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Woohoo, a nerdy discussion! 
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.
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).
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!
I'm pretty sure I understand this right, but I'm no expert.
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.
QuoteTerminal 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).
QuoteOr 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!
I'm pretty sure I understand this right, but I'm no expert.
haha thanks for the answers guys.
i love nerdy topics
But it's just always been a question in my head.
thanks for the info!
i love nerdy topics
But it's just always been a question in my head.
thanks for the info!
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.
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.
Flying Hellfish #470
Fluid/pump dynamics in an accelerating system.
j
j
QuoteWhy 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.
Quote
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
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.
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goose491 0
QuoteTerminal 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.
QuoteIt 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!!!
apoil 0
Quote
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.
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.
sorry to bring up an old topic, but i did use the search button.
sundevil777 102
Quoteso...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
bqmassey 0
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.
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.
sundevil777 102
QuoteYour 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
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.
2009 IGPA Overall Champion
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