You have a plane and a conveyor belt.

[cKGunslinger]

Originally posted by: Adam8281
Yes, of course the plane would take off - and here's another way to envision it:

Suppose a plane is flying through the air at 500 mph. Suppose, also, that there is a 10 mile long treadmill up in the air which is spinning 500 mph in the opposite direction of the plane's movement. And suppose the flying plane can fly over the treadmill and touch its wheels upon it, while continuing to have its engines going. What would happen? Would the treadmill stop the plane when the 500 mph plane touched its wheels to it? No, of course not. Instead, the plane would continue to fly at 500 mph, and its wheels would be spinning at 1000 mph (500 mph in reaction to the spinning treadmill beneath it + 500 mph because the plane is moving at 500 mph.) The treadmill would not STOP the plane because the source of the plane's movement is not the WHEELS but the ENGINES. A plane can travel 500 mph even if its wheels are spinning at 1000 mph or 0 mph. This is unlike a car, which only can travel at 60 mph when its wheels are moving at 60 mph, because the source of a car's movement is the wheels.

Consider, again, the mile-high treadmill example, but this time imagine the treadmill is spinning in the SAME DIRECTION as the plane, but at 8000 mph. Say the plane flew over the treadmill and had its wheels touch the treadmill? Would the plane get an amazing power boost, and hit 8000 mph? No, of course not, instead it would continue to travel at 500 mph while it's wheels started spinning like mad tops and probably disentegrate.

Heresy! Burn the witch!

 

[NanoStuff]

Originally posted by: JujuFish

Originally posted by: NanoStuff

You're right about the cog example being a good one. However, you're wrong in the part I bolded. With two different sized cogs, one will always be faster than the other. It shows the inconsistency with your interpretation of the OP.

My mistake, badly worded. I meant to imply that the speed at the surface would be the same for both regardless of their respective size.

As would it if a plane took off on a runway.

Yes, but again the axis of the lower cog is stationary, just like the 'axis' on the belt. Unlike a runway, the surface of the cog would move in relationship to an observer on a static surface around it. The relatively speed between the belt and the wheels would be the same, the only difference would be that the belt (the 'world' the plane is on) would move backwards, effectively keeping it still to an external point of reference.

 

[JujuFish]

Originally posted by: NanoStuff

Originally posted by: JujuFish

Originally posted by: NanoStuff

You're right about the cog example being a good one. However, you're wrong in the part I bolded. With two different sized cogs, one will always be faster than the other. It shows the inconsistency with your interpretation of the OP.

My mistake, badly worded. I meant to imply that the speed at the surface would be the same for both regardless of their respective size.

As would it if a plane took off on a runway.

Yes, but again the axis of the lower cog is stationary, just like the 'axis' on the belt. Unlike a runway, the surface of the cog would move in relationship to an observer on a static surface around it. The relatively speed between the belt and the wheels would be the same, the only difference would be that the belt (the 'world' the plane is on) would move backwards, effectively keeping it still to an external point of reference.

And this is where you show your lack of knowledge in physics.

 

[NanoStuff]

Originally posted by: jagec

Originally posted by: NanoStuff
This friction is what gives the tire traction, and this traction is what inhibits the plane's momentum on a moving belt.

I'm sorry, but that simply isn't the case. Rolling resistance and traction are two ENTIRELY different things.

I don't believe I said otherwise.

Originally posted by: jagec
The cog's a bad example, because for a cog system to work, both cogs have to be bolted into place on the same machine, which implies a transfer of forces that is not in place in the OP.

Not necessarily. You bolt the bottom cog and you keep the top cog free, the point would still be the same. If both are rotating at the same speed, the top cog would not move forward even if it's otherwise unrestricted.

 

[NanoStuff]

Originally posted by: JujuFish

Originally posted by: NanoStuff

Originally posted by: JujuFish

Originally posted by: NanoStuff

You're right about the cog example being a good one. However, you're wrong in the part I bolded. With two different sized cogs, one will always be faster than the other. It shows the inconsistency with your interpretation of the OP.

My mistake, badly worded. I meant to imply that the speed at the surface would be the same for both regardless of their respective size.

As would it if a plane took off on a runway.

Yes, but again the axis of the lower cog is stationary, just like the 'axis' on the belt. Unlike a runway, the surface of the cog would move in relationship to an observer on a static surface around it. The relatively speed between the belt and the wheels would be the same, the only difference would be that the belt (the 'world' the plane is on) would move backwards, effectively keeping it still to an external point of reference.

