conveyor belt and plane answered at last ??

[crank39]

OK. I'll do just that.

The conundrum does not state that the conveyor's movement keeps the plane in the same position relative to the ground, just that it moves in the direction opposite to any movement of the airplane.

While the argument about the speed of the conveyor belt in the opposite direction preventing the plane from accelerating initially seems logical, it is irrelevant to what is happening to the plane, because the engine is acting on the air.

I'll try again, just a yes they will or no they won't will do...

So if i put a model plane on a dining table and pulled the table cloth out from under it are you suggesting the wheels would not rotate the opposite way?

 

[doitall]

What I meant was that the speed of the conveyor is not important, the plane will still take off.

Not if the wheels can't travel faster the belt it wont.

 

[securespark]

What's the tablecloth scenario got to do with what I posted?

 

[doitall]

Doitall are you 12?

My age is off topic

I know when you're loosing the argument as it gets personal.

 

[securespark]

What's the tablecloth scenario got to do with what I posted?

Why don't you just tell us what you're getting at?

 

[Mw Roofline]

Doitall are you 12?

My age is off topic

I know when you're loosing the argument as it gets personal.

Lol, just messing with you, I'm as intrigued about all this as you are. I'm no physisist (Can't spell physisist )

But if I refer to my previous post:

The easiest way to understand all this (I haven't read all the last trillion pages so someone may have already mentioned it) is imagine you are the plane on roller skates and the runway is one of those check-out supermarket moving things but it's in reverse mode.

You stand still with me next to you standing on the floor and when the belt starts to move, you also start to move backwards. I stop you from moving backwards as I'm right next to you with my hand on your back stopping you still. let's say the belt is going 10 miles an hour.

Marjorie the check out lady cranks up the mph to 20, 30 and 50mph. Your wheels are spinning like crazy but you are stood still still because I'm applying a bit of pressure to your back.

Then marjorie cranks it up to 250mph and all it takes is a gentle push of my hand and I can push you forwards along the conveyor which is doing 250mph, just because it's going faster doesn't mean there is any more pressure on my hand. I start to push you a little more and you move forward easy as pie. It doesnt matter how fast the belt is moving because whatever speed is happening is just getting absorbed up by the wheels going round and round.

I know it's described a bit loose but tell me what is wrong with the above, never mind table cloths and the interpretation of the original question, just tell me where i'm going wrong with the above principle.

 

[securespark]

In desperation, I have turned to t'interwebby to try and help explain the pro-takeoff POV.

See here: http://www.straightdope.com/columns/read/2642/a-plane-is-standing-on-a-runway-no-its-not-heres-why

In particular this quote,

In principle it's possible to accelerate the treadmill at a rate that will exactly counteract any forward force you care to apply. (This is a departure from the original question, which said the conveyor belt compensated for the plane's speed, not its force.)

And here,

one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH. Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way.

 

[doitall]

So there you have it secursparks.

If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH.

The wheels are not allowed to go faster than the conveyor.

Ps, it has nothing to do with force other than it needs a force to stop the plane going backward or to go forwards.

 

[securespark]

You sound a little triumphant!

As you asked me to re-read something you posted in red, so will I.

The original conundrum said the belt will run at the same speed as the plane's wheels.

(...the conveyor belt compensated for the plane's speed, not its force.)

I see you have quietly altered what you wrote about force!

Force is the key to this.

The other key to this is divorcing the wheels from the plane.

I left the last few words off the second quote in my post. They were:

Everything clear now? Maybe not. But believe this: The plane takes off.

Somehow, I know you won't be convinced!

 

[doitall]

My apologise if I changed something it wasn't intentional.

The plane needs a force/energy to go forward or stop itself going backwards, and that is the only relevance to force.

The part you need to understand is the conveyor matching the wheels speed.

So just to wrap it up, as you posted the plane is going 100mph hour and the conveyor is going 100mph in the other direction so the wheels are doing 200mph. Now as you know thats not allowed in the question, they have to match.

The only way that can happen if both are stopped.

The plane cannot take off. in any case it's probably run out of juice by now.

 

[crank39]

My apologise if I changed something it wasn't intentional.

The plane needs a force/energy to go forward or stop itself going backwards, and that is the only relevance to force.

The part you need to understand is the conveyor matching the wheels speed.

So just to wrap it up, as you posted the plane is going 100mph hour and the conveyor is going 100mph in the other direction so the wheels are doing 200mph. Now as you know thats not allowed in the question, they have to match.

The only way that can happen if both are stopped.

The plane cannot take off. in any case it's probably run out of juice by now.

My interpretation of that was that the wheel speed WAS matched with the conveyor in the sense that they were both travelling at 100mph albeit the wheel is measured in rpm equivalent to 100mph, in order for the plane to move forward the wheel rpm would need to increase but the conveyor not to increase mph and in the constraints of the question that is not allowed so the plane would not take off

 

[joe-90]

The question as interpreted is stupid. If the plane engines move forward at 100mph then the conveyor will move back at 100mph. The wheels will therefore travell at 200mph. If you don't like that - forget the question as it is just nonsense.

 

[Mw Roofline]

in any case it's probably run out of juice by now.

Yep and the treadmills fcuked

 

[Deleted member 63160]

My apologise if I changed something it wasn't intentional.

The plane needs a force/energy to go forward or stop itself going backwards, and that is the only relevance to force.

The part you need to understand is the conveyor matching the wheels speed.

So just to wrap it up, as you posted the plane is going 100mph hour and the conveyor is going 100mph in the other direction so the wheels are doing 200mph. Now as you know thats not allowed in the question, they have to match.

The only way that can happen if both are stopped.

The plane cannot take off. in any case it's probably run out of juice by now.

My interpretation of that was that the wheel speed WAS matched with the conveyor in the sense that they were both travelling at 100mph albeit the wheel is measured in rpm equivalent to 100mph, in order for the plane to move forward the wheel rpm would need to increase but the conveyor not to increase mph and in the constraints of the question that is not allowed so the plane would not take off

In reality the conveyor and the wheels would both continue to revolve at similar speeds relative to each other till the plane took off. Good topic though.

 

[securespark]

Be interesting to see what the general opinion is out there - how many reckon it'll take off vs the ones who think it won't.