Can Plane Take Off
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Tuco
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Since I"m 0/1 in this thread, I answer meekly.
Assuming the plane is going mach 1 in relation to you, and is not traveling directly toward you, wouldn"t it not give you a sonic boom until it passed you?
(I don"t know how sonic booms work, I just figured it was the continual build up of sound that stays near the front of the plane because the plane is going the same speed as sound).
brekk
Dancing Dino Superstar
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Lenardo has it right.
The two systems in the question are:
#1 Airplane Wheels + Conveyor Belt
#2 Jet Engine Thrust + Air
These two systems are completely seperate. System #1 can be completely ignored as it has no impact on the aircrafts motion.
If you look solely at system #2 the plane will take-off.
The two systems in the question are:
#1 Airplane Wheels + Conveyor Belt
#2 Jet Engine Thrust + Air
These two systems are completely seperate. System #1 can be completely ignored as it has no impact on the aircrafts motion.
If you look solely at system #2 the plane will take-off.
Eomer
Trakanon Raider
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Hell yes. If it"s flying really low and more or less in a direct line towards you, the sonic boom would arrive at virtually the same time as the plane. Technically it would be slightly after, but it"d be tough to distinguish and afterwards you"d be more concerned with changing your underpants.
The answer is yes, if you ignore all the complications that could arise with having a commercial jet liner on a large conveyor belt (or whatever size plane you had in mind). The conveyor belt would not apply any significant force against the airplane, hence the airplane"s engine"s would accelerate the plane as it would on a regular runway, the wings would start to get lift from the air movement, and once it reached a high enough speed it"d take off.
Everyone"s distracted by the conveyor belt somehow magically holding the plane still. It doesn"t, and therefore the plane will fly as normal.
Camerous
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You can replace the damn wheels with hover jets if you want to...it doesn"t matter. The forward movement, which is what creates the lift for the plane, doesn"t come from the wheels. It comes from the engines. The wheels serve no other purpose in taking off but pointing the plane in the right direction and to keep the under belly of the plane from scraping the ground.
As for the sonic boom, yes you would hear it...is this even a real question? Why would you not hear it?
Pretty plain and simple I thought.
As for the sonic boom, yes you would hear it...is this even a real question? Why would you not hear it?
Pretty plain and simple I thought.
Eomer
Trakanon Raider
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Well, like I said the original question was very poorly worded and it"s easy to see why some people couldn"t figure it out.
That makes it sound like the plane is stationary. I read it a couple times before I could figure out what the fuck they were even asking. It"s more of an exercise in reading comprehension than anything.
Ah, that"s the piece I was missing, everyone seemed to be off their fucking rocker there who was in favor of the plane taking off. So it is moving forward relative to the ground and air (YES it is required the plane move forward relative to the air to fly, this is absolutely necessary, and this requires it to move forward relative to the ground -- not the belt -- unless you have some wicked and perfect wind going on), since the force is being applied to the air to make the plane move forward and not the ground, the belt speed is a non-factor as the plane must move forward through the air to be moving forward at all. Got it.Brodda Thep said:
Its all about the windspeed relative to the plane. If there is no wind, a plane needs to move foreward through space to achieve sufficient lift to take off. If there were a 200mph headwind, the plane could take off with no engines at all (barring death and destruction). You can go out on a windy day and see birds glide backwards.
This is true in that if you hold a plane in place until its thrust is at a maximum, it will achieve the required takeoff speed much more quickly once the break is released. However, if you were to tether a plane in place with no wind speed, it would just sit there pulling on the tether. It would not take off since there would be no windspeed and thus no lift would be created.
Yes, the air returns this force via thrust. Using the tether example, the plane then delivers this force to the earth via the tether, which exerts and equal force onto the plane keeping it from moving. The air pusing on the plane is trying to move it, the the tether is pulling on the plane keeping it from moving. Airspeed and lift are not involved.
Ok, using a shopping cart as an example... The cart would be on a conveyer, and I"m pusing it. The key point here is that I"m not on the conveyer. I"m standing beside the conveyer exerting a force on the cart (the stationary ground beside the conveyer is independent from the conveyer just as the air above the conveyer is in the plane example). Assuming no friction, the conveyer can move infinitly fast, and I can hold the cart still, move it backward or foreward at any speed I want. There is no way whatsoever that the conveyer can keep me from moving the cart, and there is no way that a conveyer could keep a plane from moving foreward.
OK, I think I see where I made my mistake earlier.
I was placing the movement of the plane in reference to the conveyor. The plane doesn"t get its forward thrust due to friction with the conveyor however.
Instead, the movement should be in reference to the *air*. The propellor will pull the plane through the air at 100 mph regardless of how fast the wheels below may be spinning.
What finally made me say "AH HA!" was this:
I was placing the movement of the plane in reference to the conveyor. The plane doesn"t get its forward thrust due to friction with the conveyor however.
Instead, the movement should be in reference to the *air*. The propellor will pull the plane through the air at 100 mph regardless of how fast the wheels below may be spinning.
