A plane on a runway, how smart is r3vlimited?

[Fidhle007]

Word. You can listen to my technical advice, although I rarely give it. I usually differ to the older, and more experienced members but this poll has given me a lot more confidence in my technical knowledge.

[Justin B]

62. i voted no originally, then saw the "duh" in it. :P

[Fidhle007]

62. i voted no originally, then saw the "duh" in it. :P

Actually, I did the same thing but I wasn't going to tell anyone. ;) About five seconds after voting I felt suddenly VERY stupid...

[matt]

It's a really good example of why frames of reference are so important in physics.

[equate975]

I took and passed a basic physics class with an A. What's funny is that my dad, who never took physics or went to college, immediately understood that since the wheels on an airplane are freewheeling, it doesn't matter how fast the treadmill spins in the opposite direction, that they will just spin and the plane will move foward by the thrust of the plane's propeller or jet. My brother, who is college educated, was fooled by the question, but eventually got it after I explained it to him - the first time.

It doesn't matter how big the wheels air. Take a plane and put some larger diameter wheels on it, being sure to maintain the weight and ground contact area, and it will have no effect on how well the plane can take off. A larger wheel will spin slower, that's all. Put it on the treadmill, and it will just spin twice as fast. It does not act like a gear. If we were talking about a car where the wheels supply the forward motion, then the wheels would act like a gear and affect its rate of movement.

I suppose a larger diameter wheel may require more energy to overcome the increased inertia, but being that the weight of the wheel has not changed, I'm not sure.

The only difference bigger (or smaller) wheels would play would be the same difference they would play on a normal runway. If the plane had 18 foot tall wheels and could still take off on a runway, it would still take off on the belt.

[Justin B]

Yay, we're getting it, or just forcing the naysayers out lol

Now the trick is to see how long the thead can go while trying to sound honest not knowing why it will take off, with all sorts of other ideas? What about the pull of the moon!?!??! :P :wgaf: :p

Well, on second thought how about no...

[benDASHDASH]

Yay, we're getting it, or just forcing the naysayers out lol

Now the trick is to see how long the thead can go while trying to sound honest not knowing why it will take off, with all sorts of other ideas? What about the pull of the moon!?!??! :P :wgaf: :p

Well, on second thought how about no...

justin, you are on to something. if the moon can pull the ocean's tides, weighing millions of tons, im sure it can at least overcome the planes downward force on the belt. this would cause enough slip of the wheels to allow the jets to propel the plane past the moving belt, allowing for a takeoff. looks like we won't have to test this after all. how can i revote?

[Jand3rson]

who is on the plane?

Samuel L. Jackson.

[Macktheknife]

Oh Ben, lol :)

First of all the plane is not powered like a car, it does not get the drive from its wheels, it gets it from a jet engine creating force through the air not through contact with the ground. The jets will push it through the air.

Here's how it will work really easy like, we'll assume there is no resistance at all on the wheels, even though there is, it is negligible and will not cause the plane to stay stationary.

We'll separate the accelerations of the plane and the roller underneath to make it really simple.

1) Conveyor belt starts turning backwards at 100mph, since the plane has no drag on the wheels it stays stationary. The planes wheels however, are spinning at 100mph to keep the plane stationary. As far as they are concerned, the plane is traveling at 100mph.

2) Plane accelerates to 100mph instantly (for sake of the example), now, the plane is going fast enough to lift off, and the wheels are now going at 200mph to keep up with the plane, and the belt spinning backwards. Really though as far as airflow over the wings though is concerned, and in reality, the plane is only traveling 100mph.

Now, the questions requirements are satisfied, the conveyor belt is going as fast as the plane is, and the plane may lift off.

If you want to get technical and throw in wheel drag in there, take two examples-

1) The plane on a normal runway will have a certain amount of drag from its wheel to reach and maintain 100mph. Great.

2) The plane on the conveyor belt will need to use a little bit more thrust, andwill need to accelerate for a slightly longer period of time to reach 100mph ground speed. Ground speed, meaning speed of things to the side of the belt, the rest of the world. The wheels are spinning at 200mph, its a miniscule amount of extra drag, but its there, but possible to overcome.



I'm going to dinner. I'll be right back :) At least I am getting in a lot of typing.

you are very correct, despite what the heathens say :)

The wheels serve to isolate the system (the plane). Now, if we cna assume a gigantic runway length conveyor belt exists, I'm gonna assume we can invent frictionless wheel bearings. Therefore, the conveyor belt can move at ANY speed and (when the small amount of friction in the wheel bearings is discounted) there will be NO external force acting on the plane. When the engines spool up, it will move forward and take off. It's EXACTLY the same principle as taking off on a runway of ice, or water. Planes do it all the time. You're taking off on a near-frictionless surface, and that boundary only serves to isolate the system.

Draw a free-body diagram if you've had any physics training, it helps a lot. It's a confusing question because when you think about it the fact that the conveyor belt moves at all is just extraneous information that has no bearing on the plane.

[H&Re30]

https://www.straightdope.com/columns/060203.html

[benDASHDASH]

the belt cannot out accelerate the plane

[M42Technik]

Alright, who bumped this shit!?!!?

Insta-ban.

[LINUS]

Alright, who bumped this shit!?!!?

Insta-ban.

Bingo. Time to go hunting with the ban stick. Strangely enough, it wasn't 242144214 6786969566 54654 's fault.