Think your smart?

WhiteStallionGT · May 27, 2006

I kinda take back my previous answer.

"The conveyor belt spins in reverse the exact same speed as the wheels at any given time"

So no matter how much thrust the airplane provides... the belt will match it. It's like trying to run up a set of escalators going the opposite direction. The faster you run, the faster it goes. It would be impossible to reach the top. So, the harder the engines work, the faster the belt goes, meaning the wheels will never get off the ground. It's like a plane taking off in a stationary position with it's engines at full blast. It's impossible. It needs to be in a state of motion.

Damnit stangnet, I had to use my brain and I'm on summer vacation.

HISSIN50 · May 27, 2006

Because of how this is worded, we assume the plane has no movement on the X-axis, correct? It matters not how power is delivered (wheels or jets) - if the wheel starts to turn, the treadmill negates the forward progress. So when an observer looks at it from the tower, there is no net horizontal displacement.

E.g., if a dude is on rollerskates and is on a this treadmill. I am standing on terra firma to the side of him and push his back to propogate forward movement - as soon as his little wheelies start to move, the treadmill goes the otherway and my pushing on his back does not make him change his absolute X-displacement.

I dont know much about airplane dynamics. There might be some Bernouli effect because of the turbulence caused by the plane's engine, though none from cutting the ambient air. I also dont know about the dynamic needed for take off - if the little bit of self-inflicted turbulence is enough to allow a slight lift, then with enough theoretical thrust/power, the plane could start to lift off, it would seem.

If we say it needs lift from cutting the air (via X-axis movement), I say it wont take off.

The horrible wording/phrasiology of the question (not by Stangster - I think it's intentionally ambiguous) makes it so that I kinda wonder if there is a correct answer - there is enough left open to interpretation.

Black95GTS · May 27, 2006

If the plane has no lateral movement, then it cannot lift off. The shape of the wing cutting through the air causes high pressure to form under the wing, and low pressure to form on top of it. The more force with which the wing is forced into the air, the more the pressure differential becomes, until enough "lift" is created to put the plane into the air.

The "stall speed" mentioned above is the minimum where the plain's wings aren't forced into the air enough to cause the necessary pressure differential.

If there is no lateral movement of the plane, then no pressure differential can exist, which means no lift can exist. The plane cannot take off.

Adam

OrangeMustangGt · May 27, 2006

i agree.....the plane WILL take off because the engines push the plane, and it will just take off normally as if there was no conveyer belt......the wills will just spin faster.

Now if this were a mustang, then no, the car wouldent move.

mo_dingo · May 27, 2006

HISSIN50 said:
Because of how this is worded, we assume the plane has no movement on the X-axis, correct? It matters not how power is delivered (wheels or jets) - if the wheel starts to turn, the treadmill negates the forward progress. So when an observer looks at it from the tower, there is no net horizontal displacement.

E.g., if a dude is on rollerskates and is on a this treadmill. I am standing on terra firma to the side of him and push his back to propogate forward movement - as soon as his little wheelies start to move, the treadmill goes the otherway and my pushing on his back does not make him change his absolute X-displacement.

I dont know much about airplane dynamics. There might be some Bernouli effect because of the turbulence caused by the plane's engine, though none from cutting the ambient air. I also dont know about the dynamic needed for take off - if the little bit of self-inflicted turbulence is enough to allow a slight lift, then with enough theoretical thrust/power, the plane could start to lift off, it would seem.

If we say it needs lift from cutting the air (via X-axis movement), I say it wont take off.

The horrible wording/phrasiology of the question (not by Stangster - I think it's intentionally ambiguous) makes it so that I kinda wonder if there is a correct answer - there is enough left open to interpretation.

I love this one. It always gets people.

I agree with you about the first part JT:

#1 - The plane must move as observed in relation to a fixed object off of the belt in order to create lift. With out the planes movement, it will not take off. You need air to flow underneath the planes wings to create lift. The planes speed creates this air flow, which allows take off. Period.

Here is where I disagree.