And this is where you show your lack of knowledge in physics.

And this is where I'm about to stop responding to you due to your lack of debating skills.

 

[God On Alcohol]

since this is in off topic forum, 196 more posts till 100 in this thread!

 

[CallMeJoe]

Originally posted by: NanoStuff
Actually, the OP was stating that the conveyor belt would spin in proportion to the movement of the wheels, and in one interpretation the end result just happens to be that the belt would negate the thrust of the engine. Doesn't have to be a ridiculously powerful conveyor belt, just as powerful as the thrust of the plane.

The problem with the OP's concept is that it does require an infinitely powerful conveyor belt. The wheels on the aircraft are not directly driven, so they will not begin to turn until the aircraft starts to roll forward on the conveyor. This means the aircraft will be moving relative to the entire conveyor assembly, so the belt will always slightly lag behind the wheel speed. Since the conveyor is supposed to move in the opposite direction at the same speed as the tires, the belt would have to accelerate almost instantly to infinite speed.

The problem as presented is almost as absurd as the fact that people are still arguing the question 800+ posts later.

 

[JujuFish]

Originally posted by: NanoStuff
And this is where I'm about to stop responding to you due to your lack of debating skills.

It's not my so-called lack of debating skills, it's your lack of knowledge in physics. You state something is impossible, when there is no basis for it. You're just saying it. Physics disagrees with you.

 

[NanoStuff]

Originally posted by: CallMeJoe

Originally posted by: NanoStuff
Actually, the OP was stating that the conveyor belt would spin in proportion to the movement of the wheels, and in one interpretation the end result just happens to be that the belt would negate the thrust of the engine. Doesn't have to be a ridiculously powerful conveyor belt, just as powerful as the thrust of the plane.

The problem with the OP's concept is that it does require an infinitely powerful conveyor belt. The wheels on the aircraft are not directly driven, so they will not begin to turn until the aircraft starts to roll forward on the conveyor. This means the aircraft will be moving relative to the entire conveyor assembly, so the belt will always slightly lag behind the wheel speed. Since the conveyor is supposed to move in the opposite direction at the same speed as the tires, the belt would have to accelerate almost instantly to infinite speed.

They will begin to turn in direct proportion to the rotation of the wheels if that is your interpretation of the question. The plane will never have a chance to move forward as the belt will instantly compensate.

 

[NanoStuff]

Originally posted by: JujuFish

Originally posted by: NanoStuff
And this is where I'm about to stop responding to you due to your lack of debating skills.

It's not my so-called lack of debating skills, it's your lack of knowledge in physics. You state something is impossible, when there is no basis for it. You're just saying it. Physics disagrees with you.

I stated the 'basis' for it, you just didn't understand it or agree with it. Because you cannot make a counter-argument, I'm assuming the former.

 

[JujuFish]

Originally posted by: NanoStuff

Originally posted by: JujuFish

Originally posted by: NanoStuff
And this is where I'm about to stop responding to you due to your lack of debating skills.

It's not my so-called lack of debating skills, it's your lack of knowledge in physics. You state something is impossible, when there is no basis for it. You're just saying it. Physics disagrees with you.

I stated the 'basis' for it, you just didn't understand it or agree with it. Because you cannot make a counter-argument, I'm assuming the former.

I must have missed this. Explicitly state your basis for how the conveyor belt moving backwards keeps the plane in place.

 

[CallMeJoe]

Originally posted by: NanoStuff
They will begin to turn in direct proportion to the rotation of the wheels if that is your interpretation of the question. The plane will never have a chance to move forward as the belt will instantly compensate.

The problem is that the wheels will not even begin to turn until the body of the aircraft has motion relative to the conveyor.

 

[NanoStuff]

Originally posted by: CallMeJoe

Originally posted by: NanoStuff
They will begin to turn in direct proportion to the rotation of the wheels if that is your interpretation of the question. The plane will never have a chance to move forward as the belt will instantly compensate.

The problem is that the wheels will not even begin to turn until the body of the aircraft has motion relative to the conveyor.

There are two interpretations to the question. One is that the belt will move in reverse at the rotational/angular speed of the wheels, and the other is that it will move at the forward speed of the plane/wheels.

If I understand you right, you're referring to the latter, in which case I agree with you. The belt would move backwards, the wheels would rotate twice their normal speed and the plane would take off.

 

[NanoStuff]

Originally posted by: JujuFish

Originally posted by: NanoStuff

Originally posted by: JujuFish

Originally posted by: NanoStuff
And this is where I'm about to stop responding to you due to your lack of debating skills.

