to steady state. Doesn't matter if it's steady 90mph, steady 0mph or steady 20,000mph. Unaccelerated is unaccelerated.

Now if you get into your hypothetical car, leave your seatbelt off and drive round a sharp corner at a constant 90mph, you can debate whether you are undergoing acceleration while your head is bouncing off the hypothetical window. You said you could admit when you were wrong, this is what you're wrong about.

There is no such thing as a steady state change. A change in vector is an acceleration. It is the non-invented definition of acceleration.

In reply to:
4. Nope, aircraft is not accelerating. Which is why you are adapted to the steady state of being in motion, and no change of steady state of being in motion when exiting an aircraft, whereas there is a change of steady state motion from heli/balloon.

As above.

In reply to:
5. Yep, but as you pointed out, acceleration is a vector, not just one component... so acceleration from a balloon vs. aircraft is not the same, correct? The vectors are different.

Yep, but not in the way you think.

Your reply to point #2 is where it's at (I only nitpicked because you phrased the point poorly). It's going to be to do with how your brain edits together the feedback it's getting from its balance sensors and its external sensory inputs and uses them both to figure out what the hell is going on.


(This post was edited by jakee on May 7, 2012, 4:26 PM)


Quagmirian  (A 110392)

May 7, 2012, 5:01 PM
Post #47 of 102 (1198 views)
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Re: [JohnRich] That "droppy" feeling [In reply to] Can't Post

Acceleration is a change in velocity; both acceleration and velocity are vector quantities, they must have both magnitude and direction. A body moving at speed in any direction which changes direction must experience acceleration in the change of direction. This is A level physics people. Even wikipedia knows it, and no, that's not my source.

Anyway, I got a massive dropping sensation on my first static line jump, but never since then, on any kind of exit or body position. Aerodynamics tells us, like above, that a body falling from a moving aircraft will simply not accelerate as fast as a body falling from a fixed object. The 'two bullets' thought experiment doesn't help us here because it ignores the powerful effects of aerodynamic lift and drag. I may as well say that the tracking position has no effect on my forward speed, or the head down position on my terminal velocity.


Austintxflight

May 7, 2012, 8:09 PM
Post #48 of 102 (1159 views)
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Re: [Quagmirian] That "droppy" feeling [In reply to] Can't Post

We are 6 pages away from descending into a existential discussion on the nature of reality having to do with the droppy feeling.

This shit is thrilling
http://images4.wikia.nocookie.net/...riller-popcorn-o.gif


theplummeter  (C License)

May 7, 2012, 8:42 PM
Post #49 of 102 (1148 views)
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Re: [michaelmullins] That "droppy" feeling [In reply to] Can't Post

In reply to:
In reply to:
Two weeks ago I jumped out of a Cessna at 75mph and then an Otter at 95 knots (109mph) two days later. The Cessna jump felt "droppier" for lack of a better term. Otter to balloon the next day felt like a staggering difference, and now having returned to the Cessna it again feels like a greater acceleration.

Without getting into too much theoretical physics I think the difference in speed between jump run and free fall is perceptible.

I have explained the sensation in an earlier post in this thread but here it is again:

Here is the correct answer:

When a skydiver leaves the aircraft in horizontal flight he has the full horizontal speed of the aircraft at the instance of exit. The skydiver will then decelerate horizontally while accelerating vertically. Horizontal acceleration/deceleration and vertical acceleration/deceleration are totally independent events and one does not affect the other. For example, if you place a rifle horizontally to the earth (assuming for this discussion that the earth is perfectly flat) and fire the rifle while simultaneously dropping a bullet the same distance that the rifle is above the ground, both bullets will hit the ground at the same exact time. Vertical velocity due to the pull of gravity is always independent of horizontal velocity.

When a skydiver leaves an aircraft with horizontal velocity he decelerates horizontally while accelerating vertically. These forces of acceleration and deceleration cancel one another and your body does not feel the "zero G" sensation. The slower the aircraft exit speed, the more likely you are to feel the vertical acceleration. In a balloon or hovering helicopter with zero horizontal airspeed you will feel the full vertical acceleration.

In summary, the slower the aircraft exit airspeed the more likely you are to feel the zero G sensation.

Mike Mullins

Mike,

We're on the same page here. I was just offering a direct comparison of how some jumps felt after having jumped from three different aircraft in a few days.


labrys  (D 29848)

May 7, 2012, 10:40 PM
Post #50 of 102 (1126 views)
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Re: [JohnRich] That "droppy" feeling [In reply to] Can't Post

Quote:
Quote:

"There is little or no "droppy feeling" associated with skydiving from an airplane. That feeling comes from acceleration. Going from a slow speed to fast, etc. When you jump from an airplane going 80-90 mph, you're already going that fast when you exit. Speeding up to 120 mph over the next 10 seconds doesn't create much of a "droppy feeling"

Yeah, I said that.

Let's give it some context from the original thread. Someone said, to paraphrase, that they hated the "droppy feeling" from roller coasters and expected it to last 30 seconds on a skydive.

My response was an attempt at a brief and simple explanation of why that wasn't going to be the case, or at least there would only be a little bit of that sensation in the first 10 seconds or so. Mr Mullins has explained this in detail now.


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