Airplane and conveyor belt thread...
Discussion
ATG said:No, I am not. I am saying they are freely allowed to accelerate and spin up to whatever equilibrium speed they need to get to. The wheels might apply a very, very slight braking force due to friction, but that is negligible.
Indeed, it is not about the wheels braking the aircraft in some manner to prevent it from taking off.
I'm afraid it is. In the thought experiment this is the only mechanism that is generating a force on the aircraft that opposes the thrust of the engines. I agree with you entirely about the wording of the question, but I think you're a attributing some magic powers to wheels that they don't posess.
The plane is not held in place due to braking. Rather, the acceleration thrust provided by the engines is transferred down to the wheels, and dissipated completely in the massive "spinning up" of the wheels to very high speeds. Typically this results in a forward roll. However, it's sitting on a belt moving in the opposite direction, matching the wheel speed at all times. So, they accelerate to massive speeds, but rotate in place. The plane ends up sitting still.
This image shows a motorcycle and sidecar, set up on half-road / half-conveyor belt...
At the moment the belt is spinning and the wheels are turning....
The bike engine is ticking over, but there is no forward motion.
Orgasmicliving....?
What will happen if the rider tries to pull away ?
At the moment the belt is spinning and the wheels are turning....
The bike engine is ticking over, but there is no forward motion.
Orgasmicliving....?
What will happen if the rider tries to pull away ?
r5gttgaz said:
But as the plane is not moving anywhere there would be no airflow over the wings and then no lift?
But it is moving forward, as the engines produce thrust backwards in the air pushing the plane forward resulting in lift being produced as airflows over the wing.
The only time the conveyor would have an effect is on landing when the plane brakes and attempts to stop, the only time during the whole flight, take off-landing that the wheels do anything other than support the planes weight to stop it sitting on the deck.
orgasmicliving!! said:I have done sooooo many times... I'll remind you about this when it sinks in
Have I missed a handbag session??
orgasmicliving said:
It really, really bugs me when people insist that their junk science is correct.
Do you annoy yourself often??
The subject came up in a different thread, and I didn't want to derail that one. Apparently this has been discussed here before?
Bliarout, instead of just insisting on your (incorrect) viewpoint, why don't you back it up with science/evidence/experimentation?
The correct physics has been explained so many times now that there is no point doing it again.
The plane takes off.
The wording of the question is rubbish. What exactly does the conveyor belt do? It goes at the same speed as the plane? Speed realtive to what? If the plane is staying still than so is the conveyor belt, so what is stopping the plane going forwards? It's totally meaningless gibberish.
The plane takes off.
The wording of the question is rubbish. What exactly does the conveyor belt do? It goes at the same speed as the plane? Speed realtive to what? If the plane is staying still than so is the conveyor belt, so what is stopping the plane going forwards? It's totally meaningless gibberish.
madazrx7 said:Afraid you are the one who has the relative motion slightly mixed up. Relative to the surface of the belt, whizzing along backwards, the tyres of the plane are screaming forward at very high speed (they have matching speeds, but in the opposite direction). Relative to the air, the plane is sitting still. Just like you being on a treadmill. You could spring along merrily, relative to the treadmill, but relative to the rest of the room, you are not moving forward.
OL, Just for a moment I will assume that you aren't taking the piss.
You seem to be confused in terms of relativity? If the 'conveyor belt' runway matched the speed of the wheels, then you are right, the plane would not be moving... RELATIVE TO THE CONVEYOR BELT. It would still be moving relative to the air, and everything else. Therefore, it would take off.
orgasmicliving!! said:
OL, Just for a moment I will assume that you aren't taking the piss.
You seem to be confused in terms of relativity? If the 'conveyor belt' runway matched the speed of the wheels, then you are right, the plane would not be moving... RELATIVE TO THE CONVEYOR BELT. It would still be moving relative to the air, and everything else. Therefore, it would take off.
Yes but your missing the point, imagine running on a treadmill in the gym, then turning on a jet pack on your back... what your saying is... If you ran fast enough you would stay still....
OK, imagine a supermarket checkout conveyor with a toy plane sitting in it. The plane is facing in the oposite direction to the direction of movement of the conveyor.
If left to it's own devices it would move backwards toward where you fill your bags. If a person reaches out and holds it in position then that person (the engine in this case, who is external to the conveyor) is counteracting the effects of the conveyor. As this point the wheel speed and conveyor speed are inherently the same (ok there will be some slip but you get the picture). Now said person applies additional force to move the plane forward, the conveyor speeding up to try and counter this forward motion, however it can't and the plane gets moved off the end of the conveyor and down the pet food aisle.
The only case in which this would not happen is if the engine could not supply enough thrust to overcome the friction of the tyres and bearings.
