RichR
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I'm talkign more about the connectivity and friction between the tyres (contact patch) and the ground plane - the mass is exerted over a given area and this is where velocity of advance is found
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Steve
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push or pull where is the difference? if you were stood behind it with a stick pushing it the same applies.
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Steve
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we have given several real life examples of why it would, what can you give apart from theorys? your examples about the treadmill that rotates as fast as you are running does not work either as the legs (wheels) are doing the propulsion in that example
[Edited on 24-05-2006 by Steve]
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Cosmo
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quote:
Originally posted by Cosmo
the big question is.....
If this was a plane, the engines would either run out of power and not be strong enough to overcome the friction between the wheels and conveyor so not move anywhere...or if they are strong enough they would push the plane forward but if thats at a speed to take off I dont know.
I dont know the maths, or the figues for the engines, weight of plane, lift, etc. to work that out and wouldnt want to guess!
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Steve
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yes there is a small amount of frictional force pushing the plane backwards, but this is very small compared to the force being applied by the jets
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RichR
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quote:
Originally posted by Steve
we have given several real life examples of why it would, what can you give apart from theorys? your examples about the treadmill that rotates as fast as you are running does not work either as the legs (wheels) are doing the propulsion in that example
[Edited on 24-05-2006 by Steve]
no the legs are the engine - the feet are the wheels through which the velocity of advance is placed
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Cosmo
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quote:
Originally posted by Steve
yes there is a small amount of frictional force pushing the plane backwards, but this is very small compared to the force being applied by the jets
have you done the maths for this or just guessing?
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Steve
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quote:
Originally posted by LiVe LeE
quote:
Originally posted by Steve
we have given several real life examples of why it would, what can you give apart from theorys? your examples about the treadmill that rotates as fast as you are running does not work either as the legs (wheels) are doing the propulsion in that example
[Edited on 24-05-2006 by Steve]
no the legs are the engine - the feet are the wheels through which the velocity of advance is placed
no because the feet arent freewheeling, they are fixed to the force being apllied by the legs, if you had a jet pack on your back pushing you forwards your legs running, no matter how fast would have no effect on the force being applied by the jetpack
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SVM 286
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quote:
Originally posted by Steve
he will still be able to pull you off the end of the treadmill.
Cheeky 
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RichR
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frictional force wont be as small as your assuming - the frictional force is a result of mass*gravity*contact area
and also
Friction is a function of 1/2*p*S*V^2*Cd
where Cd is the Coefficient of Drag
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RichR
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quote:
Originally posted by Steve
quote:
Originally posted by LiVe LeE
quote:
Originally posted by Steve
we have given several real life examples of why it would, what can you give apart from theorys? your examples about the treadmill that rotates as fast as you are running does not work either as the legs (wheels) are doing the propulsion in that example
[Edited on 24-05-2006 by Steve]
no the legs are the engine - the feet are the wheels through which the velocity of advance is placed
no because the feet arent freewheeling, they are fixed to the force being apllied by the legs, if you had a jet pack on your back pushing you forwards your legs running, no matter how fast would have no effect on the force being applied by the jetpack
it would if you stood completely still - didnt move your feet and the rocket pack propeeled you perfectly horizontally - the treadmill would increase in speed to keep you in the same place
theoretically - would be hard to achieve the correct conditions for equilibrium
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Cosmo
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well until someone does the maths with all the correct figures its pointless debating it as it really could go one way or the other.
And BTW....I notice none of these answer posted (the external links) went into all the maths about it all.
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Steve
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its not really a question about maths, more about logic,
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RichR
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in fairness to the topic - we could debate all night - but theres a possibility that this is turning into one of the most interlectual debates CS has ever seen 
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3CorsaMeal
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6 sausages under a tissue box, 6 more sausages under those
blow the tissue box from behind
do you feel like a complete idiot and wonder when you gonna eat 12 sausages now you've opened them?
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RichR
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yes and your thinking that friction is easy to overcome - its not that easy! - especially with a counteracting conveyor
[Edited on 24-05-2006 by LiVe LeE]
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Jules S
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quote:
Originally posted by LiVe LeE
if all four wheels of the quad were in rollers; you could push the quad side to side, easily but you couldnt push it backwards or forwards, the quad would be suspended in its static equilibrium - as you pushed the velocity of advance would increase and the rollers would increase to counteract the increase in speed - the quad would go nowhere but the wheels would simply rotate faster, as would the rollers
If I chose to push the quad forwars or backwards I could with ease. the forces are directed through my body onto the surrounding concrete, not the rollers.
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Steve
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quote:
Originally posted by LiVe LeE
yes and your thinking that friction is easy to overcome - its not that easy! - especially with a counteracting conveyor
[Edited on 24-05-2006 by LiVe LeE]
it is easy to overcome when the wheel have things like bearings that make them spin easily
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Cosmo
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quote:
Originally posted by Steve
its not really a question about maths, more about logic,
depends if you want the real answer or not. Because theoretically it could take off...but it may need such huge jets that it would never happen.
The real answer would only ever be found out if someone can do the maths and find out if the planes jets provide enough force to counter the friction between the wheels and conveyor. And if they do, is it enough force to get upto a safe speed to take off.
