Stupid physics question

[Tilda]

You're all missing the big question here.

Could this , obviously huge, conveyor belt be used to remove all the excess fat in americans at the same time?

<sarcasm> but but but they wont have any airspeed, so they wont burn any fat?!?!!!111213434

 

[ECA]

<sarcasm> but but but they wont have any airspeed, so they wont burn any fat?!?!!!111213434

We could get a really big hairdryer at the end of the conveyor belt.

 

[ECA]

I think the following pic sums things up.

 

[Xgkkp]

A hovercraft isn't on wheels though, so a converyor belt can't ever cancel out the forward motion of the hovercraft where as a conveyor belt (if it were very special) could cancel out rotating wheels.

Ahah! except the wheels aren't mechanically connected to the plane so it doesn't matter what the wheels are doing, the plane itself can do something different.

In this case:

(A wooden trolley is a block where the wheels can run free). Imagine holding it still whilst the conveyor belt moved.
What happens if the conveyor belt speeds up in a similar manner to the question, when you slowly pull the trolley?
(note that letting it go would mean that it fell backwards, before anyone points that out, however this would be due to friction being the only force and the wheels would still spin faster than it would be moving backwards)

Are you claiming that you would never be able to move it forwards at all?

 

[Jupitus]

The only thing that is counteracting the engines is friction on the wheels. Once the jet engines kick in (and the brakes aren't on) the friction force is DWARFED by the engine thrust. Is scenario 1 assuming that the wheels are rusty ? Or is it assuming that the conveyor is running several times faster than the plane would otherwise be moving therefore the force of friction is multiplied by this amount exactly cancelling it ?

Are you agreeing that IF the conveyor moves fast enough that you agree the plane won't gain any air speed hence will not take off?

 

[Jupitus]

Ahah! except the wheels aren't mechanically connected to the plane so it doesn't matter what the wheels are doing, the plane itself can do something different.

In this case:

(A wooden trolley is a block where the wheels can run free). Imagine holding it still whilst the conveyor belt moved.
What happens if the conveyor belt speeds up in a similar manner to the question, when you slowly pull the trolley?
(note that letting it go would mean that it fell backwards, before anyone points that out, however this would be due to friction being the only force and the wheels would still spin faster than it would be moving backwards)

Are you claiming that you would never be able to move it forwards at all?

This analogy is invalid because there is an external anchor to the trolley. A better analogy would be to strap a propellor to the trolley which spins to gain forward thrust.

Now, with the propellor spinning, something moves the conveyor belt to effectively hold the trolley in the same spot in 3 dimensions. Are you saying that would not be possible?

 

[Tom]

Yes he is saying it would not be possible, and hes correct, so long as the wheels do not provide any propulsion.

God its simple, think of the same scenario but get a helicopter involved, and chain it to the aircraft. Get the chopper to pull the aircraft, its the same fecking principle!

 

[Xgkkp]

This analogy is invalid because there is an external anchor to the trolley. A better analogy would be to strap a propellor to the trolley which spins to gain forward thrust.

No, it is not, and there isn't. all you are providing is a force, not an anchor, a force capable of being overcome. It doesn't matter if the force is on the trolley or on a string attached to it, it's still a force.

Okay, let's go one level lower. Do you accept that the plane can be perfectly still with the wheels spinning? (I should hope you do).

Now, what happens to the wheels if you move it forwards slightly whilst they are spinning.... they spin a little faster!

With the plane traveling forwards and the belt traveling backwards at the same speed, the image is identical.

God its simple, think of the same scenario but get a helicopter involved, and chain it to the aircraft. Get the chopper to pull the aircraft, its the same fecking principle!

This is also a good example.

Edit:

 

[Jupitus]

So in the original question/scenario, what is the equivalent of the helicopter/string being held?

 

[Xgkkp]

Yes he is saying it would not be possible, and hes correct, so long as the wheels do not provide any propulsion.

Actually to be pedantically correct that situation is possible, but the propellor would only be spinning fast enough to balance the force due to friction (reasonably slowly). Slower than that, it would fall back, and faster it would move forwards.

 

[Xgkkp]

So in the original question/scenario, what is the equivalent of the helicopter/string being held?

The engines of the plane

 

[Jupitus]

Actually to be pedantically correct that situation is possible, but the propellor would only be spinning fast enough to balance the force due to friction (reasonably slowly). Slower than that, it would fall back, and faster it would move forwards.

So your argument is based on the sudden thrust of the engine meaning the conveyor belt could not keep the plane stationary in 3D ?

 

[Tom]

If there are people who have read this far and still have not grasped it, then they never will tbh.

 

[Jupitus]

If there are people who have read this far and still have not grasped it, then they never will tbh.

You seem to be implying me with that comment... just to be clear, I grasp perfectly well your argument Tom, but I can see that it is flawed... do try not to treat me like an idiot please.

 

[Xgkkp]

So your argument is based on the sudden thrust of the engine meaning the conveyor belt could not keep the plane stationary in 3D ?

No, and that comment I made is more of an aside than directly pertinent to the discussion really. I have no idea where you would get that implication from in the first place anyway.

Also, if you will notice, when I said pulling I said slowly, and even bolded that fact.

So yeah, is your argument that in the case of the helicopter pulling it, it will still not move? (this would of course, be assuming that the helicopter is providing a purely horizontal force - it would be cheating otherwise).

