Select to expand quotesotired said..
Well, I guess I want to determine something first; when I breathe in, am I sucking a breath in or is the universe pushing a breathe into me?
Excellent example, in our case sucking doesn't exits in physical sense...
or do exist ?
One may claim that breathing air IN is the active act the require muscles to "suck" the air in, others may claim that you do exhale air actively then air refill your lungs automatically.
We could test this idea experimentally when you stop breathing for a longer period , say for an hour and we check if your chest in the state "inflated" or "deflated"
Select to expand quoteMacroscien said..sotired said..
Well, I guess I want to determine something first; when I breathe in, am I sucking a breath in or is the universe pushing a breathe into me?
Excellent example, in our case sucking doesn't exits in physical sense...
or do exist ?
One may claim that breathing air IN is the active act the require muscles to "suck" the air in, others may claim that you do exhale air actively then air refill your lungs automatically.
We could test this idea experimentally when you stop breathing for a longer period , say for an hour and we check if your chest in the state "inflated" or "deflated"
I did that test, and for an hour it was definitely inflated. I don't have any witnesses, but you can trust me. If I could have captured it at 1000 frames a second it would still prove the same thing.
So, you would argue they are the same thing. Your lungs are trying to expand and as a result any lower pressure area is drawing in air, or the rest of the world is blowing it in.
.. and as the old saying goes, is there such a thing as gravity or does the earth just suck?
Select to expand quotesotired said..
<<<
Well, I guess I want to determine something first; when I breathe in, am I sucking a breath in or is the universe pushing a breathe into me?
I don't think you need to invoke the universe, it's merely the weight of the air above you that's doing the trick.
Select to expand quoteMacroscien said..NotWal said..Macroscien said..
...
if that means that model air plane on International Space Station doesn't have a lift ( in absence of gravity but still plenty of air around ?)
...
Yay, something new :)
I reckon if you threw a model glider in the ISS it would do a back flip and stop.
Remember that my questions are designed not to clarify but confused you ( assuming that you thought that you know already what is going on with sails and airfoils in general) .I guess that my example above points to some weakness in arguments in article ( requirement for gravity to achieve lift)
Where does it say that gravity is required?
Select to expand quotedecrepit said..sotired said..
<<<
Well, I guess I want to determine something first; when I breathe in, am I sucking a breath in or is the universe pushing a breathe into me?
I don't think you need to invoke the universe, it's merely the weight of the air above you that's doing the trick.
haha same mistake as author of this article above, Decrepit. I will ask again , what weight in space suit in the space help you breathing or on ISS??
Select to expand quoteChris 249 said..
Where does it say that gravity is required?
Who ? I don't know . You could check authors name on the link above
Select to expand quoteMacroscien said..
decrepit said..
sotired said..
<<<
Well, I guess I want to determine something first; when I breathe in, am I sucking a breath in or is the universe pushing a breathe into me?
I don't think you need to invoke the universe, it's merely the weight of the air above you that's doing the trick.
haha same mistake as author of this article above, Decrepit. I will ask again , what weight in space suit in the space help you breathing or on ISS??
I think in this case he is responding to my question about whether its the universe, and in this case, just the weight of the air forcing itself into my lungs. Sounds reasonable to me, and nothing at all to do with your discussion on lift.
In a space suit, it is air pressure. On Earth that pressure will be generated from gravity/weight.
Select to expand quoteMacroscien said..
Chris 249 said..
Where does it say that gravity is required?
Who ? I don't know . You could check authors name on the link above
It just seems to be related to the fact that the air in our atmosphere has pressure because of gravity. Without gravity, our air would wander off into space.
However, air doesn't just try to equalise pressures because of gravity (although as said above, the pressure in our atmosphere is created by gravity that stops air from wandering into space). If you flapped a piece of paper inside a space station under zero gravity it won't leave a little hole without air behind it - the air pressure will equalise itself.
Take an inflatable boat or bicycle tire. Push down on the top to displace some air. When you stop pushing, the air will rush back UP from lower down the tire or boat to the top, AGAINST the force of gravity. This is clear evidence (not that it is required) that air will seek to equalise its pressure even against gravity - that's what gives us most of our weather too.
There is no big mystery behind the way a sail works. Many thousands of very smart people have spent many years combining their brainpower and lots of high-tech machinery to work it out.
