Lose Your Stomach

[nshaver2 0]

Someone was asking me the other day if you lose your stomach when you skydive (like on roller coasters)?. I told them that it doesn't happen when you jump from a plane, or at least hasn't for me, but I was unsure if I was correct on the reason behind it. I told them that when you jump from a plane you don't get that sensation because initially you are moving forward at a faster rate than you are falling. I told them if you jump from a stationary object like a helicopter, balloon, or a base jump that you might get that losing your stomach sensation, which is what some people have told me, but can't confirm because I haven't done any of those types of jumps. I said it was because there is no forward motion just downward. Is this correct? Just curious if I told them right. Thanks

[darkwing 4]

Whatever the reason, I think it doesn't happen in the vast majority of cases.

-- Jeff
My Skydiving History

[labrys 0]

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I said it was because there is no forward motion just downward. Is this correct? Just curious if I told them right.

The "lose your stomach" feeling is caused when your body accelerates. When you jump from a moving object you're going as fast as it is the instant you exit. If it's going slower than your terminal velocity, you'll accelerate to TV but it isn't as noticeable as when you go from zero to TV.

It doesn't really matter that you are moving forward, just that you are moving. Imagine exiting from a plane that was diving straight down at 120 MPH. You wouldn't get that feeling then either.

Owned by Remi #?

[kimemerson 7]

Just a guess because a guess is all I have: I imagine the feeling you get in an elevator or roller coaster could be because the vehicle you're in (elevator or roller coaster car) moves away from the body at first while the body remains where it is until it catches up to the vehicle. At first, your body isn't even registering the movement or the vehicle leaving the scene. In skydiving we are dealing with gravity immediately and it is our bodies doing all the moving. Or something like that. Just a guess. How'd I do?

[wolfriverjoe 1,346]

It's a combination of the forward motion and the downward motion, combined with the air resistance that keeps your inner ears from feeling the acceleration.

Kallend had the best explanation Here.

Some people say they feel it, but I never do.

"There are NO situations which do not call for a French Maid outfit." Lucky McSwervy

"~ya don't GET old by being weak & stupid!" - Airtwardo

[BUBLHED 0]

The answer I give to this question is. In order to "lose your stomach" you need a combination of two or more movements as in the up and sudden down of a roller coaster. When the movement doesn't constitute a sudden reversal as in skydiving or going off of a diving board you don't get that feeling. Most people can relate to this as most have at least jumped from a diving board or the side of a pool. If your pilot is in a climb and suddenly pitches down you can get that feeling, but when jumping the general change in direction is just downward, like running and jumping from a diving board. I personally think that feeling is the result of negative g's which aren't experienced in a jump whether from a plane of a cliff.

ATTACK LIFE ! IT'S GOING TO KILL YOU ANYWAY!!!!

[councilman24 36]

It's simpler than that. What you feel is a change in acceleration. Acceleration is both change in DIRECTION and change in speed. A roller coster is changing direction so you feel it. In skydiving your under constant acceleration of gravity. No change in direction or speed. It could be argued that on exit there is a change. But there isn't. Gravity is acting on you in the plane also. There just is a counter force of the lift of the plane.

I'm old for my age.
Terry Urban
D-8631
FAA DPRE

[JohnMitchell 14]

If you jump from a stationary aircraft with no forward speed, think balloon or hovering helicopter, you will get that weightless roller coaster feeling. It lasts for several seconds, until you build up downward speed that air resistance presents a force against you. Then you "feel" gravity again. When you jump out of a plane in forward flight, you would feel weightless except that the relative wind blowing past the door accelerates you backwards. This acceleration moves your gravity vector forwards, towards the front of the plane. This is why formations fly "on the hill." This acceleration moving the gravity vector is the same effect that spills your beer to the side when you go around a corner in your car, or spills forward when you hit the brakes hard. As you burn off your forward throw and build up downward velocity, the gravity vector moves to point, once again, to the planet underneath you.

Even in orbit in outer space, you're still under gravity's sway. Slow down in your orbit a little too much, and you'll soon reenter the Earth's atmosphere, where you'll find plenty of G-forces. Once again, those G-forces will be the opposite of the wind vector. That's why the astronauts in capsules are pushed back into their couch seats, not squished down into their boots.

Gravity is a curious "force". We only feel it when we resist it, whether sitting a chair, standing on the planet, or falling through an atmosphere. If one is in a vacuum, free to fall, you feel weightless, even if you were accelerating towards the powerful gravity of the Sun. You feel absolutely weightless as the field accelerates you. You only feel weight when you resist the acceleration.

I think Einstein said that gravity is more a curvature in spacetime that we perceive as a force. He also said that the effects of gravity to an experimental observer were indistinguishable from the effects of a uniform acceleration.

This is really how it works. As you can see, I've really spent way too much time thinking about it.

[JohnMitchell 14]

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Acceleration is both change in DIRECTION and change in speed.

Wrong, acceleration can also be a change in velocity or direction only. A dragster certainly accelerates, but it sure doesn't turn. A sharp turn in a car going at a steady speed will certainly accelerate coffee all over your lap.

