Will it take off?

[Jeff Matthews]

Dang, Ray! That was good! You really help to clear some of the old fog.

If the little fly didn't just bump the plane, but bumped it and kept flapping its wings, then, we would have a constant force and acceleration? Correct? Acceleration uninterrupted is ever-increasing speed, right? I ask genuinely because you brought back to the table all these old concepts and formulas that went dim to me long ago.

Oldie, yes, do call me when you're in Houston. I PM'd you my contact info.

[pauln]

Hey Jeff,

Ray's excellent answer is exactly like the one I would like to have provided.

And your additional extension about the little fly that keeps pushing is correct for non-relativistic speeds -so maybe there is hope for you yet.

Please don't think I'm so smart; I have yet to comprehend the concept of promissory estoppel since I ran across it over two years ago...

[PhilMays]

Hey Jeff,

Ray's excellent answer is exactly like the one I would like to have provided.

And your additional extension about the little fly that keeps pushing is correct for non-relativistic speeds -so maybe there is hope for you yet.

Please don't think I'm so smart; I have yet to comprehend the concept of promissory estoppel since I ran across it over two years ago...

Hell...I can't figure out a lawyers word "reasonable" []

[Ray Garrison]

Dang, Ray!  That was good!  You really help to clear some of the old fog. 

If the little fly didn't just bump the plane, but bumped it and kept flapping its wings, then, we would have a constant force and acceleration?  Correct?  Acceleration uninterrupted is ever-increasing speed, right?  I ask genuinely because you brought back to the table all these old concepts and formulas that went dim to me long ago.

Oldie, yes, do call me when you're in Houston.  I PM'd you my contact info. 

Your example of a fly bumping a plane is not only correct, but actually has a real-world counterpart, surprizingly enough.

Ever heard of a light sail?  Idea is if you have a spacecraft far enough out from the atmosphere that there's no drag to speak of, in other words your ideal frictionless environment, then any force applied to the spacecraft, however slight, will accelerate it.  Slowly, but constantly.  Okay, so build a big parachute-like sail.  Reflectorized mylar.  Deploy it in front of the spacecraft.  Photons, which are practically massless but moving really damn fast, will hit the sail, bounce off, and impart some portion of their kinetic energy to it.  This will accelerate the spacecraft away from the sun, toward intersteller space.  Away we go, slowly but surely.

Here's what the Jet Propulsion Lab at NASA has to say about it.

[oldtimer]

I knew sailing would eventually come into this.

[DizRotus]

Ray Garrison directed us to this link: Here's what the Jet Propulsion Lab at NASA has to say about it. The JPL link introduced sailing into this thread.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Sailinglike this whole threadis counter-intuitive. Most non-sailors are surprised to learn that a sailboat is "pulled" by the low pressure area in front of the sail on a broad reach, and that a sailboat goes faster on a broad reach than when going straight down wind.

The phenomenon is even more pronounced with iceboats. The ubiquitous DN iceboat can go 60 mph on a reach in a 20 mph wind; it seems like getting something for nothing, but its not. Thank the low friction of runners on ice, the vector forces and the Bernoulli Effect. Theres no perpetual motion and no free lunch. Speeding across the ice powered only by the wind is a real rush.

[Jeff Matthews]

Hey Jeff,

Ray's excellent answer is exactly like the one I would like to have provided.

And your additional extension about the little fly that keeps pushing is correct for non-relativistic speeds -so maybe there is hope for you yet.

Please don't think I'm so smart; I have yet to comprehend the concept of promissory estoppel since I ran across it over two years ago...

But Paul, the imprtant part is that you know the concept of promissory estoppel exists.

"The elements of promissory estoppel are a promise, foreseeability by the promisor that the promisee would rely on the promise, and substantial reliance by the promisee to his detriment. Allied Vista, Inc. v. Holt, 987 S.W.2d 138, 141 (Tex.App.-Houston [14th Dist.] 1999, pet denied)."

My calling you "quite-the-physicist" was purely in jest. I should have put one of those smiley's afterward.

[Jeff Matthews]

Hey Jeff,

Ray's excellent answer is exactly like the one I would like to have provided.

