The Cellar  

Go Back   The Cellar > Main > Home Base

Home Base A starting point, and place for threads don't seem to belong anywhere else

Reply
 
Thread Tools Display Modes
Old 12-07-2006, 11:34 AM   #1
Kitsune
still eats dirt
 
Join Date: Sep 2003
Location: Tampa, FL
Posts: 3,031
The "Plane on a Treadmill" Question

The riddle/question is on every other forum. I figure I should bring the torture here, as well.

A plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, it moves backwards beneath the aircraft.

As the engines throttle up, does the plane take off?
Kitsune is offline   Reply With Quote
Old 12-07-2006, 11:36 AM   #2
Undertoad
Radical Centrist
 
Join Date: Jan 2001
Location: Cottage of Prussia
Posts: 31,423
I've never heard this before. But no, a plane takes off because its wings generate lift, which it can only do when moving forward.
Undertoad is offline   Reply With Quote
Old 12-07-2006, 11:37 AM   #3
Kitsune
still eats dirt
 
Join Date: Sep 2003
Location: Tampa, FL
Posts: 3,031
Why would the plane not move forward?
Kitsune is offline   Reply With Quote
Old 12-07-2006, 11:39 AM   #4
barefoot serpent
go ahead, abbrev. it
 
Join Date: Jun 2005
Location: Lawrence, KS
Posts: 2,623
no, unless the engine thrust > wt. of plane... but that's a lot of thrust for your average puddle jumper.

edit: the Harrier could 'jump' off a moving runway
__________________
Chooses rowing vs. wading

Last edited by barefoot serpent; 12-07-2006 at 11:50 AM.
barefoot serpent is offline   Reply With Quote
Old 12-07-2006, 11:44 AM   #5
glatt
 
Join Date: Jul 2003
Location: Arlington, VA
Posts: 27,717
The engines of the plane push against the air, so the runway doesn't matter. The wheels will rotate as much as they have to as the plane pushes against the air. The runway is not relevant once the plane's engines start.
glatt is offline   Reply With Quote
Old 12-07-2006, 11:50 AM   #6
Flint
Snowflake
 
Join Date: Mar 2006
Location: Dystopia
Posts: 13,136
No.

.
__________________
******************
There's a level of facility that everyone needs to accomplish, and from there
it's a matter of deciding for yourself how important ultra-facility is to your
expression. ... I found, like Joseph Campbell said, if you just follow whatever
gives you a little joy or excitement or awe, then you're on the right track.

. . . . . . . . . . . . . . . . . . . . . . . . . . Terry Bozzio
Flint is offline   Reply With Quote
Old 12-07-2006, 11:52 AM   #7
glatt
 
Join Date: Jul 2003
Location: Arlington, VA
Posts: 27,717
Yes, damnit!
glatt is offline   Reply With Quote
Old 12-07-2006, 11:55 AM   #8
Flint
Snowflake
 
Join Date: Mar 2006
Location: Dystopia
Posts: 13,136
No. No lift, as UT said. Planes do not take off from a stationary position. What would you expect it to do, suddently leap in the air? At what speed? From zero to what, in how many seconds? Same question: if you drop a paper airplane on the ground, will it suddenly leap in to the air and fly for no apparent reason? Same answer: No. The end.
__________________
******************
There's a level of facility that everyone needs to accomplish, and from there
it's a matter of deciding for yourself how important ultra-facility is to your
expression. ... I found, like Joseph Campbell said, if you just follow whatever
gives you a little joy or excitement or awe, then you're on the right track.

