Can Plane Take Off

brekk said:

Galiem honestly...



As a Physics major I would expect you to be used to ignoring friction.

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Of course I am, when it is appropriate. In this case, it has too much bearing on the movement of the plane.

Friction is also typically only ignored in the case of systems that are already completely understood. Since this one is being investigated, it has to be included. We don"t just throw out the elements of the universe that are inconvenient.

edit: I should also note that our preliminary model that shows that the plane should take flight depends on the friction between the wheels and the belt.

the lifting force is labeled as Bernouli"s Force, as a physics major I would have thought you might have heard of it.

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I never heard of it before this thread, but yeah... Sorry, I overlooked it while thinking about the forces involved.

The thrust force is the big arrow with "AIR" next to it behind the plane.

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Same as above.

Normal Force is that big arrow over the plane named "GRAVITY"

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Incorrect. The normal force is gravity"s reaction force. It should point upward, opposite gravity.

The weight of the conveyor belt has no value, or connection to this problem.

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The weight can be useful in deriving the equations for other forces, even if it is not really needed to describe the problem. Also, the weight is needed for the normal force, which is in turn needed for friction.

Stop thinking of this as a complex physics problem, just use your own common sense if you have any.

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I have purposely cast aside common sense. It has gotten me into trouble too many times.

I can appreciate your perspective, honestly. Physicists (and students busting their asses to become full-fledged physicists) don"t just go by intuition. We model, investigate, and consider all elements of the problem. We are incredibly anal, but this is why physics is a science, and not exclusively an art.

Hooby said:

...imagine the belt as a wheel rather than a flat surface.

Think if you have two wheels of the same size, set them up on axels to be touching eachother, and then mark the same respective spot on the wheels while motionless. If you turn them both the same speed in the opposite direction, the forces will cancel out in a sort of way, and will always end up having the marks stay the same relative position on the two seperate wheels.

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Of course the marks stay in the same relative position in this example, that"s because the wheels would not move at all in your example.

However, in the plane experiment, the "two" forces that spin the wheel both come from the ground, and act in the same direction.

Hooby said:

Keep in mind all of this "plane standing still" stuff is assuming ideal situations, when in the real world it is impossible to have the ideals of solving this problem come completely true.

So yes a plane probably would take off eventually, assuming the conveyor belt is wide enough to keep the plane from falling off. But that is because of human error, and that bastard friction.

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I think you"re really missing the point. The plane isn"t standing still, and this really has nothing to do with human error.

ANYWAYS, Galiem I"d like to present an idea to you that relates to this problem:

Suppose that the converyor belt is programmed so that it has the same speed as the plane has, both relative to the ground. So, if the plane is moving 250mph relative to the ground, so is the conveyor. Does the plane take off at 250mph, or 500mph?

Uber Uberest ~Rathe said:

NERDS

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You"re on an internet gaming messageboard, moron.

Relative to what? If the conveyor belt then 500mph. If the ground then 250mph.

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Relative to the ground. I agree that, relative to the ground, it will take off at 250mph, or very close to is.

PS: Relative to the conveyor, it would be taking off at 0mph.

Frawdo said:

Suppose that the converyor belt is programmed so that it has the same speed as the plane has, both relative to the ground. So, if the plane is moving 250mph relative to the ground, so is the conveyor. Does the plane take off at 250mph, or 500mph?

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If the conveyor belt were to suddenly stop, and if the plane were to roll off of it, then the plane"s speed would be 500 MPH, because the belt"s energy would be transfered to the plane.

Without that transfer, it would be 250 MPH, as in the case of a frictionless belt.

The plane wouldn"t take off with this speed because the belt is an added load, thus some of the plane"s work goes toward the belt (even though the belt is self powered).

With a self powered belt, there is the possibility of this not being the case, if it adjusts its angular velocity rapidly readily enough. This would require absolutely perfect conditions, and would not be a general case for any plane on a conveyor belt that matches its speed.

In that case, there would be no friction between the two, if our thoughts in class today are correct (along with a couple of my peers" hypothesis). In this case, the plane would behave exactly as y"all describe. It would take off as if the belt were not there at all.

This post leaves out a lot of detail, so I hope that it"s clear. I just don"t want to turn what is already a long post into a twenty page paper.

The conditions of the system as we are investigating it out here on my end are exactly as worded in the opening post, with no added constraints or qualifiers.

Ok, once again I don"t think you"re seeing the simple picture, but let me try an entirely different angle.

Let"s assume that you"re right, SOMEHOW the conveyor belt causes to the plane to remain, relative to the ground, motionless. That is what you"re contending, right?

How fast, then, is the conveyor belt moving, relative to the ground?

Frawdo said:

Ok, once again I don"t think you"re seeing the simple picture, but let me try an entirely different angle.

Let"s assume that you"re right, SOMEHOW the conveyor belt causes to the plane to remain, relative to the ground, motionless. That is what you"re contending, right?

How fast, then, is the conveyor belt moving, relative to the ground?

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The speed of a point on the conveyor belt is twice that of a point on the wheel.

Here is what I don"t understand:

Ok let"s say you have a treadmill (just for ease of picturing in your mind). You have a rollerblade on your hand, and you are holding it in place. This would represent the two speeds being equal, and the rollerblades remaining in place.

Now if someone were to start pushing the rollerblades, to represent the planes" engines" thrust, let"s say the acceleration of the rollerblades is 1m/s^2. Now if this is a perfect conveyor that matches the rollerblades" speed at all times, that would mean that the conveyor"s acceleration would be 1m/s^2 in the opposite direction. The rollerblades will remain in the same spot after the acceleration.