And your additional extension about the little fly that keeps pushing is correct for non-relativistic speeds -so maybe there is hope for you yet.

Please don't think I'm so smart; I have yet to comprehend the concept of promissory estoppel since I ran across it over two years ago...

Hell...I can't figure out a lawyers word "reasonable" []

Neither can I, and I'm a lawyer. If you ever figure it out, let me know, and we can make millions!

[bodcaw boy]

Do you really want to know Jeff? Yes, he's right about the literal ridiculousness of the statement, but I for one did not take you literally. Did I give you more credit than was due?

Yeah, Oldie, I really want to know. It may be a literally ridiculous statement, but I saw a similar statement while researching this jet issue. I recall when I took physics many years ago that there were alot of seemingly absurd nuances in physics that you don't think about - such as the ground pushes against a car.

I took the statement at face value with the idea being that if there is no friction to stop an object once it starts in motion, it will move forever. I know that is not exactly the statement made, so I'd like to know what happens in the example I posted. Somebody here who recalls all those formulas might certainly be able to show the math.

Relatavistic effects aside, it's pretty simple. An object's velocity is defined as a change in position over time. Changes in velocity result from acceleration. Specifically, an object's velocity at any time "T" is given by the sum of its initial velocity plus the rate of acceleration times the time during which it has been accelerating. That is, Vt = Vo + aT. An object with an initial velocity of 0 m/s accelerating at 10 m/s for 5 seconds will be traveling at 50 m/s at the end of that time. If the acceleration is removed at that point (we run out of gas) and we are in a frictionless environment (as you stated) the object will continue to move at 50 m/s indefinately.

The rate of acceleration is determined by the formula Force = Mass X Acceleration, or Force / Mass = Acceleration. If we apply a force of 1 Newton (one kilogram meter per second per second) to a 2 kilogram mass, it will begin to accelerate at a rate of 0.5 meters per second per second.

If relativity were not a factor, any acceleration applied continuously to a mass would continue to accelerate that mass without bound. Given a sufficient amount of time during which the acceleration was applied, the mass could attain any specific finite velocity. This is pretty much true for most things we interact with (planes, cars, guns, baseballs) because the velocities are so low compared to the velocity of light ©. The proportional amount of relativistic effects can be approximated by dividing something (mass, in this case) by the term (1 - (v^2 / c^2)) (that is, one minus (velocity squared divided by the speed of light squared)). At any speed far below the speed of light, the v^2 / c^2 term approaches zero, so the mass is divided by (1-0), or 1. As velocity begins to approach c, this term begins to take on a value that impacts the mass, increasing it. As velocity begins to approach c, mass begins to increase rapidly. This is important in things like partical accelerators, where the partical streams are moving at a significant portion of the velocity of light.

oh oh!! somebody owes jeff matthews an apology......[:$]

jeff,

hook em horns!!

roy delgado

[bodcaw boy]

Dang, Ray! That was good! You really help to clear some of the old fog.

If the little fly didn't just bump the plane, but bumped it and kept flapping its wings, then, we would have a constant force and acceleration? Correct? Acceleration uninterrupted is ever-increasing speed, right? I ask genuinely because you brought back to the table all these old concepts and formulas that went dim to me long ago.

Oldie, yes, do call me when you're in Houston. I PM'd you my contact info.

Your example of a fly bumping a plane is not only correct, but actually has a real-world counterpart, surprizingly enough.

Ever heard of a light sail? Idea is if you have a spacecraft far enough out from the atmosphere that there's no drag to speak of, in other words your ideal frictionless environment, then any force applied to the spacecraft, however slight, will accelerate it. Slowly, but constantly. Okay, so build a big parachute-like sail. Reflectorized mylar. Deploy it in front of the spacecraft. Photons, which are practically massless but moving really damn fast, will hit the sail, bounce off, and impart some portion of their kinetic energy to it. This will accelerate the spacecraft away from the sun, toward intersteller space. Away we go, slowly but surely.

Here's what the Jet Propulsion Lab at NASA has to say about it.

WOW! ray!! impressive!! but have you have seen a fly push a plane to jump start it? hmmmmm..

[sputnik]

What a drag that I missed this thread! ..................

