A plane on a conveyor belt

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Peter Diffey said:
Its a concept to test you on the basic laws of physics.........failboat?
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It's not though is it? The wording in the OP is meant to deceive, so the question itself lacks any credibility.

If the question were simplified to what it's really getting at, without any of the trimmings - the answer quite simply is "if it has enough velocity, yes - if it lacks enough velocity, no"

There's no need to dress it up.

If you want to test yourself on the basic laws of physics, go take a GCSE Physics exam.
 
The problem that a lot of people have with this is the issue of friction. Scuzi has made it reasonably clear with the bike on the treadmill example, people are equating running on a treadmill to freewheeling on one.

If we take a wheel as a frictionless contact point, which is simplifying the issue slightly, but not overly, any object with a frictionless wheel when on a conveyor belt will remain unmoved by the speed of that conveyor belt.

Let's make this clear, the speed of the conveyor belt has zero effect on the forward or backward motion of this object because it's own frictionless wheel spins in the opposite direction to compensate for the motion of the conveyor.

If we then apply thrust from the engine of the aircraft, we can apply newtonian physics, and look at conservation of momentum with impulse effects. Basically, the mass of air shooting really fast out the back causes the plane to begin to move forward. If it can move forward it can achieve lift and therefore take off.

My only experience in this is a Physics degree btw ;)
 
SpeedFreak said:
The problem that a lot of people have with this is the issue of friction. Scuzi has made it reasonably clear with the bike on the treadmill example, people are equating running on a treadmill to freewheeling on one.

If we take a wheel as a frictionless contact point, which is simplifying the issue slightly, but not overly, any object with a frictionless wheel when on a conveyor belt will remain unmoved by the speed of that conveyor belt.

Let's make this clear, the speed of the conveyor belt has zero effect on the forward or backward motion of this object because it's own frictionless wheel spins in the opposite direction to compensate for the motion of the conveyor.

If we then apply thrust from the engine of the aircraft, we can apply newtonian physics, and look at conservation of momentum with impulse effects. Basically, the mass of air shooting really fast out the back causes the plane to begin to move forward. If it can move forward it can achieve lift and therefore take off.

My only experience in this is a Physics degree btw ;)
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But there's no need for any such explanations.

The answer to the question is...

"if it has enough velocity, yes - if it lacks enough velocity, no"
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The rest of it is not relevant and is unnecessary.
 
Is the confusion not with some people thinking about a runway sized convayor belt and some people thinking about it sitting on a treadmill sized one like the picture above?
 
Oh Deity is this still going on!

THE PLANE WILL TAKE OFF!!!

Irregardless of the ground (ie conveyor belt) moving the plane will not remain stationary it will just move twice as fast relative to the ground but at normal speed RELATIVE TO THE AIR.

That is the important bit as air flow over the wings is what generates lift not speed relative to the ground.

Nearest example would probably be an amphibious plane taking off by traveling upstream of a river. If you ignore any drag due to water resistance then you get a fairly close approximation of a conveyor belt in the form of a river.
 
SpeedFreak said:
The problem that a lot of people have with this is the issue of friction. Scuzi has made it reasonably clear with the bike on the treadmill example, people are equating running on a treadmill to freewheeling on one.

If we take a wheel as a frictionless contact point, which is simplifying the issue slightly, but not overly, any object with a frictionless wheel when on a conveyor belt will remain unmoved by the speed of that conveyor belt.

Let's make this clear, the speed of the conveyor belt has zero effect on the forward or backward motion of this object because it's own frictionless wheel spins in the opposite direction to compensate for the motion of the conveyor.

If we then apply thrust from the engine of the aircraft, we can apply newtonian physics, and look at conservation of momentum with impulse effects. Basically, the mass of air shooting really fast out the back causes the plane to begin to move forward. If it can move forward it can achieve lift and therefore take off.

My only experience in this is a Physics degree btw ;)
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An excellent explanation. I think this vid complements it perfectly :)

http://youtube.com/watch?v=bEyfHwDdXSg&feature=related
 
andyp said:
First comment on that video.

Indeed.

I'm gonna shut up about it now and wait for my answers :)
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Youtube said:
The confusion comes from how the problem is defined. The spirit of the question is not that the plane is travelling at airspeed x and the conveyor belt is travelling at x in the opposite direction (which is Mythbusters take on the matter), it is that the belt and plane are working against each other such that the plane is stationary in relation to the ground. If the plane is stationary in relation to the ground, then no significant air movement occurs over the wing, so no lift is generated.
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OP said:
Here's the original problem essentially as it was posed to us: "A plane is standing on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"
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Both you and the youtube poster have made an uncorrect assumption. You both assume that the conveyor can in some way hold the plane stationary. To suggest it is implied in the original question is purely your interpretation of the problem.

EDIT: Just re-read the YouTube post - does this guy realise that the outer surface of the earth rotates at 1000mph relative to a stationary point? ;)
 
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Meh - I hate silly questions.

We can't tell from the question whether it will or wont. Either are possible.

We don't know if the aircraft will move fast enough to reach take off speed as the wheels are not going to be friction free. You could forseably speed the conveyor belt up to the point that the wheels cease and the plane goes backwards!
 
I havnt read the whole thread. In short, this whole thing is total rubbish because the question given is COMPLETELY different to the question answered.

The answer to the question 'will it take off' is NO. No upwards thrust is created as there is no air movement over the wings.

The answer to the question 'If the conveyor moves in the opposite direction at the same speed as the plane, can the plane ever over come the backwards force to provide enough thrust to move fowards and take off as normal' is YES. Once friction is overcome, the plane requires no more thrust to remain stationary on the conveyor and is able to accelerate forwards.

I will reiterate though, whoever first proposed 'will it take off' is a total retard.
 
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