If left to it's own devices it would move backwards toward where you fill your bags. If a person reaches out and holds it in position then that person (the engine in this case, who is external to the conveyor) is counteracting the effects of the conveyor. As this point the wheel speed and conveyor speed are inherently the same (ok there will be some slip but you get the picture). Now said person applies additional force to move the plane forward, the conveyor speeding up to try and counter this forward motion, however it can't and the plane gets moved off the end of the conveyor and down the pet food aisle.
The only case in which this would not happen is if the engine could not supply enough thrust to overcome the friction of the tyres and bearings.
orgasmicliving!! said:Ahem, planes push against the air to get their motive power, the wheels just stop them sitting on their fuselage. The only force through the wheels is vertical, not fore and aft.
Indeed, it is not about the wheels braking the aircraft in some manner to prevent it from taking off.
I'm afraid it is. In the thought experiment this is the only mechanism that is generating a force on the aircraft that opposes the thrust of the engines. I agree with you entirely about the wording of the question, but I think you're a attributing some magic powers to wheels that they don't posess.
The plane is not held in place due to braking. Rather, the acceleration thrust provided by the engines is transferred down to the wheels, and dissipated completely in the massive "spinning up" of the wheels to very high speeds. Typically this results in a forward roll. However, it's sitting on a belt moving in the opposite direction, matching the wheel speed at all times. So, they accelerate to massive speeds, but rotate in place. The plane ends up sitting still.
blueyes said:
I thought to take off the plane would need air flowing over the wings to give it lift.
If it doesn't move- mega conveyor belt cancels out forward movement from engines- how will it take off.
Blueyes
2 O levels- geog and english.
Degree in ice cream making.
It is moving forward. The conveyor belt cannot stop the plane moving forward.
blueyes said:
I thought to take off the plane would need air flowing over the wings to give it lift.
If it doesn't move- mega conveyor belt cancels out forward movement from engines- how will it take off.
Blueyes
2 O levels- geog and english.
Degree in ice cream making.
It is moving forward. The conveyor belt cannot stop the plane moving forward.
DieselJohn said:
The correct physics has been explained so many times now that there is no point doing it again.
The plane takes off.
The wording of the question is rubbish. What exactly does the conveyor belt do? It goes at the same speed as the plane? Speed realtive to what? If the plane is staying still than so is the conveyor belt, so what is stopping the plane going forwards? It's totally meaningless gibberish.
Actually, incorrect physics has been applied. You are wrong, I am afraid. Are you saying you can't run in place on a treadmill? Of course you can. So, too, can a plane sit on a conveyor belt, tyres spinning, conveyor spinning in the opposite direction at the same speed, and the body of the plane not moving. What is stopping the plane moving forwards is the fact that no net force is being applied to push it forwards. Any force from the engines' thrust is going to accelerate the wheels, which spin faster and faster. But so does the conveyor, always exactly matching the tyre speeds in the opposite direction.
orgasmicliving said:
the tyres of the plane are screaming forward at very high speed (they have matching speeds, but in the opposite direction). Relative to the air, the plane is sitting still. Just like you being on a treadmill. You could spring along merrily, relative to the treadmill, but relative to the rest of the room, you are not moving forward.
Thats where your problem lies you can't compare a runner on a treadmill as the runners legs are powered, to an aeroplane-unpowered wheels.
You need to think laterally rather than just at what 'seems' to be happening.
>> Edited by Nic Jones on Tuesday 23 May 18:03
everitj said:Yes, that is exactly what I am saying. You missed a small, but important piece though. If you turned on a jetpack, it would cause you to accelerate. You would pump your legs harder to keep your balance. If the treadmill also accelerates to exactly match your speed at all times, you would run faster, your legs would be pumping harder, but you would still be running in place.
Yes but your missing the point, imagine running on a treadmill in the gym, then turning on a jet pack on your back... what your saying is... If you ran fast enough you would stay still....
Because the treadmill also accelerated. As long as the speeds match, you ain't going anywhere. -v + v = ? (Yup, zero).
The question says that the treadmill matches the wheel speed at all times.
orgasmicliving!! said:
Yes but your missing the point, imagine running on a treadmill in the gym, then turning on a jet pack on your back... what your saying is... If you ran fast enough you would stay still....
Because the treadmill also accelerated. As long as the speeds match, you ain't going anywhere. -v + v = ? (Yup, zero).
The question says that the treadmill matches the wheel speed at all times.
I think you might have been that girl in my A-level class
SamHH said:
I thought to take off the plane would need air flowing over the wings to give it lift.
If it doesn't move- mega conveyor belt cancels out forward movement from engines- how will it take off.
Blueyes
2 O levels- geog and english.
Degree in ice cream making.
It is moving forward. The conveyor belt cannot stop the plane moving forward.
O.K. I'll accept that but can you explain why not? If the belt moves fast enough it should. (sorry I'm so thick)
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