Something I was taught during my apprenticeship (fitter and turner referring to pumps) " there is nothing that sucks, it creates a vacuum" Or though I beg to differ, cause going to work sucks, nagging women suck, not having enough time for water sports sucks.
So as others have pointed out, low pressures created on one side of the sail (vacuum) high pressure on the other side
Sotired, yes the universe/atmosphere is pushing air into once your muscle's around your lungs relax to allow air to rush in the vacuum in your lungs. The muscles contract to expel/ push the air out.
Select to expand quoteChris 249 said..
However, air doesn't just try to equalise pressures because of gravity
You have this right because once you mentioned gravity- our attention is instantly to Newtonian - gravity law,
and once you talk about gases mechanics that will be more like Robert Boyle domain
Select to expand quoteSupsailDave said..
Sotired, yes the universe/atmosphere is pushing air into once your muscle's around your lungs relax to allow air to rush in the vacuum in your lungs. The muscles contract to expel/ push the air out.
+ 
This seems fairly philosophical, but I'll have a crack 
To me it's about suction, or flow induced by the potential difference between an area of high pressure and low pressure. Air is drawn towards the low pressure zone - suction.
to go off on a tangent, we have SPAC, the soil-plant-air-continuum. Water potential of a fully wetted soil (field capacity) is about -10kpa. as soils dry, the soils water potential becomes more negative. At -1500kpa ( a dry soil), the suction a plant has to apply to extract water from the soil is so great that many plants will die. But the plant isn't really applying suction, it is the atmosphere, acting on the plant leaf. the plant is just a conduit between the soil and the atmosphere. The water potential in the atmosphere is far more negative, -100 Mpa - there's nothing pushing the water vapour there, it's all about suction! Not the same, or is it?
Select to expand quoteStretchy said...
This seems fairly philosophical, but I'll have a crack
To me it's about suction, or flow induced by the potential difference between an area of high pressure and low pressure. Air is drawn towards the low pressure zone - suction.
OK I'm cracking under the weight of this thread
Air isn't drawn or pushed from an area of high to low pressure, it just moves to equalise the pressure. To say it's either drawn or pushed assumes the perspective of an observer at either the low or high pressure zone, no?
Which I suppose means that where you stand on Macro's question depends, well, on where you stand.
Select to expand quoteStretchy said..
This seems fairly philosophical, but I'll have a crack
I love this plant comparison very much 
I do already imagine that I could purchase bag of genetically modified seeds . get into soil, water a bit and in month or so
I have fully grown leaf race sail - 5.0 m
wait a bit and grow to 7.8m2
I am not botanic but I am guessing that cross between banana leaf and bamboo stick ( serving as a mast and battens) could do very well.
Select to expand quoteTristanF said..
OK I'm cracking under the weight of this thread
Don't worry about that.
If you take 5 the greatest physicist walking the planet right now :
say Newton ,Einstein, Stephen Hawking, Micho Kaku, Macro and myusername(loftofwind will do) - and ask the same easy question about airfoils lift -
there will be 7 different explanations.
Everyone explain phenomenon perfectly and exact with that difference that each one will be more distant from truth.
Select to expand quoteTristanF said..
Air isn't drawn or pushed from an area of high to low pressure, it just moves to equalise the pressure.
That is very clever explanation but
think about that
If I was that air pressure - instead of just pushing on the sail ( which is un-penetrable ) - I will simply go around sail and equalize the pressure difference in instant
(?)
Oh gawd. Like said way back by somebody, it is obviously push.
When you have a low pressure area, gas moves from the high pressure area to the low pressure. Why? Not because of a magic vacuum cleaner but rather because the molecules are zipping around in a random way and when there is a pressure differential they go mostly in that direction until things are equalised.
Like if you had a box and all the gas molecules are zipping aound banging into all 6 walls equally. Then u remove a wall. What happens? The ones going that direction escape. End of story.... they were not sucked out, they were pushed that way by their own kinetic energy.
Then after a while just as many are going the OTHER way, so the pressure is equalised.
Think about an inflated balloon and you release the neck. Is any sucking required? No, the high pressure area contains more molecules and unless we are at absolute zero they are jiggling around and they escape due to their own kinetic energy........ not due to being sucked - due to their own kinetic energy. Their own self-generated push.
Select to expand quoteStretchy said..
Water potential of a fully wetted soil (field capacity) is about -10kpa. as soils dry, the soils water potential becomes more negative. At -1500kpa ( a dry soil), the suction a plant has to apply to extract water from the soil is so great
Something absolutely new ! 
