How do you not get this? The speed of the plane is irrelivent! The wheels can spin at whatever speed they want, the plane will still move forwards.
Earth spinning
- Thread starter mollymoo
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How do you not get this? The speed of the plane is irrelivent! The wheels can spin at whatever speed they want, the plane will still move forwards.
How can you not get this. How can the plane move forwards without it's wheels moving at a different speed to the treadmill? It's impossible unless the plane skids.
Soldato
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I vote we ban the person who started this argument again!
Neodude: I love your argument, you are right in terms of the question as it was put here. The way it is usually put is just a trick question to make people realise that the wheels do not drive a plane forward and think about multiple forces so why not a trick answer to a trick question when the question is worded wrong.
Eww that's a horrible scentence even for me.
Eww that's a horrible scentence even for me.
Soldato
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No....
It's why if you have the a free moving treadmill, (so the wheels obviously would match the planes wheels) the plane will still take off.
The wheels mean bupkis. They're not powering the plane, that'd be the job of the big noisy things stuck on the wings.
*EDIT*
Wait, why am I getting involved?
The wheels can't move faster. The question doesn't allow it!
Associate
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Not entirely true. If the treadmill could exactly match the rotational speed of the wheels, regardless of how fast they spin, there is no possible way for the plane to move, assuming the wheels don't slip, or get torn from the undercarriage.
This is because all the thrust must be used to get the wheels moving relative to the treadmill, which is very easy if the treadmill only moves slowly, such as at the planes takeoff velocity, but is obviously impossible if the treadmill always matches the wheel speed, since the net forces will always balance in this case.
Even if the wheels are free wheeling, which they are, there is still a small lateral force on the rest of the plane, due to the friction between the wheel and the ground, this must be overcome before the plane can move. Again, easy on the ground or a slow treadmill, impossible on a speed matching treadmill.
Caveats: It is more than likely impossible to get a treadmill moving fast enough to do this, and i doubt that the wheels could spin fast enough before exploding. However, assuming everything is 'ideal', a treadmill can stop a plane from taking off.
Summary: Wheel rotational speed matching treadmill + caveats: plane can't take off (probably not possible in real life)
Regular treadmill at planes takeoff velocity: plane takes off.
Last edited:
Dan Dan: Read the question as it was stated in this thread and your last post again.
Technically, the way the question has been phrased with regard to the treadmill and wheel speed being matched, then neodude is correct, if it constantly matched the speed perfectly it matters not one bit where the forward thrust force comes from, the wheel could not move forward without skidding along, to do so requires a difference in the speeds which is outside the confines of the question. Then the debate turns to whether the jets/props could overcome the friction and induce that skid. Either that or you have the situation of the treadmill and wheels both tending towards infinite speed in an incredibly short amount of time, which clearly could not happen without something breaking.
In the way the question is popularly phrased, relating treadmill to plane speed, then the plane takes off easily.
In the way the question is popularly phrased, relating treadmill to plane speed, then the plane takes off easily.
But where is no way the treadmill will reach the same speed as the wheels, if the treadmill goes at speed X, the wheels will always be travelling at X+2 (or whatever speed).
The idea of the friction eventually reaching the same force as the thrust from the engines is sound, but impossible, so irrelivent.
The idea of the friction eventually reaching the same force as the thrust from the engines is sound, but impossible, so irrelivent.
That's a different situation to the question as originally stated though, whereby the treadmill and wheel speeds are constantly exactly the same.
I didn't say it was possible. I have said from the start of this vastly growing argument that the situation has no basis in reality, I'm merely going by the question. In the question stated it is impossible for the plane to move (unless it has enough power to skid, and even then it's hit or miss whether it reaches takeoff speed).
Associate
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Actually, this is no different to the toy car on a treadmill being held in place by a finger,
push harder = car goes forward
turn up treadmill = car stops again
repeat ad nauseam.
push harder = car goes forward
turn up treadmill = car stops again
repeat ad nauseam.
I see, well the question itself is therefore impossible. But yes, as the question is wrong, then what you said is correct, I misread it.
Pretty much yes, as it was phrased in this thread attempting to apply any inkling of reality to it completely fails before you even begin
Soldato
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I didn't seriously think people would start arguing over it again...
You joined 5 years ago, and don't know OCUK well enough to realize that people would? You deserve a ban for not knowing us well enough!