[simplechris 0]

I didn't get the feeling when I went out of the Otter for my first time. The 2nd time I went of of a Cessna and it was there for a couple of seconds. Someone told me it was bc the 182 moves a lot slower and then some people tell me it's just bc I am anticipating it. Kind of like I'm doing it to myself. I always thought I hated it but it was actually kind of cool. Last weekend they were jumping a heli and they said you could feel from that. Maybe one day I'll experience that if the weather ever allows me to finish student.

[councilman24 36]

by specifiying NO change in direction you have fully specified acceleration. If you only specific rate of change of speed and not rate of change of vector, even if it's zero, you haven't fully specicified the acceleration.

I'm old for my age.
Terry Urban
D-8631
FAA DPRE

[fallfast69 2]

Seems like it has more to do with the "suprise effect" than anyting else. I've never gottin' it from a helicopter, balloon, or aircraft. I think as long as your brain KNOWs exactly when your body is going to drop, it prepares and therefore can avoid you getting that feeling. In an elevator, or as a passanger (sometimes as the driver) going over/down a hill, your brain doesn't know exactly when to prepare the body for the drop.

[JohnMitchell 14]

I love the feeling of weightlessness. I think I'm used to it enough that my stomach doesn't lurch, but I can still feel it happening. Probably some people are more startled than others and are more affected by it, but the physics of it all don't change.

[JohnMitchell 14]

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by specifiying NO change in direction you have fully specified acceleration. If you only specific rate of change of speed and not rate of change of vector, even if it's zero, you haven't fully specicified the acceleration.

Sure, but you said earlier that acceleration was a change in both. """Acceleration is both change in DIRECTION and change in speed. """" Remember that statement? I'm saying if my checking account doesn't go up or down in balance, I've got no change in my money. I merely clarified that acceleration could be a change of speed or vector; it didn't have to be both.

[JohnMitchell 14]

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I didn't get the feeling when I went out of the Otter for my first time. The 2nd time I went of of a Cessna and it was there for a couple of seconds. Someone told me it was bc the 182 moves a lot slower and then some people tell me it's just bc I am anticipating it. Kind of like I'm doing it to myself. I always thought I hated it but it was actually kind of cool. Last weekend they were jumping a heli and they said you could feel from that. Maybe one day I'll experience that if the weather ever allows me to finish student.

You're absolutely correct. It's all in the difference in airspeed on exit. Let's say your terminal velocity on your belly is 110 mph. If you leave an aircraft going that speed in your normal body position, you'll feel a 1 G acceleration backwards. Your inner ear will interpret that as the pull of gravity, only the vector is towards the forward horizon, not straight down.

If you jump out of a slower plane, say 55 mph, you'll feel only 1/4 G, since wind resistance equals the square of the speed. Leave a balloon with no airspeed? Yee haw, weightless until you build up airspeed. A cutaway from a low speed mal has the same rush. Unfortunately, I have more cutaways than balloon jumps.

I once left an aircraft in a fast descent, maybe 150 mph. I could tell the difference in wind blast and G as I slowed down to terminal. It's a pretty simple effect, once you really look at the physics behind it all, certainly not amazing.

[Genego 2]

I wonder if it is related in any way to perception. If I drive down a flat straight kansas highway at 95 mph, after a little while it doesn't seem as if I am even moving. Drive down a side street with cars parked on both sides of the road and the same 95 mph is incredibly fast, a difference of perception. On a roller coaster you are connected to the seat, track, with a tangible perception of height, in freefall as soon as you leave the aircraft, there is nothing to be relative to, nothing to tell you emotionally that you are falling at 120 mph. Just my .02 cents to further muddy the waters this cold Sunday morning (7 degrees)

I live with fear and terror, but sometimes I leave her and go skydiving.

[billvon 2,406]

>I said it was because there is no forward motion just downward. Is this
> correct? Just curious if I told them right. Thanks

Not quite. That feeling you mention is basically zero-gee, or a lack of any forces acting on your body. We spend our entire lives in a one-gee field, and thus are used to the somatic inputs of feeling gravity pull every part of us (our limbs, skin, inner ears, even internal organs) in some direction or the other.

In freefall, we're still feeling one gee. Air is supporting us and preventing us from falling any faster, so the sensation is similar to lying on a mattress, or floating in water. That's because if your exit weight is 200, and you are falling at 120 miles per hour at terminal, your drag gives you exactly 200 pounds of resistance, and that drag provides the force that keeps you from going any faster. You can increase that a bit to fall slower or decrease it to fall faster but not by much.

When you exit an Otter at 80 knots, you have roughly half the drag acting on you that you'd have at 120 miles per hour. So you have the same basic sensation of gravity acting on you, just half the amount. Some skydivers notice this when they first start skydiving and then get used to it. Some are so overloaded that they never notice it until that first few seconds feels normal.

When you exit a balloon at zero mph, you have no drag at all acting on you, and thus you feel no force at all on your limbs, organs, ears etc. That is so outside our normal experience that people use terms like "losing your stomach" to describe it.

