Physics question - Page 3 - Subaru Enthusiasts Car Club of the Sierras

sperry · 2005-11-28, 04:53 PM

Quote:

Originally Posted by JC

It means the plane can never move. Draw a diagram Mike and explain to me how you are moving without sliding or having the wheels be different speeds. Both my friend and I got this pretty fast guys, he even laughed when he read it. C'mon now, always read the problem before you start doing it. And quit your bitchin' Scott.

JC, I'll stop bitching when you draw me the force diagram that shows the equal and opposite force to the engine thrust that prevents the plane from moving.

Dean · 2005-11-28, 04:54 PM

Wish I had seen this earlier...

The question is a paradox and has no solution. Theere are two physical systems that are both mutually dependent, and dicontinious at the same timee that generate conditions that mutual exclusive.

The first system is the wings, and airspeed. This combination is the only thing that can lift the plane.

The second system is a belt and planes wheels. "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation."

Since the plane is at rest to begin with "is sat on the beginning of a massive conveyor belt" Wheel speed is zero, and since there is no force directly applied to the wheels, they can never spin since "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation" -0 +0 = 0 . The wheels can never turn. There are no provisions in the premis for the conveyor belt to move for any other reason, other than the wheels rotating, so it can never turn. This is the limiting factor in the wheel/conveyor belt system.

The plane of course though can thrust all it wants, and that force should cause motoin, airspeed, and eventually lift. But the tires/conveyor belt cannot turn/move, so neither can the plane.

Paradox...

Go hop in your time machine and kill your grandfather before your father was born if you don't beleive me.

sperry · 2005-11-28, 05:02 PM

Quote:

Originally Posted by sperry

JC, I'll stop bitching when you draw me the force diagram that shows the equal and opposite force to the engine thrust that prevents the plane from moving.

Here I took care of it for you:

cody · 2005-11-28, 05:04 PM

The plane isn't a Harrier by chance is it?

cody · 2005-11-28, 05:06 PM

And the plane can take off if there is a headwind greater than or equal to it's takeoff speed.

MikeK · 2005-11-28, 05:06 PM

Quote:

Originally Posted by JC

It means the plane can never move. Draw a diagram Mike and explain to me how you are moving without sliding or having the wheels be different speeds. Both my friend and I got this pretty fast guys, he even laughed when he read it. C'mon now, always read the problem before you start doing it. And quit your bitchin' Scott.

The only thing I can possibly think of that you are trying to say is that this:

"exactly match the speed of the wheels"

... doesn't refer to the speed of the surface of the wheel/conveyor belt, but the rotational speed. Is this correct?

(It doesn't matter anyway, my plane has huge wheels, their circumference is the same as the circumference of the conveyor belt, so it can still take off!)

MikeK · 2005-11-28, 05:07 PM

Quote:

Originally Posted by cody

And the plane can take off if there is a headwind greater than or equal to it's takeoff speed.

you mean headwind + groundspeed (also known as airspeed)

Dean · 2005-11-28, 05:08 PM

Quote:

Originally Posted by cody

The plane isn't a Harrier by chance is it?

Cody Wins... A VTOL is the only type of plane that makes this a non-paradox.

ScottyS · 2005-11-28, 05:08 PM

Quote:

The problem *is* poorly posed.

Yah, and I'm glad I got here late...

JC · 2005-11-28, 05:09 PM

Quote:

Originally Posted by sperry

Here I took care of it for you:

lmao, see now you get it. Nice balance on that plane there, sitting on one wheel and all.

Yes Mike, rotational speed. No one measures wheel speed as the speed of the aircraft with respect to the ground. It doesn't matter how big your belt is.

cody · 2005-11-28, 05:12 PM

Quote:

Originally Posted by MikeK

you mean headwind + groundspeed (also known as airspeed)

Huh? Well there is no groundspeed, but yah, I guess. I know jack about airplanes.

cody · 2005-11-28, 05:13 PM

Quote:

Originally Posted by Dean

Cody Wins... A VTOL is the only type of plane that makes this a non-paradox.

Sweet, I knew all that late night GTA Vice City would pay off someday.

MikeK · 2005-11-28, 05:15 PM

Quote:

Originally Posted by JC

It doesn't matter how big your belt is.

Says an american ... ZING!

Actually if the belt and the wheels are the same circumference then they can rotate at the same speed without sliding. Here is a scale diagram to show what I mean:

cody · 2005-11-28, 05:17 PM

The size of the wheels doesn't matter.

JC · 2005-11-28, 05:19 PM

Quote:

Originally Posted by MikeK

Says an american ... ZING!

Actually if the belt and the wheels are the same circumference then they can rotate at the same speed without sliding. Here is a scale diagram to show what I mean:

Ya but you would still be sitting in one place.

MattR · 2005-11-28, 05:25 PM

Quote:

Originally Posted by JC

Nice balance on that plane there, sitting on one wheel and all.

OMG, you are such an ass...hahahaha...That killed me.

Nick Koan · 2005-11-28, 06:12 PM

Quote:

Originally Posted by cody

The size of the wheels doesn't matter.

You're right. Its the motion of the ocean.

JC · 2005-11-28, 06:47 PM

Quote:

Originally Posted by nKoan

You're right. Its the motion of the ocean.

That's just what girls say when the only thing they can stroke without laughing is your ego.