. . . . . . . . . . . . . . . . . . . . . . . . . . Terry Bozzio
Flint is offline   Reply With Quote
Old 12-07-2006, 11:57 AM   #9
Undertoad
Radical Centrist
 
Join Date: Jan 2001
Location: Cottage of Prussia
Posts: 31,423
The plane will move forward but not enough to gain enough lift. The wheels on the ground fight the force of gravity, until the plane has enough forward momentum for the wings to produce lift. Now the wheels are not fighting the force of gravity as hard so the engines have to fight it harder. That's my story and I'm stickin to it, until someone posts something that makes it look bad.
Undertoad is offline   Reply With Quote
Old 12-07-2006, 11:58 AM   #10
Kitsune
still eats dirt
 
Join Date: Sep 2003
Location: Tampa, FL
Posts: 3,031
Quote:
Originally Posted by Undertoad
The plane will move forward but not enough to gain enough lift. The wheels on the ground fight the force of gravity, until the plane has enough forward momentum for the wings to produce lift. Now the wheels are not fighting the force of gravity as hard so the engines have to fight it harder. That's my story and I'm stickin to it, until someone posts something that makes it look bad.
The friction of the wheels in this question and, even in the real world, is pretty much of no consequence. The engines, being as powerful as they are, should easily be able to overcome it.

Hearing people explain this question and their answer has made me drop this into my "interview pool", alongside the "explain why manhole covers are round" question. I love it.
Kitsune is offline   Reply With Quote
Old 12-07-2006, 11:59 AM   #11
glatt
 
Join Date: Jul 2003
Location: Arlington, VA
Posts: 27,717
Of course there is lift. The plane will move forward against the air, and twice as fast against the runway. It will take off just like it normally would. A plane's wheels are not powered. They spin freely as the engines push against the air. The air is stationary, only the runway is moving.
glatt is offline   Reply With Quote
Old 12-07-2006, 11:59 AM   #12
Flint
Snowflake
 
Join Date: Mar 2006
Location: Dystopia
Posts: 13,136
No! The engines (normally) move the plane forward to make air go across the wings and produce lift. No going forward, no lift, no take off.
__________________
******************
There's a level of facility that everyone needs to accomplish, and from there
it's a matter of deciding for yourself how important ultra-facility is to your
expression. ... I found, like Joseph Campbell said, if you just follow whatever
gives you a little joy or excitement or awe, then you're on the right track.

. . . . . . . . . . . . . . . . . . . . . . . . . . Terry Bozzio
Flint is offline   Reply With Quote
Old 12-07-2006, 12:01 PM   #13
dar512
dar512 is now Pete Zicato
 
Join Date: May 2003
Location: Chicago suburb
Posts: 4,968
If it were a car and depended on the friction between the tires and the ground to move forward, that would be another thing. But in this case, the backward thrust of the engine is what's moving the plane forward. I don't think the treadmill would have much of an effect on the outcome, if any.

Think of it this way. A plane already in the air flies just over the treadmill. Does the movement of the treadmill affect the movement of the plane?
__________________
"Against stupidity the gods themselves contend in vain."
-- Friedrich Schiller
dar512 is offline   Reply With Quote
Old 12-07-2006, 12:02 PM   #14
Flint
Snowflake
 
Join Date: Mar 2006
Location: Dystopia
Posts: 13,136
It's not already in the air, and it will never get there from a staionary position. The engines DO NOT "push" the plane into the air.
__________________
******************
There's a level of facility that everyone needs to accomplish, and from there
it's a matter of deciding for yourself how important ultra-facility is to your
expression. ... I found, like Joseph Campbell said, if you just follow whatever
gives you a little joy or excitement or awe, then you're on the right track.

. . . . . . . . . . . . . . . . . . . . . . . . . . Terry Bozzio
Flint is offline   Reply With Quote
Old 12-07-2006, 12:03 PM   #15
Kitsune
still eats dirt
 
Join Date: Sep 2003
Location: Tampa, FL
Posts: 3,031
Quote:
Originally Posted by Flint
It's not already in the air, and it will never get there from a staionary position. The engines DO NOT "push" the plane into the air.
Sure they do. What, you think the wheels do it?
Kitsune is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT -5. The time now is 04:02 AM.


Powered by: vBulletin Version 3.8.1
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.