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adamjenner

Stupid question but oh well

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This may be the DUMBEST whuffo question you've ever heard...but when you're going head down does the blood tend to rush to your head like it does when you're standing on your head on the ground?

just a silly question i've always wanted to know the answer too.:P

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No. Not a stupid question. I have heard it many times over the few years I've been in the sport.

My explanation for this is:
On the ground you are not moving, however gravity is still "pulling" on you so your blood still flows down to your head. While headdown your body is moving downward as well so when your blood is getting "pulled" down so is your body.

I have nothing to back this up outside logic (although sometimes my logic isn't all that)

DJ Marvin
AFF I/E, Coach/E, USPA/UPT Tandem I/E
http://www.theratingscenter.com

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they already gave you the answer... nope.

but just wanted to say... there is no such thing as a "stupid question"... especially in skydiving. ask away. :P



"There are no stupid questions; only stupid people", Mr. Garrison.....

No really that is a funny question but I could see where you get it from, beside the fact that you are moving, you really are only on your head for 50 seconds or so....

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My explanation for this is:
On the ground you are not moving, however gravity is still "pulling" on you so your blood still flows down to your head. While headdown your body is moving downward as well so when your blood is getting "pulled" down so is your body.

I have nothing to back this up outside logic (although sometimes my logic isn't all that)



I've wondered about this too and have yet to hold headdown long enough to expect any head rush if there is any.
I don't know the answer but I do have a physics point to bring up. Gravity is an acceleration. When you're at terminal velocity your body is no longer accelerating due to air resistance (drag) balancing the acceleration of gravity. Your blood doesn't have this drag and is still being affected by gravity. Therefore my spider-senses tell me that your blood would rush to your head in freefall just like the ground. But what do I know.
Maybe the increased heart rate keeps anyone from noticing any blood rush.

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Um, when you have reached terminal the blood will go to your head. This isn't what you would be paying attention to anyways because......well you have more important things to worry about;). Also, like spidermonkey said, I think the increased heat rate would prevent this somewhat.
Flying Hellfish #470

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I agree, after you reach terminal the blood will rush into your head, though most people will say no. When in the air most people can't feel any pressure in the head like they can on the ground when they're head down.

Well most people in this sport probably hit something accidently on exit or in the air pretty hard and they haven't noticed it until they landed. only then it started to hurt them or they found out they're bleeding. Sameway most people can't feel the blood rushing in their had.

It's called adrenaline ! B|
"George just lucky i guess!"

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I've wondered about this too and have yet to hold headdown long enough to expect any head rush if there is any.
I don't know the answer but I do have a physics point to bring up. Gravity is an acceleration. When you're at terminal velocity your body is no longer accelerating due to air resistance (drag) balancing the acceleration of gravity. Your blood doesn't have this drag and is still being affected by gravity. Therefore my spider-senses tell me that your blood would rush to your head in freefall just like the ground. But what do I know.
Maybe the increased heart rate keeps anyone from noticing any blood rush.



I wonder more and more about this, but if your theory of blood rushing AFTER T.V. then how come my face is never red while I am headdown. If the blood rushed to my head then even during the short time of freefall there would be a noticable reddening of the face, yet I have never noticed my face being red from the videos of myself I have watched.

The only thing I can think of to even come close to compare this to, is the Aircraft used to train astronauts. The jet does a parabola and during the zero-g dive the occupants stay weightless relative to the aircraft. They are not affected by drag (like you are saying of blood in the body) However they never seem to speed up despite this lack of drag.

Really I have no clue for sure and I have put way too much thought into this now. :(

DJ Marvin
AFF I/E, Coach/E, USPA/UPT Tandem I/E
http://www.theratingscenter.com

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Before you read this, know that I am not trying to appear as though I am condescending anyone with this post. I have studied quite a bit of physics and this is my best understanding.

Everything in the world is constantly acted upon by the accelerating force of gravity, constantly accelerating. Even sitting completely still, you are accelerating towards the center of the earth, but you are held static by the ground. Acceleration occurs when a body is acted upon by a force that attempts to "move" that body and change either its direction or its speed. Even slowing down, you are accelerating but in the direction opposite of your motion. Also, any change in direction is also considered acceleration. Both these ideas are a common misconception.

When you stand on your head on the ground, your bloods reference frame (or your body) remains still while the blood is still able to move within the piping of your circulatory system. The body remaining still, the blood attempts to move into an equilibrium position as it “loads” your head full as blood “trickles” down, your heart unable to overcome the power of gravity.