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RichR
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not if you were stood on the conveyor
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Steve
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heres the proof
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3CorsaMeal
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quote:
Originally posted by Steve
heres the proof
spot on steve 
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Steve
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The Solution:
Here are the keys to understanding this problem:
The wheels of an aircraft are "free-wheeling". They do not provide propulsion, and therefore do not "push against" the action of the conveyor belt.
The thrust for aircraft movement comes from jet engines or propellors... not the wheels. Therefore, the thrust being applied to the aircraft body is completely decoupled from how fast the wheels happen to be spinning.
Thrust acts according to Newtons Third Law of Motion - every action has an equal and opposite reaction. The thrust of the engines is acting against the air.
Because the wheels are free-wheeling and we have assumed zero friction at the hub, it follows that the conveyor belt, no matter how fast it is moving, CANNOT EXERT ANY FORCE on the aircraft with respect to forward motion! There is no force in our experiment that can oppose the thrust vector of the aircraft.
If the conveyor belt cannot exert any relevant force on the aircraft, you can completely ignore it. Ergo, the aircraft takes off as if nothing unusual is happening.
Addressing Some Common Arguments:
1) "The conveyor belt will cancel out any forward motion of the aircraft. The plane will not move at all."
Short Answer: The belt has no way to exert force with respect to the forward motion of the aircraft. All it can do is make the wheels spin faster or slower.
Long Answer: Your conditions are illogical.
You claim that the aircraft will not move
If the plane doesn't move, then the conveyor belt doesn't move either
If the belt is not moving, then how is it cancelling any forward motion of the aircraft?
2) "The plane will remain stationary, but will lift into the air... thus taking off."
Answer: This is an aerodynamic impossibility (assuming no wind), which should be obvious.
3) "But if you said the the conveyor belt matches the speed of the WHEELS, it wouldn't be able to take off."
Short Answer: See Argument #1.
Long Answer: Once again, your conditions are illogical. The conveyor belt can never "match" the speed of the wheels unless the aircraft does not move. With a tremendous thrust vector behind it with no opposing force, the aircraft will move. Once the aircraft begins to move, we enter into a paradoxical situation.
X = Wheel Rotational Speed
X = Conveyor Belt Speed, as per your conditions
Z = Speed of Aircraft = Some non-zero positive number
The equation is: X = X + Z, which is illogical.
Example. The aircraft is moving 10mph (X = X + 10) with the wheels rotating at 10mph. Therefore, the belt must react and accelerate to 10mph. But now the wheels are rotating at 20mph... and so on to infinity.
4) "You can't just ignore the conveyor belt as you claim. Take this situation for example..."
A guy is standing on the conveyor. He sees a plane moving forwards away from him at 10mph on the conveyor. He also knows that the conveyor itself is also moving at 10mph in a forwards direction. The total velocity of the plane in relation to the ground must be 20mph.
If the conveyor can be ignored then why is the plane's total velocity twice what it would normally be if it was moving along on tarmac.
The fact that you cannot explain this indicates that you've either ignored or overlooked some of the forces at play between the conveyor and the plane.
I don't see any violations.
You state that the aircraft is moving 10mph relative to the conveyor (perhaps as measured by a speedometer on the wheels). The conveyor itself is moving 10mph relative to the ground in the same direction. The total speed of the aircraft relative to the ground (tarmac) is 20mph.
I don't see any problem with this. Ignore the conveyor by making it pop out of existence and you suddenly have an aircraft traveling down the tarmac at 20mph.
You can change your point of view as much as you like, but you still end up with an aircraft traveling 20mph with respect to the ground.
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SVM 286
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quote:
Originally posted by Steve
I need everyone to concentrate on this, then surely you must get it.
You are holding a 2 meter piece of string, the car is rolling on the spot on the treadmill, everytime you pull the string the car moves towards you by say for arguments sake 2 foot, even if the treadmill sped up to match the acceleration of the car, the string is fixed to the car and is shortenening in length each time, the car would have to move towards you, else you would be pulling on a piece of string that never ended
as for going on weight LIVELEE the theory is the same, if you were strong enough to pull a normal size car on a big conveyor belt using a piece of string the same would happen
[Edited on 24-05-2006 by Steve]
Yes, but Steve, the principle at hand is that this is not a toy car on a piece of string.
It is a full sized aircraft on a powered conveyor belt that MATCHES the craft's speed in reverse.
The fact that the belt moves as fast as the plane can, but in the opposite direction negates any possibilty of physical advance in relation to the craft's position on the ground.
There is no giant mythical hand and piece of string to assist the plane's progress.
All it has is it's own powered speed potential, and as the belt MATCHES the crafts speed in the opposite direction, the plane CANNOT take off.
If the plane could exceed the speed of the belt, and leave the end of it to get back onto tarmac it could easily take off of course, but it can't exceed the speed of the belt so it CANNOT take off.
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Jules S
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Registered: 24th Dec 03
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quote:
Originally posted by Cosmo
quote:
Originally posted by Steve
its not really a question about maths, more about logic,
depends if you want the real answer or not. Because theoretically it could take off...but it may need such huge jets that it would never happen.
The real answer would only ever be found out if someone can do the maths and find out if the planes jets provide enough force to counter the friction between the wheels and conveyor. And if they do, is it enough force to get upto a safe speed to take off.
Have you never seen that strong man chap who pulls 747's using ropes?
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