You should consider yourself very fortunate - this thread is an entropy sink.[:|]

[Klipschguy]

I dunno, MDeneen, the original problem states that one must assume infinite friction leading to an infinite or perfect tether situation....just kidding.

[pauln]

Infinite friction... that sounds like part of what happens when an irresistable force meets an immovable object... "don't go there..."

How about a new thread titled "Will she take it off?"[]

[Jay481985]

wow taking a hiatus from this thread due to finals and moving but finally we are at agreement, sorry jeff I couldn't pick up when you called to tell you this sooner....

[Jeff Matthews]

wow taking a hiatus from this thread due to finals and moving but finally we are at agreement, sorry jeff I couldn't pick up when you called to tell you this sooner....

No problem. Hope your finals went well.

[Jay481985]

I hope so too [:$]

[D-MAN]

Hasn't anyone resolved this? The wing needs airspeed to create lift. So it is simply down to the speed of the air over the wing whether the plane in question flies or not.

The confusion seems to lie in whether you think either the plane is moving through the air, or the air is moving over a stationary wing. Either would cause lift if it results in enough air moving over the wing(s).

If you think that a jet engine SUCKS enough air to cause lift on a stationary wing, then you are wrong. The engine produces thrust which moves the airplane through the air, whether on the ground or in the air, it is the movement of air over the wing that causes lift. The velocity of air at the respective jet intake is far less than the accellerated and expanded air velocity (and volume) at the exhaust.

If the airplane was prevented from moving (as when the forward movement resulting from the thrust is counteracted by an equal force in the opposite direction) by a moving conveyor, the plane itself remains stationary, and that means no air speed over the wings. It doesn't matter that the wheels are free-wheeling, it is the motion of the plane THROUGH the static air that matters. And in the case that the conveyor is turning the wheels in an opposite direction at a speed to cancel the force of thrust, the plane remains stationary in position.

The fact that a conveyor running the opposite direction at equal speed to cancel the effects of available engine thrust would also prevent enough lift to get the airplane off the ground, as the amount of air moving over the entire airfoil would be insufficient to allow flight. Like I mentioned before, zero airspeed = zero lift.

You could, however, achieve flight from a stationary position in a wind-tunnel, providing you have generate enough wind. It all comes down to airspeed over the wings.

DM

[Champagne taste beer budget]

[:S]

[sputnik]

Hasn't anyone resolved this? The wing needs airspeed to create lift. So it is simply down to the speed of the air over the wing whether the plane in question flies or not.

The confusion seems to lie in whether you think either the plane is moving through the air, or the air is moving over a stationary wing. Either would cause lift if it results in enough air moving over the wing(s).

If you think that a jet engine SUCKS enough air to cause lift on a stationary wing, then you are wrong. The engine produces thrust which moves the airplane through the air, whether on the ground or in the air, it is the movement of air over the wing that causes lift. The velocity of air at the respective jet intake is far less than the accellerated and expanded air velocity (and volume) at the exhaust.

If the airplane was prevented from moving (as when the forward movement resulting from the thrust is counteracted by an equal force in the opposite direction) by a moving conveyor, the plane itself remains stationary, and that means no air speed over the wings. It doesn't matter that the wheels are free-wheeling, it is the motion of the plane THROUGH the static air that matters. And in the case that the conveyor is turning the wheels in an opposite direction at a speed to cancel the force of thrust, the plane remains stationary in position.

The fact that a conveyor running the opposite direction at equal speed to cancel the effects of available engine thrust would also prevent enough lift to get the airplane off the ground, as the amount of air moving over the entire airfoil would be insufficient to allow flight. Like I mentioned before, zero airspeed = zero lift.

You could, however, achieve flight from a stationary position in a wind-tunnel, providing you have generate enough wind. It all comes down to airspeed over the wings.

DM

[8-)] You really should take some time and read through the thread.

[pauln]

D-Man, it does not matter what is going on with the wheels or the conveyer - the wheels are free rolling. The conveyer may change the rate of rotation of the wheels, but that means nothing to the plane. The thrust will push the plane forward and air will flow over and under the wings... no matter what the conveyer and wheels do - it takes off and flies.