It's not my so-called lack of debating skills, it's your lack of knowledge in physics. You state something is impossible, when there is no basis for it. You're just saying it. Physics disagrees with you.

I stated the 'basis' for it, you just didn't understand it or agree with it. Because you cannot make a counter-argument, I'm assuming the former.

I must have missed this. Explicitly state your basis for how the conveyor belt moving backwards keeps the plane in place.

I thought I made my argument very clear, but sure I'll try again.

If the rotational speed of the wheels is 1m/s, you have forward movement of 1m/s (that's +1m/s) of those wheels.

If you have a belt that moves backwards at 1m/s, you have reverse movement of 1m/s (that's -1m/s)

If you add the rotational speed of the wheel to the rotational speed of the belt, your end result is 0m/s. The wheel does not advance forward, nor does anything attached to this wheel.

 

[techs]

Geez, hasn't anyone heard of Isaac Newton?
For each action there is an equal and opposite reaction.
When thrust comes out the rear of the jet the plane moves forward an equal amount.
The ony thing that would prevent it would be an equal thrust to in the opposite direction.
If the wheels were cemeted to the ground then that would in effect mean the planes thrust would be transferred to the earth and the earth would actually be affected by the planes thrust.
In your question the treadmill is not exerting thrust on the plane because you are asserting a complete frictionless turning of the planes wheels.
So, yes, the plane will move forward and when it reaches an airspeed that supports enought lift the plane will take off.
Absolutely.

 

[JujuFish]

Originally posted by: NanoStuff
I thought I made my argument very clear, but sure I'll try again.

If the rotational speed of the wheels is 1m/s, you have forward movement of 1m/s (that's +1m/s) of those wheels.

Forward movement is not necessary in relation to angular velocity.

If you have a belt that moves backwards at 1m/s, you have reverse movement of 1m/s (that's -1m/s)

By moving in reverse, it places a torque on the wheels, increasing the angular velocity.

If you add the rotational speed of the wheel to the rotational speed of the belt, your end result is 0m/s. The wheel does not advance forward, nor does anything attached to this wheel.

By your interpretation, adding them together would be adding positive and negative infinity together. Obviously, you've created an impossible situation here. In this nonsensical world, since it obviously doesn't have physics as we understand it, who's to say it does or doesn't take off? It just doesn't work.

 

[jagec]

Originally posted by: NanoStuff
I thought I made my argument very clear, but sure I'll try again.

If the rotational speed of the wheels is 1m/s, you have forward movement of 1m/s (that's +1m/s) of those wheels.

If you have a belt that moves backwards at 1m/s, you have reverse movement of 1m/s (that's -1m/s)

If you add the rotational speed of the wheel to the rotational speed of the belt, your end result is 0m/s. The wheel does not advance forward, nor does anything attached to this wheel.

Except when you turn the belt on to -1 m/s, with the wheels rolling forward at 1 m/s angular velocity, the inertia of the plane keeps them going, meaning the wheels are now rolling at 2 m/s angular velocity. The conveyor sees this and says "Oh Em Gee I gots to speed up now!!1!one!", and is now going at -2 m/s. Well, now the wheels are going at 3 m/s angular...you see the problem.

Unless you can show me how the conveyor transfers force to the BODY of the plane, thus decreasing its momentum, you can't use that interpretation.

Rolling resistance isn't good enough, since that's a tiny fraction of what the aircraft engines can put out.

Originally posted by: techs
Geez, hasn't anyone heard of Isaac Newton?
For each action there is an equal and opposite reaction.
When thrust comes out the rear of the jet the plane moves forward an equal amount.
The ony thing that would prevent it would be an equal thrust to in the opposite direction.
If the wheels were cemeted to the ground then that would in effect mean the planes thrust would be transferred to the earth and the earth would actually be affected by the planes thrust.

Whenever we ask the "won't take off" people to explain where that thrust is coming from, they complain "This is a logic problem, not a physics problem":laugh:

 

[NanoStuff]

-double post-

 

[NanoStuff]

Originally posted by: techs
Geez, hasn't anyone heard of Isaac Newton?
For each action there is an equal and opposite reaction.

Brilliant man, perhaps if he was still alive he could make sense of this for you. Like you said (or he said, any way you want to think of it), "equal and opposite reaction".