 

[Tom]

You seem to be implying me with that comment... just to be clear, I grasp perfectly well your argument Tom, but I can see that it is flawed... do try not to treat me like an idiot please.

I'm not treating you like an idiot. I don't comprehend hyperbolic equations, no matter how hard I studied they just never worked for me. I just didn't 'get it'. I can't even do quadratic equations ffs. Now I can do plenty of other things that other people can't so it doesn't worry me. Nobody calls me an idiot because of it.

 

[Jupitus]

So yeah, is your argument that in the case of the helicopter pulling it, it will still not move? (this would of course, be assuming that the helicopter is providing a purely horizontal force - it would be cheating otherwise).

Nope - of course it would move, but it is not analagous with the plane providing it's own propulsion.

 

[Tom]

Nope - of course it would move, but it is not analagous with the plane providing it's own propulsion.

You are completely and utterly wrong. The helicopter in this instance is providing exactly the same function as the engines on the wing. The fact that its connected via a chain, and not an aluminium wing, is totally irrelevant.

 

[Xgkkp]

Nope - of course it would move, but it is not analagous with the plane providing it's own propulsion.

What about

Analogous enough for you?

 

[Jupitus]

Re-thinking the would the chopper on a string move and the difference is the fact that the chopper not only provides a horizontal force, but also a vertical one, not on the plane per se, but on itself. You want to include the chopper for your analogy then you need to add it's weight to the plane and the forces being applied... having it floating and able to exert and external force breaks the model.
This is all boiling down to the grip the tyres have on the strip and whether the forces in question would be enough to keep the wheels glued to the moving conveyor or not. I maintain that if the conveyor speeds up in accordance with the original question and thw wheels stay in contact with the strip (i.e we do not assume they will 'slip') then the conveyor will maintain the plane in a static position in 3D.

 

[Xgkkp]

I'm gonna break this into two parts

Re-thinking the would the chopper on a string move and the difference is the fact that the chopper not only provides a horizontal force, but also a vertical one, not on the plane per se, but on itself. You want to include the chopper for your analogy then you need to add it's weight to the plane and the forces being applied... having it floating and able to exert and external force breaks the model.

For a start, I pointed out myself that the helicopter would have to apply a purely horizontal force (relatively easy, just put a pulley! That way the chopper only applies a vertical force, and the plane only gets a horizontal force... though really this shouldn't need to be explained). Secondly weights have nothing to do with the question at all and considering them will do nothing.

The only force that needs to be overcome here is the force of friction on the contact between the wheels and the planes undercarriage - a force that is negligibly small in the first place.

So are you now saying that the chopper couldn't move the plane?

This is all boiling down to the grip the tyres have on the strip and whether the forces in question would be enough to keep the wheels glued to the moving conveyor or not. I maintain that if the conveyor speeds up in accordance with the original question and thw wheels stay in contact with the strip (i.e we do not assume they will 'slip') then the conveyor will maintain the plane in a static position in 3D.

Do you understand the difference between 'physically connected' and 'mechanically connected'? Every analogy over the past couple of pages has been equally valid, from the helicopter to the hovercraft. The hovercraft is an especially relevant example because the craft itself is not mechanically connected to the movement of the ground.... and neither is a plane!
The only force that needs to be overcome here is the force of friction on the contact between the wheels and the planes undercarriage - a force that is negligibly small in the first place. The only force 'gluing' the wheels to the belt is that of gravity, also irrelevant to the question.

 

[Trem]

Stupid fucking science.




Stupid aeroplanes.



Thats my answer.

 

[Jupitus]

The only force that needs to be overcome here is the force of friction on the contact between the wheels and the planes undercarriage - a force that is negligibly small in the first place.

Wrong - the friction between tyres and conveyor belt also applies.

 

[Xgkkp]

Wrong - the friction between tyres and conveyor belt also applies.

Why?

 

[Will]

Wrong - the friction between tyres and conveyor belt also applies.

Rolling resistance for slick tyres is minimal.

 

[tris-]

Why?

reading this whole thing i have changed my answer to yes it will fly.

being a novice in science (only upto a level physics), i can give me simplified reason for it -

think of the wheels purley as propping the plane up.
then imagine the jet engines as having rope wound around their core. then some rope is tied to a pole at the end of the conveyor.

as the core of the engine spins, it winds its self forward. the wheels are not their for anything except to prop the plane up.
the engine is basically doing this, except its air that its pulling through making the plane move forward.

 

[Jupitus]

I suspect you guys are gonna like this - biggest climb down in a long time

The plane will take off.... my line of thinking from quite early on has neglected the stated fact that the conveyor matches the speed of the plane. The plane would NOT take off if the conveyor magically spun fast enough to prevent it doing so, but this would be a damned sight faster than the plane is moving.

So - there you have it. I was wrong

*nips off and edits original question and poll results and quickly closes the thread and removes all evidence thereof

 

[Trem]

ADMIN ABUSE!!!

 

[Will]

*nips off and edits poll results

Snap.

 

[Scouse]

For a start, I pointed out myself that the helicopter would have to apply a purely horizontal force (relatively easy, just put a pulley! That way the chopper only applies a vertical force, and the plane only gets a horizontal force... though really this shouldn't need to be explained

This doesn't work unless the pulley is also on the conveyor belt.

The pulley would be going backwards at the same speed as the conveyor belt whilst pulling the plane to it.

Unfortunately the pully would pull the plane into itself (whilst the plane was stuck in exactly the same position it started).

You can't use examples of external forces acting on the plane.