Why the plane takes off in laymans (my) terms

Originally posted by sugiezd
When it's on the ground how else do you want to do it?

Do you understand the difference between air-speed (AS) and ground-speed (GS)?

Yes, I know it. I've been using it. We seem to have introduced a new concept of belt-speed as well.

Damn. I wasn't going to post again. Oh well.

Originally posted by Marsan
A previous post by sugiezd

[quote](Truncated) ... The plane moves in one direction, while the conveyer moves at the same speed but in the opposite direction. Can the plane take off?"

THEY ARE MOVING AT THE SAME SPEED.

This can only mean relative to each other.

The plane cannot, therefore move at a higher speed than the belt BY DEFINITION IN THE ...[text shortened]... e the experiment, you're just wasting our time otherwise.



EDIT: Some spelling edits

PLEASE do us all a favour and re-read the problem.

Where do you get all this verbage about relative to the observer?

A plane is standing on a runway that can move (some sort of treadmill). The plane moves in one direction, while the conveyer moves at the same speed but in the opposite direction. Can the plane take off?"

As the one is on the other, the problem defines them in relation to each other.

Try an English comprehension test if you don't see that.

Originally posted by mtthw
Yes, I know it. I've been using it. We seem to have introduced a new concept of belt-speed as well.

Damn. I wasn't going to post again. Oh well.

I know what you mean - I told myself that I would leave this a few days ago.

The problem is a bone-headed Antipodian who can't see the wood for the trees.

OK, so you accept the definiton of the relationship between plane and belt?

In which case the rest is easy as by definiton in the problem, whatever the GS of the plane on the belt (the belt is effectively the ground), the belt matches it and the AS remains zero.

Should the plane accelerate and the belt not, then the AS and the GS would increase but this is forbidden by the way the problem is stated.

Originally posted by sugiezd
And that is exactly where you are going wrong.

It doesn't matter whether the forward force is acting through the wheels or not. THE WHEELS MUST STILL TURN.

They are turning on the belt - for the plane to move forward relative to a fixed point then they must be turning faster than the belt is moving in the other direction.

As this expressly contradicts the problem as stated then it is impossible.

The wheels roll on the ground or the belt because the plane is moving. How fast they roll is not important.

If the belt moves in the same direction and at the same speed, the plane will be moving and the wheels will not. And if the plane moves fast enough to lift from the surface it will have done so in this case without the wheel turning at all.

Originally posted by mwmiller
The wheels roll on the ground or the belt because the plane is moving. How fast they roll is not important.

If the belt moves in the same direction and at the same speed, the plane will be moving and the wheels will not. And if the plane moves fast enough to lift from the surface it will have done so in this case without the wheel turning at all.

Huh?

Are you saying that if the plane is stationary with repect to the belt but then the belt moves fast enough in the right direction so that the airspeed of the plane passes take of speed and it will fly?

Agreed - your point is what?

Originally posted by sugiezd
Huh?

Are you saying that if the plane is stationary with repect to the belt but then the belt moves fast enough in the right direction so that the airspeed of the plane passes take of speed and it will fly?

Agreed - your point is what?

My point is that the speed of the wheels is not a factor.
The direction or speed of the belt is not a factor.

If the plane pulls itself forward fast enough to achieve lift it will fly.

The belt in this case just happens to be moving in the same direction and at the same speed. (It is not moving the plane. The plane engine is moving the plane.)

Originally posted by mwmiller
My point is that the speed of the wheels is not a factor.
The direction or speed of the belt is not a factor.

If the plane pulls itself forward fast enough to achieve lift it will fly.

The belt in this case just happens to be moving in the same direction and at the same speed. (It is not moving the plane. The plane engine is moving the plane.)

Have you read the original problem?

Sheesh.

Originally posted by sugiezd
Have you read the original problem?

Sheesh.

I certainly have. (wheels are not even mentioned, by the way...)

I think you are visualizing the movement of the plane and the movement of the belt in the same dimension. They are not, and their movement is not relevant to each other.

At any rate I have tried to explain my position in a sensible manner (without adding personal insults, etc...) and now leave it up to you who are reading this to work it out to your own satisfaction.

Originally posted by mwmiller
I certainly have. (wheels are not even mentioned, by the way...)

I think you are visualizing the movement of the plane and the movement of the belt in the same dimension. They are not, and their movement is not relevant to each other.

At any rate I have tried to explain my position in a sensible manner (without adding personal insults, etc...) and now leave it up to you who are reading this to work it out to your own satisfaction.

You're quite right - wheels are not mentioned, silly me.

Of course, if the plane is supported by some magnetic device or even anti-gravity, then you may be right.

Originally posted by sugiezd
You're quite right - wheels are not mentioned, silly me.

Of course, if the plane is supported by some magnetic device or even anti-gravity, then you may be right.

It most likely would be a wheel. The wheel just is not relevant. That's probably why it isn't specifically mentioned in the original scenario.

Originally posted by mwmiller
It most likely would be a wheel. The wheel just is not relevant. That's probably why it isn't specifically mentioned in the original scenario.

Oh come on - what else could it be, seaplane floats, skis?

Originally posted by sugiezd
Oh come on - what else could it be, seaplane floats, skis?

If a seaplane was moving against a strong current would it take off? If the answer is yes, which I suspect it is, then it shows why the answer to the original puzzle was yes.

Originally posted by sugiezd
Oh come on - what else could it be, seaplane floats, skis?

Here's the original statement.

"A plane is standing on a runway that can move (some sort of treadmill). The plane moves in one direction, while the conveyer moves at the same speed but in the opposite direction. Can the plane take off?"



It doesn't really matter if it's wheels, floats or skis. It's irrelevant.

The plane moves in one direction and the conveyer moves at the same speed in the opposite direction.

Stating that the plane moves in one direction is relevant, but it doesn't give enough information to answer the question, so......

My answer is that the plane can take off if it is moving fast enough through the air to lift from the surface.

Originally posted by sugiezd
THE WHEELS MUST STILL TURN.

They are turning on the belt - for the plane to move forward relative to a fixed point then they must be turning faster than the belt is moving in the other direction.

As this expressly contradicts the problem as stated then it is impossible.

Trust us.
You're nearly there.

The belt move backwards at speed x (relative to the ground)
The plane moves forwards at speed x (relative to the ground)
The wheels turn as if the plane were doing speed 2x.

If it were a car, driven by the wheels, the car would be stationary relative to the ground, but at speed x relative to the belt.

But the propeller pulls the plane forward relative to the ground, regardless of what the belt does. All the belt does is make the wheels turn faster.

Originally posted by Ian68
If a seaplane was moving against a strong current would it take off? If the answer is yes, which I suspect it is, then it shows why the answer to the original puzzle was yes.

For god's sake.

Absolutely not given the same conditions, ie relative speed.