What finally made me say "AH HA!" was this:
So, uhm ... is it too late to change my vote?
i found this dilemma very useful in explaining to my friend why it doesn"t help to spin the tires of his car constantly when he"s stuck in the snow and there are 2 guys behind him trying to push the car out.
Why still all this nonsense about the wheels exerting no force because they are rolling?
I brough this up in physics today, and we spent an hour discussing it with a PhD in theoretical physics who has "over 40 years" (his words) experience as a physicist. Also, he is a Nobel Leuraete. I trust our preliminary conclusions.
Augment him with a dozen physics students, and you have a rapid action think tank for this kind of problem. I even have the preliminary free body diagrams now.
First of all, the wheels DO transfer force to the conveyor belt. The force does not originate in the wheels, but it IS transfered to the belt as part of the chain of forces that result from the jet.
Now, here are the things that we are certain of:
1) The conveyor belt is not a momentum resevoir. I should have noticed this last night. There is zero momentum on the conveyor belt at all times because equal momentum exists on it on two sides that is opposite in direction.
2) As a result of the above fact, something has to move. The conveyor belt"s motion is not the only motion happening. This leads to only a handful of distinct possibilities.
3) If the brakes are applied and held, the plane will take flight.
4) If the brakes are not applied, the plane will oscillate in the very least. It will take small "jumps" in this case, until it falls off the end of the conveyor belt. This possibility is likely the real reason that Myth Busters won"t touch this. If this were to occur, then they would destroy a working jet. That is a very expensive proposition.
5) Friction can NOT be ignored. The conveyor belt is not ideal, but its inner workings are. If friction is ignored, then the plane never moves a millimeter forward or up. Not to mention that, without friction, the conveyor belt might as well not even be there.
6) Friction becomes zero if and when the plane reaches liftoff velocity relative to the ground. This results in the plane"s lifting off.
7) We are not certain whether we can determine for certain whether absolutely any given plane will lift off in this scenario.
8) Any skid in the wheels (like a car "spinning out") will inevitably lead to the plane"s lifting off. Such skid is highly likely to occur.
9) The conveyor belt will have an extremely dangerously high ammount of inertia transfered to it as the plane takes flight (IF the plane does take flight). If this stunt were ever performed, and anyone were to accidentally brush the belt even the slightest, that person would be torn to pieces almost instantly.
We will be continuing our work tomorrow. Once class lets out, I"m going to take all of the free body diagrams and equations to a scanner, and I will post them along with our final solution.
Speculation with pseudo science is one thing, but we"re giving y"all the real thing.
Also --- and I know that y"all will love this --- we"re working on ways to set up a scaled down model of this experiment for you. To hell with waiting on Myth Busters! It may take us some time, but we should have a video ready for you by the end of next semester, so you"ll be able to see for yourself what happens.
I brough this up in physics today, and we spent an hour discussing it with a PhD in theoretical physics who has "over 40 years" (his words) experience as a physicist. Also, he is a Nobel Leuraete. I trust our preliminary conclusions.
Augment him with a dozen physics students, and you have a rapid action think tank for this kind of problem. I even have the preliminary free body diagrams now.
First of all, the wheels DO transfer force to the conveyor belt. The force does not originate in the wheels, but it IS transfered to the belt as part of the chain of forces that result from the jet.
Now, here are the things that we are certain of:
1) The conveyor belt is not a momentum resevoir. I should have noticed this last night. There is zero momentum on the conveyor belt at all times because equal momentum exists on it on two sides that is opposite in direction.
2) As a result of the above fact, something has to move. The conveyor belt"s motion is not the only motion happening. This leads to only a handful of distinct possibilities.
3) If the brakes are applied and held, the plane will take flight.
4) If the brakes are not applied, the plane will oscillate in the very least. It will take small "jumps" in this case, until it falls off the end of the conveyor belt. This possibility is likely the real reason that Myth Busters won"t touch this. If this were to occur, then they would destroy a working jet. That is a very expensive proposition.
5) Friction can NOT be ignored. The conveyor belt is not ideal, but its inner workings are. If friction is ignored, then the plane never moves a millimeter forward or up. Not to mention that, without friction, the conveyor belt might as well not even be there.
6) Friction becomes zero if and when the plane reaches liftoff velocity relative to the ground. This results in the plane"s lifting off.
7) We are not certain whether we can determine for certain whether absolutely any given plane will lift off in this scenario.
8) Any skid in the wheels (like a car "spinning out") will inevitably lead to the plane"s lifting off. Such skid is highly likely to occur.
9) The conveyor belt will have an extremely dangerously high ammount of inertia transfered to it as the plane takes flight (IF the plane does take flight). If this stunt were ever performed, and anyone were to accidentally brush the belt even the slightest, that person would be torn to pieces almost instantly.
We will be continuing our work tomorrow. Once class lets out, I"m going to take all of the free body diagrams and equations to a scanner, and I will post them along with our final solution.
Speculation with pseudo science is one thing, but we"re giving y"all the real thing.
