Ok people.
It is stated that the wheels and belt roll at the same speed in opposite directions.
Let's say the plane needs an air speed of 100m/s to take flight.
And let's say that the belt is moving at a fixed rate of 1000m/s. (which it is not)
Now, the plane's wheels on a normal runway would need to roll at 100m/s.
If we want to know how fast the wheels spin to take off from the belt, we just add normal wheel speed to belt speed. 100m/s + 1000m/s = 1100m/s.
Ah, but herein lies the rub: The wheels are now rolling faster than the belt!
It does not matter what air speed is required, so long as it is greater than zero, the plane can get nowhere.
Sorry, no go.
Max
It is stated that the wheels and belt roll at the same speed in opposite directions.
Let's say the plane needs an air speed of 100m/s to take flight.
And let's say that the belt is moving at a fixed rate of 1000m/s. (which it is not)
Now, the plane's wheels on a normal runway would need to roll at 100m/s.
If we want to know how fast the wheels spin to take off from the belt, we just add normal wheel speed to belt speed. 100m/s + 1000m/s = 1100m/s.
Ah, but herein lies the rub: The wheels are now rolling faster than the belt!
It does not matter what air speed is required, so long as it is greater than zero, the plane can get nowhere.
Sorry, no go.
Max
The problem with taking the belt as the point of reference is that the air must couple with it.
Max
Max
Tony, very observant.
I just looked for something that worked, without involving flames. The question is formed where several interpretations are possible. It seems as valid as any other. But the question asked was : does the plane take off or not? Not an option was: does it burn, explode or break?
So I felt it was important to have only two answers. Heck, I could be totally wrong too.
Has anyone seen that poor guy with a rocket on his back?
-Chris
I just looked for something that worked, without involving flames. The question is formed where several interpretations are possible. It seems as valid as any other. But the question asked was : does the plane take off or not? Not an option was: does it burn, explode or break?
So I felt it was important to have only two answers. Heck, I could be totally wrong too.
Has anyone seen that poor guy with a rocket on his back?
-Chris
Hi Max,
Hitch Hikers Guide to the Universe. 42 was the answer to the question of life, the universe and everything.
You've never seen or read it? BBC production, satire on bureaucracy. Arthur Dent was a character .... awwwwh forget it.
-Chris
Hitch Hikers Guide to the Universe. 42 was the answer to the question of life, the universe and everything.
You've never seen or read it? BBC production, satire on bureaucracy. Arthur Dent was a character .... awwwwh forget it.
-Chris
Hi Max,
Now the air. It just sits there in a mass. More related to the earth than a little belt whipping about.
-Chris
Now the air. It just sits there in a mass. More related to the earth than a little belt whipping about.
-Chris
Hi Max,
Thanks, actually I did miss your reference. Sorry mate!
So is the towel near your feet or head?
-Chris
Thanks, actually I did miss your reference. Sorry mate!
So is the towel near your feet or head?
-Chris
anatech said:
Mine's hanging over the shower curtain rod. I guess nearer my head than my feet.
It's 7:36. Do you know where your towel is?
Max
maxro said:
OK
OK again
I agree
No the wheels and belt are turning at the same speed. The plane is moving over the surface of the belt at an ever increasing rate and the belt is reacting by accelerating at the same time with zero lag. I think I understand your dilemma in that if motion is created over the surface of the belt (the plane has moved from the beginning of the belt to the end) at then by golly the wheels have to be turning faster than the belt or there would be no forward motion. But if you forget that the motion that you think you are seeing is there because you have a flat surface and therefore an easily identifiable reference point on the belt and not on the wheel then you fail to see the forward (or backward) movement in the wheel structure. It's just easier to see on the flat belt. That's why you think you are seeing forward movement over the belt surface. You are not you just can't see the same thing on a round wheel
Yes go.
EDIT:
If I misunderstand your thoughts, please forgive.
maxro said:
yeah so some wind will be blowing past no big deal..... the whole thing with points of reference is that motion is relative to whatever you make your point of reference. The ground you are standing on isn't moving (unless there is an earthquake or something) from the reference point of your eyes, however if you now go out into space and look at where you were standing on the earth (with a very powerfull telescope 😉 ) then from that reference point the ground is actually moving and so were you.
Because the question doesn't stipulate the point of reference you are free to make it whatever you want, we just always think of things from our own point of reference, ie our own eyes. Have you ever been sitting in a car or bus stopped beside another vehicle, suddenly you feel like your car/bus is moving forward, but in reality it is the other vehicle that is moving backwards 🙂 we associate (when we are in a vehichle) forward movement as being the surroundings moving away from us, and our brain can be fooled into thinking we are moving forward when we aren't.
Tony.
Okay,
Just a question. How do you interpret this line?
I'm not making a point. I just want to know since this appears to be the sticking point. Forget everything else, just this.
-Chris
Just a question. How do you interpret this line?
I'm not making a point. I just want to know since this appears to be the sticking point. Forget everything else, just this.
-Chris
My initial interpreation of this was that the speed of the conveyor was such that whatever speed the wheel was turning the speed of the conveyor was matched in such a way as the wheel stays stationary with respect to a point of reference away from either the belt or the wheel (ie on the ground outside of the belt).
edit: on a side note what does matched mean!!!!!!!
edit: on a side note what does matched mean!!!!!!!
Cal Weldon said:
Man, that was a confusing read.
let's reiterate:
-wheels, which have no driving force of their own, are attached to the plane by axles at their centres.
-belt rides on rollers, around axles, which are attached to the earth.
-belt is as long as a runway (completely unimportant, Plane could be rolling on a drum for all we care)
-surface speed of wheels and belt are equal but opposite at all times (in reference to the stationary earth)
-plane has an engine that exerts a force which tends to pull it forward.
-plane needs forward movement relative to the earth to fly.
We must take the earth as our point of reference:
For the plane to make progress (relative to the air/earth), its wheels must roll forwards FASTER (in relation to the earth) than the belt is rolling backwards (in relation to the earth).
This is simply not allowed.
Max
anatech said:
Just saying that the fact the plane has moved from the beginning of the belt to the end doen't mean the wheels are moving faster than the belt. Just that the plane which is independant of the wheel movement has changed it's position on the belt...
...in a long, drawn out, confusing Cal style, that's all. 😉
Ok, lets put a speedometer on the plane's wheels.
This would measure the wheel speed relative to the plane.
And, let's put a speedometer on the belt.
This would measure the belt's speed relative to the earth.
The only way that these two speedos read the same is if the plane and earth are not moving with respect to one another.
Max
This would measure the wheel speed relative to the plane.
And, let's put a speedometer on the belt.
This would measure the belt's speed relative to the earth.
The only way that these two speedos read the same is if the plane and earth are not moving with respect to one another.
Max
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