Originally posted by mwmillerSorry for the temporary absence but I had to go to work for a while.
What you said is:
"No, if the plane is moving at 5 kph to the left on the surface of the belt, relative to it and the belt is moving at the same speed. also to the left then the 2 speeds are additive in relation to a fixed observer - ie. 10 kp h to the left."
I disagree....
A fixed observer would see a plane moving at 5 kph to the left, and a belt ...[text shortened]... he plane moving in one direction at 5 kph and the belt moving in the other direction at 5 kph.
I just wanted to add that in your scenario, what you say would be true if we were talking about a car and a belt moving in the same direction.
In other words an observer at a fixed point would see a belt moving at 5 kph and a car moving at 10 kph since the car would be moving on the belt at 5 kph and the belt would be moving the car another 5 kph faster.
When you substitute a plane in place of the car, it is no longer true. The reason for this is that the car is pushing itself forward by applying force from its' wheels onto the surface of the belt, but the plane is not.
Yes, so taking the two possible scenarios.
1) Belt moving in opposite direction to plane at 5km/h, relative to stationary observer.
Plane moves forward at 5 km/h relative to stationary observer, and 10 km/h relative to belt i.e. the wheels are spinning at 10 km/h
The plane is NOT stationary as Sugiezd believes because no braking force is being applied to it.
2) Belt moving in same direction as plane at 5 km/h relative to stationary observer.
Plane still moves forward at 5 km/h but the wheels are motionless. Plane is stationary relative to belt.
You know what I think? I think that the people who disagree with the solution involving the plane taking off have the wrong idea about the problem. I think they're thinking "if the plane is stationary, and the conveyor belt starts moving, will the plane take off?" and of course, the answer is no...unless the pilot starts the engine.
I think people are trying to answer the question "will running a conveyor belt under the plane, turning the wheels in the process, result in lift? After all, the plane is now moving forward relative to the ground (belt)". In this case, the answer is no, the plane doesn't generate lift sitting on a treadmill. However, the problem is really asking "will running a conveyor belt under the plane, turning the wheels in the process, stop the plane from moving forward and creating lift?", in which case the answer is no, the plane can move forward just fine provided its engine is on and the brakes are off.
Just my (long-winded) two cents. Now let's never speak of this again...😵
The key to the whole thing is to understand how a plane works. If it moves, it is moving through the air. It's engine pulls or pushes it through the air.
It does not exert any force against the surface upon which it is setting in order to move. It rolls across the surface but that is all. The wheels allow it to roll with less friction but they are not exerting any force against the runway.
Originally posted by mwmillerNo, the key is to understand the concept of relative motion.
The key to the whole thing is to understand how a plane works. If it moves, it is moving through the air. It's engine pulls or pushes it through the air.
It does not exert any force against the surface upon which it is setting in order to move. It rolls across the surface but that is all. The wheels allow it to roll with less friction but they are not exerting any force against the runway.
When a problem is stated, as this one is, such that one object (whatever it may be) is in motion on a surface (whatever that may be), the parameters such as speed and direction of the object can only be considered relative to the surface.
Once you understand that, in this case, where the plane's motion is relative to the surface of the belt via its wheels then you can see that it doesn't matter if the wheels are driven or not as it is the rotational speed of the wheels which is important.
If this is the same as the speed of the belt in the opposite direction, there can be no net forward movement.
Originally posted by mwmillerNo, I'm NOT saying that. The plane's speed on the belt remains the same but the whole damned contaption is moving the other way.
So you're saying that the belt is reducing the speed of the plane?
I don't think so. The plane is not exerting force against the belt to move forward. It happens to be rolling on the belt, but it is pulling itself through the air to move forward.
Originally posted by Marsan1. Re-read my posts - I didn't say that.
Yes, so taking the two possible scenarios.
1) Belt moving in opposite direction to plane at 5km/h, relative to stationary observer.
Plane moves forward at 5 km/h relative to stationary observer, and 10 km/h relative to belt i.e. the wheels are spinning at 10 km/h
The plane is NOT stationary as Sugiezd believes because no braking force is being applied ...[text shortened]... es forward at 5 km/h but the wheels are motionless. Plane is stationary [b]relative to belt.[/b]
In your scenario (which has nothing to do with the original problem), the plane will move forwards because you are defining that it must:
"Plane moves forward at 5 km/h relative to stationary observer"
When you stipulate that, how could there be any other outcome.
Stick your finger in your ear and say "red" backwards.
2. What's your point?
Originally posted by sugiezdI do not see why you feel that relative motion between the plane and the surface upon which is is standing is important.
No, the key is to understand the concept of relative motion.
When a problem is stated, as this one is, such that one object (whatever it may be) is in motion on a surface (whatever that may be), the parameters such as speed and direction of the object can only be considered relative to the surface.
Once you understand that, in this case, where the plan ...[text shortened]... same as the speed of the belt in the opposite direction, there can be no net forward movement.
Does the fact that the plane moves forward have any physical impact on the surface? No.
Does the fact that the surface moves in the opposite direction have any physical impact on the plane? No.
If the movement of the plane and the movement of the surface have no physical impact on each other, why do you think relative motion between the two is important?
Originally posted by mwmillerBecause, if you accept that the relationship of speed is between the plane's wheels and the surface of the belt then, by definition in the problem, they must be the same but in opposite directions and thus the plane remains stationary to an outside observer.
I do not see why you feel that relative motion between the plane and the surface upon which is is standing is important.
Does the fact that the plane moves forward have any physical impact on the surface? No.
Does the fact that the surface moves in the opposite direction have any physical impact on the plane? No.
If the movement of the plane and ...[text shortened]... no physical impact on each other, why do you think relative motion between the two is important?
Let me introduce a completely different situation for a moment.
A plane and a car are setting on a solid runway, side by side.
The runway is extremely slick, to the point that there is no possibility of traction or friction on its' surface.
The plane and car start their engines and attempt to move forward.
Will either the plane or the car be able to move forward?
Originally posted by mwmillerThe plane will move, the car not.
Let me introduce a completely different situation for a moment.
A plane and a car are setting on a solid runway, side by side.
The runway is extremely slick, to the point that there is no possibility of traction or friction on its' surface.
The plane and car start their engines and attempt to move forward.
Will either the plane or the car be able to move forward?
Nice try, I can see where you're going and it doesn't work.
Carry on though.
Originally posted by sugiezdIf the plane will move, then it would be possible for it to move fast enough to take off or fly. The wheels and runway have no part in this. They are irrelevant. Same as in the original puzzler.
The plane will move, the car not.
Nice try, I can see where you're going and it doesn't work.
Carry on though.
Originally posted by mwmillerIt's nothing like the original problem.
If the plane will move, then it would be possible for it to move fast enough to take off or fly. The wheels and runway have no part in this. They are irrelevant. Same as in the original puzzler.
You have a plane on a stationary runway (albeit slippery) - a different question entirely. You're scratching.
Originally posted by sugiezdTrue, it is different except for one point, which is the only one that is important.
It's nothing like the original problem.
You have a plane on a stationary runway (albeit slippery) - a different question entirely. You're scratching.
The plane moves forward, which means that it will take off or fly if it moves fast enough. Causing the runway to move in the opposite direction will not change what that plane is doing.
I don't know how to make it any more understandable.
The only thing the plane has in common with the surface is that it is touching it. The fact that the plane is moving is completely accomplished by the plane and its' engine (and the air through which it is moving). Nothing else is causing this plane to move, and nothing the surface does will alter that movement.