Also --- and I know that y"all will love this --- we"re working on ways to set up a scaled down model of this experiment for you. To hell with waiting on Myth Busters! It may take us some time, but we should have a video ready for you by the end of next semester, so you"ll be able to see for yourself what happens.
I"m really surprised that a Physics major isn"t able to grasp this concept yet. I think the fact that you"re into advanced physics has caused you to make this problem more complex than it is, Galiem.
Anyone should be able to use common sense to figure this out eventually. First year physics students should find this problem blatantly obvious.
The plane will fly. It doesn"t matter what speed the converyor moves at, it is not going to effect the horizontal movement of the plane (not true, actually, but the effect will be so small and neglible that for the purpose of the experiment we can consider it to be equal to 0).
Anyways, you should research it and do a proper force diagram to prove us right. A normal plane won"t ever lift off vertically either. The upwards force requires the horizontal movement. Even if you had a motionless plane and enough wind blowing at it to get it off the ground, it wouldn"t go straight up.
Anyone should be able to use common sense to figure this out eventually. First year physics students should find this problem blatantly obvious.
The plane will fly. It doesn"t matter what speed the converyor moves at, it is not going to effect the horizontal movement of the plane (not true, actually, but the effect will be so small and neglible that for the purpose of the experiment we can consider it to be equal to 0).
Anyways, you should research it and do a proper force diagram to prove us right. A normal plane won"t ever lift off vertically either. The upwards force requires the horizontal movement. Even if you had a motionless plane and enough wind blowing at it to get it off the ground, it wouldn"t go straight up.
That might be the case, but the evidence y"all offer is partly erroneous, and partly requires faith.Frawdo said:
I should not longer say that y"all are completely wrong. I"m not entire certain either way at this point.
Your free body diagram is missing some key forces:
Friction between the wheels and the belt
Friction between the belt and any non-internal things it touches (air if nothing else)
The normal force on the plane, and on the conveyor belt
The lifting force (important one!)
The thrust force (also important!)
The weight of the conveyor belt
These things do play a big role in it.
If it turns out that y"all are right, then I"ll just be giving you a lot of fancy ways to explain it to other folks and impress them
P.S. The real proof of this is complex enough that the entire physics staff has been debating it all day.
OH! How could I forget?
The origin of this problem is a Russian "Fair of Intellect".
edit: I"ll be giving y"all a couple preliminary force diagrams tomorrow I should have a final one ready by this weekend
People keep assuming that the belt moving backwards means it will speed up the wheel... that won"t happen if it matches the wheels speed exactly, it"s easier to think about it if you 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.
The wheels are both still exerting force on eachother, but neither one will ever gain any advantage over the other. The same will stand true for a wheel on a flat moving surface, as the surface area of a wheel touching a flat surface is equivilant to the surface area of a wheel touching flat ground.
Regarding the shopping cart example, that is the reason the plane will probably end up "bouncing" but not gaining much if any horizontal movement.
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.
On a side note, the construction on the street outside my house has turned my computer chair into a giant vibrator.
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.
The wheels are both still exerting force on eachother, but neither one will ever gain any advantage over the other. The same will stand true for a wheel on a flat moving surface, as the surface area of a wheel touching a flat surface is equivilant to the surface area of a wheel touching flat ground.
Regarding the shopping cart example, that is the reason the plane will probably end up "bouncing" but not gaining much if any horizontal movement.
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.
On a side note, the construction on the street outside my house has turned my computer chair into a giant vibrator.
Uber Uberest
rdr^2
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brekk
Dancing Dino Superstar
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Galiem honestly...
the lifting force is labeled as Bernouli"s Force, as a physics major I would have thought you might have heard of it.
The thrust force is the big arrow with "AIR" next to it behind the plane.
Normal Force is that big arrow over the plane named "GRAVITY"
The weight of the conveyor belt has no value, or connection to this problem.
Stop thinking of this as a complex physics problem, just use your own common sense if you have any.
as for your idea above:
Boeing 757; 58513.63636kg 2x engines producing 380,000 total newtons of thrust
now lets use the most basic of physics equations.
F=MA
F(380kN) = M (58513.63636kg) * A
And you get an acceleration of 6.5 m/s*s
This is first semester of freshmen year physics... Hell this is highschool physics. And guess what!? In those basic level physics classes friction is always ignored.
As a Physics major I would expect you to be used to ignoring friction.
the lifting force is labeled as Bernouli"s Force, as a physics major I would have thought you might have heard of it.
The thrust force is the big arrow with "AIR" next to it behind the plane.
Normal Force is that big arrow over the plane named "GRAVITY"
The weight of the conveyor belt has no value, or connection to this problem.
Stop thinking of this as a complex physics problem, just use your own common sense if you have any.
as for your idea above:
Here"s a few calculations:
Boeing 757; 58513.63636kg 2x engines producing 380,000 total newtons of thrust
now lets use the most basic of physics equations.
F=MA
F(380kN) = M (58513.63636kg) * A
And you get an acceleration of 6.5 m/s*s
This is first semester of freshmen year physics... Hell this is highschool physics. And guess what!? In those basic level physics classes friction is always ignored.