not if the trains going at a constant speed its not
Earth spinning
- Thread starter mollymoo
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not if the trains going at a constant speed its not
You are still wrong thoThe thrust of the jet engines is independent of the wheels and the treadmill, the jet engines always win.
I think a 747 at full thrust on a treadmill travelling backwards at 500,000mph would have trouble taking off.
No, you're the one imposing conditions on the tyres. That they have infinite friction with the treadmill. The treadmill is the only accellerant for the wheels, so it will just accellerate infinitely as it tries to match the speed of the wheels, or it would remain stationary.
The addition of the force of the Jet engines would make the wheels spin faster than the treadmill (which can't happen in this example) or make the wheels skid over the treadmill. they would still be moving at the same speed, but the wheels will move relatively to the treadmill.
they did it on mythbusters IIRC. it flew
theres no reason why it wouldnt. is just the same as a plane taking off from water
So we have to use a real world plane on the fictional 500k mph treadmill? Even so, my previous post would still apply and the plane could take off, unless you bring infinite friction between the wheels and the treadmill into play.
It depends how you define the terms in the original question, considering the speed the wheels are moving at the centre of the hubs in relation to the ground is probably more valid than your construction as yours is a logical impossibility.
But you can apply the rules of physics to say whether it would or not. One way or another the matched speeds question either breaks them with its restrictions or it can still fly.
I'm not imposing infinite friction. At no point did I mention infinite friction. I'm thinking an average airliner sized plane. When arguing my point I'm generally thinking in 757 terms. I know for a fact that with the parking brake set a 757 can go to full thrust without moving (no gliding along on it's wheels).
I concede that for a fighter or lighter aircraft with a high power-weight ratio it would be possible in this case for that to happen.
I think he is saying that to take off the plane's wheels will infact move faster than the treadmill... but that breaks one of the rules so your takeoff does not apply and so he wins the argument...
...but it isn't traveling backwards, because it's on a treadmill it's absolutely stationary. The engines therefore don't need to work against any other forces as the air that they work on is stationary too and will generate forward movement.
In that case it's just the same as the original question. The plane would take off. I was assuming by wheelspeed he meant the rotational speed of the wheels.
Only if you ignore air resistance.
I'm saying that if the treadmill is travelling backwards at 500,000mph it will generate a force backwards on the plane against the push from the engines.
So you are imposing arbitrary restrictions on the air craft, relatively speaking giving infinite friction, a 757 but a treadmill capable of accellerating to 500k mph. You started by saying that in the question it was not possible for the plane to take off, you've just conceded that's wrong, my work here is done
Well if you're moving the treadmill backwards relative to a defined point in space then of course it won't be able to take off.
But in this question the treadmill itself, the air around it and the plane start stationary, the only thing moving is the treadmill belt.
The treadmill belt and wheel speed is an inconsequential element in the system if all other objects and fluids are stationary (apart from the moving parts of the engines and aircraft itself of course)
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no it wont. the wheels will just spin under the plane , the only force will come from friction in the wheel bearings and it will be TINY (admittedly theyd probably melt at that speed quoted)
My assumption was jumping from carriage to carriage on top of a train. Inside a train it will make no difference at all. My bad.