Brainteaser Options

[camsmith]

If the planes 'speed' is being matched and conteracted by the speed of the conveyer,

Who said anything about counteracted? The fact that the plane is freewheeling over this surface means that the speed of the surface is irrelevant. The wheels just turn faster to keep up with the plane.

[james]

Another version to help you visualise the solution:

Imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily. It doesn't matter how fast the treadmill ends up, your still pulling, the ropes still getting shorter and you will be getting closer to the wall.

As Cam rightly says the action of the conveyor & wheels is irrelevant and does not counteract the forward motion of the plane relative to the earth because you have an external force (the engines) providing that motion.

[jamie]

I think you may need to read the first post again

if you have a car driving at 60 miles an hour, on a convayer belt going at 60 miles an hour in the opposite direction the car is stationary...

the cars speed has been counterated by the conveyer belt. why would it be different for a plane?

[Emily]

can we leave out that plane taking off, we all know it wont take off unless it moves, all we need to work out if how its gonna get up to speed. If your little matchbox car has got a jet engine and is on a mini conveyer that can move as fast as it little wheels then unless there is another force to counteract the weight of the car keeping it on the wheels then the conveyer will keep going faster and faster still doesn't work!

The thing i don't understand is why the wheels end up going faster then the conveyer, because that is what you are saying is it not?

the difference to a plane and a car is that the motion created by the wheels is moving the car, where as the wheels on a plane just let it move, but it would still be the same in the end i reckon

ding! lights come on, sorry i am wrong!

This post has been edited by Emily: Feb 24 2006, 03:48 PM

[james]

J - you are not understanding the difference between the function the wheels on a plane provide and the function they have on a car.

Em - where do you stand on the whole problem now - would it take off or not?

[Emily]

i cant even think if a way to explain it but as i've just said a car uses propulsion through the wheels, pushing the ground away, the plane used the air.

imagine you have wheels, and you have a big rope in front of you (the rope is the air) if you pull yourself along the rope it doesn't matter how fast the conveyer is going you will move along the rope, the wheels will just spin faster to keep up with you even if the conveyer spins faster too. you plane is taking air from the front and putting it behind itself in the same way you pull in the rope and push it away behind you

apologies to james, its hard to explain and i didn't understand

[camsmith]

It's all about relative speeds...

A car's speed is measured relative to the ground immediately below its wheels.

A plane's speed is measured relative to the air around it.

I agree that if you put a standard motor car in the place of the plane, it would absolutely not move. This is because the car can only move if its tyres provide friction with the ground. As the wheels go round, the car moves across the ground.

However, we are talking about a plane. The plane moves because it forces a lot of air backwards. The mass of air being forced backwards exerts the same force on the plane to move forwards through the air.

The fact is that normally, the air and the ground normally move at roughly the same speed and therefore we perceive that the same thing is happening. It is not. The plane is moving through the air, the car is moving across the ground.

If we start moving the ground, the car will be affected, but the plane will not.

This is exactly the same as saying that if a wind blows, the plane will be affected, but the car will not. This is why planes always take-off and land into the wind.

[james]

No worries hun (in case anyone wonders what we are talking about, yes we did just have an argument about this)

[Emily]

we're about to have another now that you have told everyone about it

[Doctor]

My brain hurts


I took one look at this and thought; "sounds tricky but the belt has no effect on the plane as the engines are providing thrust and not the wheels."

It seemed so self-evident I didn't even post

I wouldn't mind but I'm the one who's brain is supposed to be addled from years of frying it in various ways. All the young people with young, fully functional brains seem to be having......trouble.

I suggest getting a treadmill, an wheelchair and a fire extinguisher and trying it yourselves.

And filming the result

Just hang on to the wheelchair as you may need it afterwards.

[camsmith]

I reckon we should use the treadmill, rollerblades, fire extinguisher and hang glider...

If you think this is confusing, try keeping up with quantum computing

BTW, don't take this to mean that I can understand what they are going on about...

This post has been edited by camsmith: Feb 24 2006, 05:17 PM

[jamie]

I dont feel confused, I just think youre all wrong!

[paul]

A plane cannot take off without air moving over the wings either by forward motion or by some freak wind. FACT. End of story!

[Emily]

will you all LISTEN and STOP talking about the bloody wings and how the plane takes off, its irrelevant, the only argument we have here is how the plane is going to get up to speed. We all know how a plane has to take off and we're not saying its going to happen any other way.

Our argument is that the plane will move from the conveyer and wont stay in one place, the plane will either run off the end of the conveyer and on to the run way or the conveyer is really long and the plane moves along it. What they are saying is the plane will move along to conveyer not take off from stand still.

[quaker]

computer says no