Pat R. · 2005-11-28, 07:48 PM

Here's the seven page C-C.com thread on the subject.

sp00ln · 2005-11-28, 07:52 PM

JC,

How can a harrier take off then? It too essentially has a frictionless bottem.

cody · 2005-11-28, 07:56 PM

The reason, in my mind, a harrier can take off is that it requires zero latteral motion and therfore doesn't need the landing gear wheels to roll. This is also the reason I said a normal airplane can take off if the headwind is equal to or greater than the [airspeed] the plane requires to lift off.

JC · 2005-11-28, 08:03 PM

Quote:

Originally Posted by sp00ln

JC,

How can a harrier take off then? It too essentially has a frictionless bottem.

Same reason a rocket does, lots of vertical thrust.

sperry · 2005-11-28, 08:11 PM

Quote:

Originally Posted by Pat R.

Here's the seven page C-C.com thread on the subject.

The version of the question in that thread is the correct version that actually does have a solution.

M3n2c3 · 2005-11-28, 08:14 PM

NASIOC = 16 pages
SECCS = 3 pages

hmmm. . .

JC · 2005-11-28, 08:21 PM

Quote:

Originally Posted by M3n2c3

NASIOC = 16 pages
SECCS = 3 pages

hmmm. . .

Ya well half of us are engineers and one of us is an airplane designer.

2005-11-28, 04:54 PM	#52
Dean Señor Cheap Bastarde Real Name: Dean Join Date: May 2003 Location: $99 Tire Store Posts: 9,294 Car: $.04 STI Class: Fast,Cheap & Reliable=STI Deal, did somebody say Deal? Oh, Dean, yeah that's me.	Wish I had seen this earlier... The question is a paradox and has no solution. Theere are two physical systems that are both mutually dependent, and dicontinious at the same timee that generate conditions that mutual exclusive. The first system is the wings, and airspeed. This combination is the only thing that can lift the plane. The second system is a belt and planes wheels. "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." Since the plane is at rest to begin with "is sat on the beginning of a massive conveyor belt" Wheel speed is zero, and since there is no force directly applied to the wheels, they can never spin since "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation" -0 +0 = 0 . The wheels can never turn. There are no provisions in the premis for the conveyor belt to move for any other reason, other than the wheels rotating, so it can never turn. This is the limiting factor in the wheel/conveyor belt system. The plane of course though can thrust all it wants, and that force should cause motoin, airspeed, and eventually lift. But the tires/conveyor belt cannot turn/move, so neither can the plane. Paradox... Go hop in your time machine and kill your grandfather before your father was born if you don't beleive me. __________________ I am a Commodore PET --- Now get off my lawn you kids... Last edited by Dean; 2005-11-28 at 04:57 PM.

2005-11-28, 05:04 PM	#54
cody Candy Mountain Real Name: Cody Join Date: May 2005 Location: Californication Posts: 7,751 Car: 03 Pussy Wagon, now with more pink! Class: TESP OMG Internet!	The plane isn't a Harrier by chance is it? __________________ Slow and low, that is the tempo.

2005-11-28, 05:06 PM	#55
cody Candy Mountain Real Name: Cody Join Date: May 2005 Location: Californication Posts: 7,751 Car: 03 Pussy Wagon, now with more pink! Class: TESP OMG Internet!	And the plane can take off if there is a headwind greater than or equal to it's takeoff speed. __________________ Slow and low, that is the tempo.

2005-11-28, 05:17 PM	#64
cody Candy Mountain Real Name: Cody Join Date: May 2005 Location: Californication Posts: 7,751 Car: 03 Pussy Wagon, now with more pink! Class: TESP OMG Internet!	The size of the wheels doesn't matter. __________________ Slow and low, that is the tempo.

2005-11-28, 07:52 PM	#70
sp00ln EJ205 Join Date: May 2003 Location: Reno, NV Posts: 1,196	JC, How can a harrier take off then? It too essentially has a frictionless bottem. __________________ Turbo is a decent with modification.

2005-11-28, 07:48 PM	#69
Pat R. EJ251 Join Date: Feb 2004 Location: Southeast Hades Posts: 593 Car: Red Class: Stockish ¿Quién es tu padre?	Here's the seven page C-C.com thread on the subject.

2005-11-28, 07:56 PM	#71
cody Candy Mountain Real Name: Cody Join Date: May 2005 Location: Californication Posts: 7,751 Car: 03 Pussy Wagon, now with more pink! Class: TESP OMG Internet!	The reason, in my mind, a harrier can take off is that it requires zero latteral motion and therfore doesn't need the landing gear wheels to roll. This is also the reason I said a normal airplane can take off if the headwind is equal to or greater than the [airspeed] the plane requires to lift off. __________________ Slow and low, that is the tempo.

2005-11-28, 08:14 PM	#74
M3n2c3 EJ205 Real Name: Jeremiah Join Date: Jul 2005 Location: Lubbock, TX Posts: 1,888 Car: Current: 2014 Forester 2.5i Premium. Old: 2005 Impreza 2.5RS, 2000 Forester L Class: RNP, long ago (see motto) "Kids are ruining autocross."	NASIOC = 16 pages SECCS = 3 pages hmmm. . . __________________ Small red text that looks curious at first glance but is ultimately inconsequential

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