That is absolutely nobody mentioned before.If the wet sail have the same speed potential as dry sail ? We drop sails into water very often and once is dry once is wet .
Maybe super wet sail is faster then dry ? or one side dry other wet ?? Can we do one side hydrophobic and another hydrophilic for speed racing competition ? Definitely if you add evaporation equation to our already complex lift calculation , things are getting very complicated. I love it 
Select to expand quoteMark _australia said..
the molecules are zipping around in a random way and when there is a pressure differential they go mostly in that direction unti
I like this molecules analogue, Mark.
Did you played table pool ever Mark . Obviously you did.
So now lets imagine for a moment that our air molecules as big as table pool balls,
Half a kilo each (?)
Forget about all this pressure stuff and imagine that our wind is just a stream of high speed balls hitting our sail.
If our sail is perefectly align along this rain of speeding balls - none hit , none lift
If we tilt our sail and balls start hitting our internal sail ( leward ?? never can remember this lee thing ) they do transfer kinetic energy to our sail and bounce sideways same time.
That will be pure pushing +1, Mark .We just don't need to care about ball flying above, missing our sail.
To answer this question, one needs to understand the following:
(1). Pressure, and
(2). A vacuum.
(1). Pressure
It is defined as Force/Area.
(2). A vacuum
It is defined as a void free of anything. Well, maybe not quite as there is no such thing as a "Pure vacuum".
A vacuum, as the definition suggest, has nothing within it. So if there is nothing, how could there be any force to "suck" the sail forward?
So the only logical explanation remained has to be the positive pressure that pushes the sail forward.
Remember that Cadbury chocolate advert where the fuzzy hair professor Julius Sumner Miller showed us kids how to suck an egg? Well, not quite. His experiment depicts a hard-boiled egg being sucked/pushed into a glass jar, when a piece of paper was burnt within it.
Was it sucked or pushed? It was pushed. The vacuum created by the burning paper that facilitated the egg to be pushed in by air pressure.
Select to expand quoteMacroscien said..TristanF said..
OK I'm cracking under the weight of this thread
Don't worry about that.
If you take 5 the greatest physicist walking the planet right now :
say Newton ,Einstein, Stephen Hawking, Micho Kaku, Macro and myusername(loftofwind will do) - and ask the same easy question about airfoils lift -
there will be 7 different explanations.
Everyone explain phenomenon perfectly and exact with that difference that each one will be more distant from truth.
Einstein tried to do a weirdly-shaped aerofoil once, on a Rumpler (IIRC). The test pilot managed to get it off the ground, was lucky enough to get back on the ground in one piece, and if I recall correctly walked over to Einstein and was close to punching him out.
Einstein wrote later that it was a case where he thought too much, and read too little about what other people had already found out about the problem.
If Einstein couldn't work out airflow and lift, how can we do it? Yes, there are several different valid ways of looking at the issue - the experts who have spent years putting their combined (and very impressive) brainpower together have been saying that for a long time.
What I don't understand is how you can say that "each one will be more distant to the truth". Are you trying to say that you are the genius who has the answer that Einstein and Hawking cannot find?
Select to expand quoteMacroscien said..
Mark _australia said..
the molecules are zipping around in a random way and when there is a pressure differential they go mostly in that direction unti
I like this molecules analogue, Mark.
Did you played table pool ever Mark . Obviously you did.
So now lets imagine for a moment that our air molecules as big as table pool balls,
Half a kilo each (?)
Forget about all this pressure stuff and imagine that our wind is just a stream of high speed balls hitting our sail.
If our sail is perefectly align along this rain of speeding balls - none hit , none lift
If we tilt our sail and balls start hitting our internal sail ( leward ?? never can remember this lee thing ) they do transfer kinetic energy to our sail and bounce sideways same time.
That will be pure pushing +1, Mark .We just don't need to care about ball flying above, missing our sail.
Actually, that is one of the explanations that is shown to be untrue on the NASA site linked to earlier. It is also shown to be untrue by the Einstein "dog leg" upper aerofoil failure mentioned in the previous post. It's also shown to be untrue by anyone who wants to try. Just take a sail and put something to leeward to block the airflow. You will go slower - a lot slower - which shows that we DO need to care about the "balls missing our sail".
NASA shows your theory to be wrong here;
www.grc.nasa.gov/www/k-12/airplane/wrong2.html
The information is out there, and you may as well just read it since you are NOT going to discover something that Einstein was too dumb to work out.