In freefall, the reference frame and the blood move together through a fluid, the air. Terminal velocity does hold the body at a fixed speed ultimately, but the reference frame and blood are both still accelerating at the same rate and are still in motion together so everything remains in equilibrium and operates normally. Blood will continually flow normally because the reference frame moves just as quickly as it does. If the reference frame were to be abruptly slowed under a very rapid acceleration, the blood will continue to move and could cause a slight heavy feeling but that is unlikely. It is kind of like riding in a car, the reference frame accelerates and moves along with all of the contents together. If the car strikes and object and the reference frame is slowed or stopped, all the contents not attached, the people inside, continue to move possibly all piling up on the dashboard or going through the windshield. Or picture a toy racetrack inside the car, the toy will travel around the track normally once the car is in motion, unaffected until the car is acted upon abruptly.

I completely agree with DJMARVIN’s explanation and logic.
Premier Member IGPA
2009 IGPA Overall Champion

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Woohoo, a nerdy discussion! B| I actually think about this stuff on the way to altitude. :)
I have to stand by my first answer on this one.

I'm still not sure why it is not noticed. Why aren't belly fliers faces red in freefall from being wind-blown with cold air? Maybe adrenaline has something to do with it, maybe we just don't notice it. Again, I'm just learning to skydive and am no expert, but I am an engineering student and have had my share of physics classes.

The "Vomit Comet" is actually a good example of gravity's acceleration. Let's ignore horizontal movement since gravity only works vertically. Before the plane can experience zero g's for an extended amount of time, it must climb as fast as possible. Then the plane flies in an arc and everyone floats. Why? Imagine throwing a ball straight into the air. You apply a force that gives the ball an initial velocity as it leaves your hand. The instant your hand is no longer supporting the ball, gravity applies a force to accelerate it towards the earth. You can see this acceleration as a decrease in speed up and then an increase in speed back down. Now back to the airplane. The high climb rate is like the ball's initial velocity. The pilot flies the plane in the same arc that gravity would pull an object in, so the plane's climb rate decreases until it is descending rapidly. The people inside the plane experience this acceleration towards the earth just as if they were shot straight up into the air like the ball, the only difference is the wind is blocked by the airplane. (I hope this makes sense, if not I'm sure you can find more info online)

Now think of the people in the airplane as blood cells. When the plane is not accelerating in any direction, where are the people? They are standing on the floor because they still feel the force of gravity but it is counteracted by the floor. When the plane is accelerating due to gravity, so is everything inside and everything will "float."
Or how about this, stand on a scale in an elevator. Your weight will only change as the elevator's speed changes. When you're falling or rising at the same rate your weight will be the same as it normally would be. So being in a moving vessel doesn't necessarily mean the forces on your body will be any different than standing on the ground.
We've also discussed the following scenario in one of my classes. If you drop a hollow sphere that is half full of water, the water will settle at the bottom of the sphere once the sphere reaches terminal velocity. Gravity is a force that acts on anything with mass (every single atom), not just the outside of the sphere.


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Terminal velocity does hold the body at a fixed speed ultimately, but the reference frame and blood are both still accelerating at the same rate and are still in motion together so everything remains in equilibrium and operates normally.


But at TV your body as a whole is not accelerating. There is no force preventing the blood from gathering towards the earth. At least no force besides what is experienced on solid ground (i.e. veins and blood pressure).


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Or picture a toy racetrack inside the car, the toy will travel around the track normally once the car is in motion, unaffected until the car is acted upon abruptly.


Exactly. The toy cars and track and people are being supported by the floor of the car just like the car wasn't moving. The horizontal velocity has nothing to do with gravity, but rather momentum, which is =m*v
If you put wheels on the top of the car everything inside would fall onto the roof since the car is not accelerating perpindicular to the earth (TV).


Phew, class dismissed.
Just kidding! :P I'm pretty sure I understand this right, but I'm no expert.

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Thats a perfect analogy and is completly correct:)
At TV, gravity is acting and trying to accelerate you downwards but wind resistance is a force of equal magnitude but in the opposite direction thus cancelling out the acceleration due to gravity. So.......the net acceleration on your body is zero and you have a constant veloctiy (terminal velocity). However, the blood in your body is not acted on by the wind resistance so it is still accelerated by gravity and will go to your head. Wheew....physics is paying off and yes I do feel quite nerdy right about now.:D
Flying Hellfish #470

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Why aren't belly fliers faces red in freefall from being wind-blown with cold air?




Their faces are white because the cold is restricting bloodflow to the capillaries in the skin -- Just like people look a tiny bit translucent / blue when they are really, really cold.

The redness occurs on the ground, when bloodflow returns to warm the skin back up. Skin irritation from windburn also takes a while to show up.

This can explain why people don't have red faces on video (colder air is restricting bloodflow to the skin), even if they had more blood pooling in their head.

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The instant your hand is no longer supporting the ball, gravity applies a force to accelerate it towards the earth.



I am guessing that you didn't intend to write this statement as you did. (Since gravity applies force to the ball even while it is in your hand.) ;) English can be so ambiguous sometimes.