Action1: belt moves backwards
Reaction1: plane moves backwards

Action2: plane's thrust moves plane forwards
Reaction2: plane moves forwards

Action1 + Action2 are opposite thus cancel eachother out
Reaction1 + Reaction2 are opposite thus cancel eachother out.

 

[JujuFish]

Originally posted by: NanoStuff

Originally posted by: techs
Geez, hasn't anyone heard of Isaac Newton?
For each action there is an equal and opposite reaction.

Brilliant man, perhaps if he was still alive he could make sense of this for you. Like you said (or he said, any way you want to think of it), "equal and opposite reaction".

Action1: belt moves backwards
Reaction1: plane moves backwards

Action2: plane's thrust moves plane forwards
Reaction2: plane moves forwards

Action1 + Action2 are opposite thus cancel eachother out
Reaction1 + Reaction2 are opposite thus no action takes place.

They are opposite, but they are not equal.

 

[NanoStuff]

-double post- goddamnit

 

[NanoStuff]

Originally posted by: NanoStuff

Originally posted by: JujuFish

Originally posted by: NanoStuff

Originally posted by: techs
Geez, hasn't anyone heard of Isaac Newton?
For each action there is an equal and opposite reaction.

Brilliant man, perhaps if he was still alive he could make sense of this for you. Like you said (or he said, any way you want to think of it), "equal and opposite reaction".

Action1: belt moves backwards
Reaction1: plane moves backwards

Action2: plane's thrust moves plane forwards
Reaction2: plane moves forwards

Action1 + Action2 are opposite thus cancel eachother out
Reaction1 + Reaction2 are opposite thus no action takes place.

They are opposite, but they are not equal.

Depends on your interpretation

 

[SparkyJJO]

The plane increases it's thrust and the wheels begin to rotate. The belt compensates for the rotation of the wheels in reverse, as in the belt moves in reverse exactly as fast as the wheels move forward.

meaning the plane physically doesn't move anywhere....

And if it matters, it's a nice sunny day and you have good tires, so you get perfect traction on the belt at all times.

And that doesn't matter at all because.....

Your plane also happens to be very powerful and you can give it as much thrust as you like, but the source of thrust is at the back of the plane so it never provides airflow over the wing.

There is the deciding factor. No airflow means no lift, and no lift means the plane won't take off.

 

[JujuFish]

Originally posted by: NanoStuff

Originally posted by: JujuFish

Originally posted by: NanoStuff

Originally posted by: techs
Geez, hasn't anyone heard of Isaac Newton?
For each action there is an equal and opposite reaction.

Brilliant man, perhaps if he was still alive he could make sense of this for you. Like you said (or he said, any way you want to think of it), "equal and opposite reaction".

Action1: belt moves backwards
Reaction1: plane moves backwards

Action2: plane's thrust moves plane forwards
Reaction2: plane moves forwards

Action1 + Action2 are opposite thus cancel eachother out
Reaction1 + Reaction2 are opposite thus no action takes place.

They are opposite, but they are not equal.

Depends on your interpretation

No, the whole action and reaction is about forces, not about velocity. There isn't any interpretation here. The conveyor belt does apply a force, however it is very small and easily compensated by the plane.

 

[mugs]

Originally posted by: NanoStuff

Originally posted by: techs
Geez, hasn't anyone heard of Isaac Newton?
For each action there is an equal and opposite reaction.

Brilliant man, perhaps if he was still alive he could make sense of this for you. Like you said (or he said, any way you want to think of it), "equal and opposite reaction".

Action1: belt moves backwards
Reaction1: plane moves backwards

Action2: plane's thrust moves plane forwards
Reaction2: plane moves forwards

Action1 + Action2 are opposite thus cancel eachother out
Reaction1 + Reaction2 are opposite thus cancel eachother out.

Wait - do you actually think the bolder part is true? I'm not quite sure if I've read your reasoning on WHY you think the conveyor belt can possibly match the speed of the wheels and keep the plane stationary. The only valid explanation for why the plane would not be able to take of is that the wheels would explode due to the infinite acceleration. If you think that it is possible for the conveyor belt to hold the plane in place while the wheels are intact, you are wrong. It is not possible. That is proven by the fact that planes are able to move on solid ground. To the plane there is no real difference between moving on a treadmill and moving on solid ground (until the wheels explode/melt/whatever).

IMPORTANT: The conveyor belt's ability to hold the plane in place is limited to the friction in the wheels. It can't just magically hold the plane in place because the question says it always moves at the same speed as the rotation of the wheels. It just doesn't work that way in the physical world.