Select to expand quoteChris 249 said..
your theory ...
correction required. 
It is not mine theory. It is just mine interpretation of Mark suggestion.
Because in a minute later I will trying to defending another SBreezer claiming opposite view.
Beside you forger that my goal here is not to explain, but confuse 
If anybody believe that know all physics behind lift, all I am trying to do is seed some doubts, throw you off that post.
Glory for those that keep standing hard.The is illustration of my position here:
All I am doing is trying to know you off of your certainty post. sometimes I win, sometimes I loose
Select to expand quoteChris 249 said.
Actually, that is one of the explanations that is shown to be untrue on the NASA site linked to earlier. It is also shown to be untrue by the Einstein "dog leg" upper aerofoil failure mentioned in the previous post. It's also shown to be untrue by anyone who wants to try. Just take a sail and put something to leeward to block the airflow. You will go slower - a lot slower - which shows that we DO need to care about the "balls missing our sail".
ok you enlighten us what is untrue.
What is your truth then ? We are happy to see your interpretation (if you got any )
sucking , blowing, pushing or pulling, altogether or none. ?
When it comes to choosing we always have limited option , and need to decide on something, then defend it, till you can , then give up and change mind. I guess that will be mine strategy.
Now there is very hard nut to crack for all our pushers and suckers here.
Lets imagine that we take a simple glass pane and water hose.
Lets perform following experiment.
1.- we keep the glass pane at the angle and pour water from hose on to it.
Water obviously spread on the glass and goes down.
2.-Now we till our glass pane to 90 degree, completely vertical.
Most of the water still "stick' to the glass and fall down
3.Now we tilt glass even further and now it is like 270 degree, almost upside down and water stream is still following this glass surface. Upside down!
Should fall off, one may say. What is causing this water to stick to the glass
? Is it glass sucking the water ?, air pressure pushing onto it? vacuum or pressure ? or something else?
Is it related to our sail example or not at all ?
Select to expand quoteChris 249 said..
NASA shows your theory to be wrong here;
and here
and thanks God NASA is always right
Select to expand quoteMacroscien said..Chris 249 said.
Actually, that is one of the explanations that is shown to be untrue on the NASA site linked to earlier. It is also shown to be untrue by the Einstein "dog leg" upper aerofoil failure mentioned in the previous post. It's also shown to be untrue by anyone who wants to try. Just take a sail and put something to leeward to block the airflow. You will go slower - a lot slower - which shows that we DO need to care about the "balls missing our sail".
ok you enlighten us what is untrue.
What is your truth then ? We are happy to see your interpretation (if you got any )
sucking , blowing, pushing or pulling, altogether or none. ?
When it comes to choosing we always have limited option , and need to decide on something, then defend it, till you can , then give up and change mind. I guess that will be mine strategy.
I gave my interpretation on the first page - it's often called the Newtonian or reaction theory. The best defence is that it fits reality, as demonstrated in anything from aircraft to sails and wind tunnel tests.
Select to expand quoteMacroscien said..
Chris 249 said..
NASA shows your theory to be wrong here;
and here
and thanks God NASA is always right
That's a pretty silly way of looking at it. The Challenger disaster was a management fault, not a problem with NASA's knowledge of the theory of flight. The trained experts like those you deride had already warned of the issue with the O-rings and low-temperature launches, and a scientist famously demonstrated the problem in the inquiry.
In other words, those who think and work like real scientists and engineers got it right beforehand and afterwards - it's just that some smartarses failed to listen to them. That's pretty much what is happening here.
Secondly, NASA has taken people to the moon and space probes to the edge of the galaxy. You have done neither. Therefore they have incomparably more proven expertise in this field than you do.
Thirdly, showing one problem, or even a few problems, is about as accurate as showing Antoine Albeau (sp) or Bjorn falling off a few times and then saying that because they fall off, they are crap at windsurfing and you are better at it.
Select to expand quoteChris 249 said..
Let me ask you a question - do you seriously think ...
You may have this wrong ( again).
I am not here to explain anything, clarify,take sides. I don't present my opinion at that matter at any second.
I am all ears, listening you yours.
Even more. I am simply forbidden to express my personal view, because, it becomes instantly subject to personal attack ( regardless of merit behind) .
What is a bit unfair , you just punching neutral arbiter on the scene.