Increased heartrate, I agree with you, also helps combat any blood pooling.

j

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crestfall is right. It's relativity, kids. Relative to your body's motion, the blood is essentially not feeling any acceleration. Relative to the ground, the blood is feeling an acceleration of 9.8 m/s/s. On the ground tho, your blood feels the same acceleration relative to your body, so the blood rushes to your head. Now try the same question at the speed of light, it gets tricky. :)
Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so. --Douglas Adams

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Terminal velocity does hold the body at a fixed speed ultimately, but the reference frame and blood are both still accelerating at the same rate and are still in motion together so everything remains in equilibrium and operates normally. Blood will continually flow normally because the reference frame moves just as quickly as it does.



I'm with cresTfall on this one. The blood does not pool in your head because in freefall, more importantly/specifically, at Terminal Velocity, you are in a state of equilibrium. Your blood and organs are moving at the same velocity as the "shell" of the rest of your body... Now spread your legs real wide and real quick in HD and that's a different story. The astronauts in your vomit comit had better be buckled up! lol, a rapid upwards acceleration will cause the blood to apparently be pulled down relative to the "shell".

You hear a good HD coach say he/she feels like he/she is 'hanging' by their feet when slowing up using the legs... hang by your feet, get red in the face.

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It is kind of like riding in a car, the reference frame accelerates and moves along with all of the contents together. If the car strikes and object and the reference frame is slowed or stopped, all the contents not attached, the people inside, continue to move possibly all piling up on the dashboard or going through the windshield.



Ever wonder why there is no "Heart in your throat" feeling when leaving the aircraft? It's because you've got horizontal speed on exit which slowly converts to vertical speed. We call it the hill yeah? Like the above example, we are not 'thrown forward' relative to the plane as it keeps moving but we are still thrown forward of the point where we actually parted with the plane. Downwards acceleration is still a constant but with relative speed, your 'innards' tend to stay with you... thusly, no 'heart in the throat'



My Karma ran over my Dogma!!!

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I'm with cresTfall on this one. The blood does not pool in your head because in freefall, more importantly/specifically, at Terminal Velocity, you are in a state of equilibrium. Your blood and organs are moving at the same velocity as the "shell" of the rest of your body... Now spread your legs real wide and real quick in HD and that's a different story. The astronauts in your vomit comit had better be buckled up! lol, a rapid upwards acceleration will cause the blood to apparently be pulled down relative to the "shell".



You guys are very very wrong.

Equilibrium, yes. But you are in equilibrium standing on the ground.
In equilibrium, all forces are in balance. The state of equilibrium has motion at a constant velocity (which might be zero). That's Newtons First Law.

Forget 9.8 meters per second. That's in a vacuum anyway. We've got air resistance to contend with. At terminal velocity, the force of air resistance balances the force of gravity and produces motion at a constant velocity. Sure it's dependent on shape, which is why we can speed up and slow down, but the steady state is constant v.

On the ground, the force of the ground pushing up balances the force of gravity and produces motion at a constant velocity of 0. The situations are identical so long as you aren't accelerating.

And the forward speed of the aircraft doesn't prevent us from having the sinking feeling of falling, except as a way that it fools our body into not noticing. Perpendicular vectors are independent. In the downward direction you accelerate at exactly the same rate regardless of whether you are exiting from a hovering helicopter, an otter at 80knots or a c130 at 160knots.

This is physics 101, people.
Don't post fake science.
Some of us have engineering degrees.

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so...does the fact that you don't feel blood rush to you head while flying head-down in a wind tunnel go against what you are saying or support what you are saying. sounds like it's going against what you are saying...

sorry to bring up an old topic, but i did use the search button.

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so...does the fact that you don't feel blood rush to you head while flying head-down in a wind tunnel go against what you are saying or support what you are saying. sounds like it's going against what you are saying...

sorry to bring up an old topic, but i did use the search button.



You may not feel it in a tunnel for reasons that are unrelated to what causes the heavy feeling when you are upside down. Perhaps you are simply too distracted to feel it. Unless you are accelerating downwards, it is the same as if you had no velocity at all.
People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

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Your blood doesn't know the difference between your body being held up by air, or by the floor.

There is some medical reason for not getting red-faced and not feeling it, but it has nothing to do with your blood falling the same speed as your body. That's silly.

Adrenaline and increased heart rate might be the reason.

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Your blood doesn't know the difference between your body being held up by air, or by the floor.

There is some medical reason for not getting red-faced and not feeling it, but it has nothing to do with your blood falling the same speed as your body. That's silly.

Adrenaline and increased heart rate might be the reason.



I don't understand your reaction to my post. Silly? It is a fact. I think you didn't understand that I was saying that a person should get red faced when on their head.
People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

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