Some other thought experiments:

If the balloon basket was cut away from the envelope, and started falling at 80mph, if you exited it would feel very much like an Otter exit in terms of forces you felt. If you could run out the back of a Skyvan at 80kts so you completely counteracted its speed, you'd feel that same falling sensation as you would out of a stationary balloon.

[schmit.paul 0]

John,
Your grasp on classical gravity/forces/acceleration is as finely-tuned as many of my fellow peers in the physics community, so my compliments! I'll offer up a few points to perhaps add a little more clarity to the above discussion:

First, my interpretation of the stomach-in-your-throat feeling is this--your body is set up internally in such a way that frictional forces between your skin/bones/organs and pressure/viscous forces between your blood and blood vessels counteract gravity 100%...if they didn't, your blood and organs would rush down to your feet while you're simply standing on the ground perfectly still. So without any external acceleration of your body, you have the force of gravity pointing down and frictional/pressure-viscous forces pointing up, and they exactly counteract. Now, imagine you now pull the ground out from under you and you go into a feet-first freefall. Under the influence of gravity, every object accelerates at the same rate (Galileo discovered this by showing balls of lead and far-less-dense wood fell at the same rate when dropped from a tower...of course, a lead ball of the same size would have a higher terminal velocity, but this is irrelevant to our discussion). Thus, without the aid of frictional/viscous forces, your body/organs/blood in initial feet-first accelerated freefall would maintain its internal configuration (every part and piece of your body accelerates at the same rate). Thus the two different systems (standing on the ground and accelerated freefall) have different internal equilibria, and when you transition from one to the other your body internally "reconfigures" itself (in the case of jumping, during your ~5 sec on the hill). The new equilibrium includes increased blood flow to your head (since your blood is no longer inclined to pool at your feet, and the pressure gradient in your vascular system is allowed to equilibrate) and likely a slight upward lift and decreased frictional force between your organs and their surrounding infrastructure (for the same reason as your blood--they're no longer being held in place via friction and pressure to fight gravity's tendency to pull them down toward your feet, so naturally there's a recoil effect that points toward your head). Once you reach terminal velocity, this effect ceases and you are once again in an inertial reference frame, as if you were standing on the ground, and your internal system settles back into its original state. The reason I emphasized feet-first freefall is because this is the only time I've ever had the stomach-in-throat experience--skydiving, amusement parks, whatever. I obviously don't get this feeling when I accelerate forwards or backwards in a car/airplane/etc, and accelerating upwards headfirst (identical to diving downward out of a plane headfirst) also doesn't give the same feeling (though this situation has its own unique effect, namely an increased effective gravity that momentarily pulls blood away from your head and increases the pressure of your organs in the direction of your feet).

One last thing I'll mention is that to some extent, your forward movement when jumping out of a plane is not as relevant to the mitigation of the stomach-in-throat feeling as one might think. The equations describing the motion of a body falling through free-space demonstrate an interesting feature--they are dimensionally decoupled. In other words, your horizontal and vertical movements are completely independent...thus a ball released from a moving plane and another ball released from a stationary balloon at the same altitude will hit the ground at the same time, in spite of the differences in horizontal motion between the two balls--the vertical motion is entirely independent. Now, going from a ball to a body makes things more complicated, because reorienting your body produces new forces that couple horizontal and vertical motion (lift and drag), but neglecting this I'd argue that jumping feet first out of a balloon and jumping feet first out of a plane will produce the same initial effect on your body vertically (assuming you could maintain a vertical body orientation in spite of the shifting relative wind on the hill), and you should experience the stomach-in-throat feeling in both instances. As a relative newcomer to skydiving, however, I've learned first-hand that the wind loves to reorient your body almost immediately as soon as you leave the plane, and jumping out of a plane feet-first doesn't always mean you maintain that orientation on the hill.

And John, you're exactly right about Einstein's theory of gravitation. Interestingly, objects tend to move on geodesics (shortest path between two points along a curved surface), which in vacuum without any massive bodies is just a straight line in space, but with mass added winds up forming a curved path through space due to the effect of mass on the curvature of space-time.

Hope that wasn't too ridiculously long-winded, sorry if it was

Paul

[edited for better wording]

"Ignorance more frequently begets confidence than knowledge." ---Charles Darwin

[schmit.paul 0]

Oops billvon, I might have repeated a bit from your post, sorry about the redundancy!

"Ignorance more frequently begets confidence than knowledge." ---Charles Darwin

[darrenspooner 0]

I wish I could lose my stomach!

Don't forget the fight or flight bit. Anxiety reaction means the stomach will have a tendency to want to void itself. Probably helps to explain why newbies get the sensation more than experienced jumpers. They're no longer anxious.

[kallend 1,635]

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It's a combination of the forward motion and the downward motion, combined with the air resistance that keeps your inner ears from feeling the acceleration.

Kallend had the best explanation Here.

Some people say they feel it, but I never do.

Yep. It's just physics.

...

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