Maybe I"m missing something key here ... who knows?

so instead of making a new thread i"d though i"d ask to see if anyone here remember"s a video about 911, it was somthing about explaining the crash"s with the planes and shit, i think i remember a whole bunch of people saying the video was fake and shit, but yeah i"ve got a friend who"s hardcore into the concpiracies and all that shit and i wanted to show him that video.

Now if someone were to start pushing the rollerblades, to represent the planes" engines" thrust, let"s say the acceleration of the rollerblades is 1m/s^2. Now if this is a perfect conveyor that matches the rollerblades" speed at all times, that would mean that the conveyor"s acceleration would be 1m/s^2 in the opposite direction. The rollerblades will remain in the same spot after the acceleration.

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the rollerblade will not remain in the same spot when someone starts pushing it, it will go forward, and the wheels will spin that much faster to compensate

Potam:

One of my peer"s hypothesis meets that question well.

Let"s take the rollerblades on the treadmill, with the skate being accelerated, and with free motion of the treadmill, but with friction. The rollerblade would turn the treadmill with the same speed with which its wheels turn.

This is just like any of the belts in your car, or even the ball bearings in the wheels of the rollerblade. Thus, at this point, a point on the treadmill moves with the same speed as a point on the wheel.

Now, turn on the motor such that it supplies an additional velocity equal to that of the wheel. Now, a point on the treadmill moves with twice the speed as a point on the wheel.

This is why I answered the above question in that way, and I"m kinda surprised that Fawdo didn"t say anything else. Of course, I think that is what he was getting at, as per the hypothesis my peer explained to me.

In this case, since the wheel and treadmill are connected, the treadmill now accelerates the wheel so that the skate itself has twice the momentum that it did previously.

This, according to that hypothesis, causes the skate to fly off of the treadmill with exactly the velocity it started with, before the motor in the treadmill was turned on.

This makes sense, because the wheel would have an instantaneous reaction to the change in the treadmill before equilibrium could be established.

Remove friction, hold the wheel down with a large enough mass, or take away the wheel"s thrust, and it just sits there.

We"ll be setting up several experiments like what you describe to help us design the scaled down model of the plane problem.

Speaking of which... Does anyone know where to get a model plane that would be suitable for this experiment? It doesn"t necessarily have to be one of the big fancy ones that the serious model plane enthusiats use, but it shouldn"t just be a wind up toy either.

I haven"t slept in almost twenty four hours now, and my mind is working much more sluggishly than normal, so I should go rest. Have a good night, y"all.

Blaezenfury said:

so instead of making a new thread i"d though i"d ask to see if anyone here remember"s a video about 911, it was somthing about explaining the crash"s with the planes and shit, i think i remember a whole bunch of people saying the video was fake and shit, but yeah i"ve got a friend who"s hardcore into the concpiracies and all that shit and i wanted to show him that video.

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The Pentagon Thing Download

If I push a retard down the stairs, and the stairs escalade at the same rate as the retard falling down the stairs, would he ever hit the bottom? Take bouncing into account.

Discuss.

Frawdo said:

Let"s assume that you"re right, SOMEHOW the conveyor belt causes to the plane to remain, relative to the ground, motionless. That is what you"re contending, right?

How fast, then, is the conveyor belt moving, relative to the ground?

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You never really answered my question.

My point was that if we took your conclusion, assumed that it was right, then looked at the question backwards, we couldn"t really explain it. Erm, hmm.

I think the answer to my question above is that the conveyor belt, relative to the ground, is not moving at all. Remember, the conveyor belt matches the speed of the plane?

The plane starts at rest. And you"re telling me that, at some point in the future, the plane will still be motionless. Assuming a constant velocity, that means the plane has been moving at 0 m/s the entire time. And since the conyevor belt always matchs the speed of the plane, it"s been moving at 0 m/s the entire time too. But that doesn"t really make sense.

Therefore, your conclusion can"t be correct. The plane must move, relative to the ground and to the air.

Frawdo said:

You never really answered my question.

My point was that if we took your conclusion, assumed that it was right, then looked at the question backwards, we couldn"t really explain it. Erm, hmm.

I think the answer to my question above is that the conveyor belt, relative to the ground, is not moving at all. Remember, the conveyor belt matches the speed of the plane?

The plane starts at rest. And you"re telling me that, at some point in the future, the plane will still be motionless. Assuming a constant velocity, that means the plane has been moving at 0 m/s the entire time. And since the conyevor belt always matchs the speed of the plane, it"s been moving at 0 m/s the entire time too. But that doesn"t really make sense.

Therefore, your conclusion can"t be correct. The plane must move, relative to the ground and to the air.

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That arguement would be valid if you were talking about speed and not velocity. You can go around the world in 80 days but if you end up at the exact same spot your velocity will be 0. Velocity is speed over a distance, IE: If you are going at a constant speed of 100mph, head directly north for 30 minutes; then turn directly east for 30 minutes, your average velocity will be 71 mph NE not 100mph. (50^2 + 50^2 = c^2).

If you head out to pick up dinner and drive back to where you came from no matter how far you went your average velocity for the entire trip is 0, which should explain the 0m/s thing.

Did he say anywhere that the plane was in an atmosphere? If it"s in a vacuum, you"d get no lift except possibly from the equal/opposite force from any exhaust gases from the engine if they pointed down at all. Use an electrical engine (or a rubber band if it"s a really tiny plane!) = no exhaust = move the conveyor at any speed and the plane isn"t going up at all...

RdT.

OMFG. The plane WILL fly people. End of story. If you can"t read and comprehend why then maybe you need to take a basic physics class.

Shogon said:

You"re on an internet gaming messageboard, moron.

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That made me lol, good one (no sarcasm).