#2 - If the belt is spinning backwards, it will actually turn the planes wheels forward. If the belt spins forward, it will spin the tires backwards. A person on roller skates on a treadmill will move forward, not backward. Regardless, there is friction between the bearings on the roller skates, which will propell the skater forward, which means he will have to hold the side rails to stay in one place. Only if the bearings were somehow magically (frictionless), then the skater would remain stationary. The skaters weight multiplies the coefficient of static/dynamic friction present in the bearings.

i.e. If the static coefficient of each wheel was .09, then you would use the equation View attachment 466969

Where F = force due to friction, u = coefficient and N = the force normal to the contact surface. (normal means the amount of force applied perpendicular to the contact surface. Since gravity points straight down, in this case, the normal force is always the weight of the object that is on the bearings.

Which means the greater the weight of the object, the more force is applied to lateral movement.

#3 - Whatever way/speed the tires spin, it has little affect on the planes movement. It is attached to bearings, so the tires spin and the plane does not stay in the same spot on the belt. (Because the plane weighs as much as it does, the friction that exists on the bearings will apply a slight force to the plane's axles, and it may move, but not very much). IMO, I think the friction is too small overcome the plane's inertia.

#4 - The only reason a plane's wheels spin forward is because the ground/tire contact has friction, which makes the tires spin forward. And that only happens because the ground is stationary.

#5 - If the belt is moving forward (making tires spin backwards), The plane is still on bearings, and the axle inside the bearing which is mounted to the frame of the airplane does not turn. It only has a tiny amount of friction applied from the bearings, which the planes jet engines can easily overcome, thus the plane will still move forward, and take off.

I think the force of friction will still be very small compared to the force that the jet engines apply, thus it will be able to overcome the force friction applies, and the jet will take off. It will use more runway length to get up to speed, but that's the extent of it.
Scott

GRGT1994 · May 27, 2006

Wow Mo-Dingo, that's a great, detailed writeup.

This really is a simple question, and I think where people get tripped up is that they think the plane has it's wheels locked or something. Who cares which direction or how fast the tires are spinning. Put the thing on casters for all i care. The plane will still move FORWARD when the engines fire. Hence, forward motion, hence accelerating speed, hence life, hence flying.

Stangster5.0 · May 27, 2006

Answer!

Alot got this right to my suprise!Good job for those that said yes it can takeoff!

If you did this in a car,you would sit still because the force that propelles the car forward is being directly countered against by the conveyor,hence there is an equal energy exchange and no movement can occur.However,in a plane the force provided to move the mass forward is the energy created by the engine whether its a jet or a prop.The wheels have no barring on movement in this case cause they arent supplying the force or energy to move the plane.Although you have an equal exchange of energy from the wheels with the conveyor spinning the opposite direction,they are not applying the force to move forward.The plane will build enough speed to take-off,cause there is no opposing force to cancel the energy created by the engine!

In laymans terms.All that is gonna happen is the wheel speed will double(because its being countered against) as the plane is taking off.

Its really a common sense question,but I looked way to far into it the first time.Now onto this rope thing,LoL ,its jus to simple to be 26000miles + 10 feet.You just know there is something else to this.

super302 · May 27, 2006

you a member on ot.com??

Stangster5.0 · May 27, 2006

Nope.I got this outta a gaming clans forum that I belong too.TMX.It really stirred up a rucas in the forums.the answer was already posted,and people still go in and say its not possible,lmfao.It just trips me out.

http://www.clan-tmx.us/forums/index.php?act=idx
Youll have to join the forums to view the thread.

Its under intresting question in general discussion.

HISSIN50 · May 27, 2006

So is the plane still stagnant in terms of absolute X-axis movement? I interpreted the answer otherwise, but given the wording of the initial query, I dont see how any X-axis displacement occurs.

Stangster5.0 · May 27, 2006

Another exampleut a bike on a treadmill and turn the treadmill on.the treadmill goes one way,the bike wheel spins the opposite direction,no forward movement of the bike can occur.

Now,push the bike forward as if you were the planes engine applying thrust.What happens.

WhiteStallionGT · May 27, 2006

I'm such a moron.

HISSIN50 · May 27, 2006

Stangster5.0 said:
Another exampleut a bike on a treadmill and turn the treadmill on.the treadmill goes one way,the bike wheel spins the opposite direction,no forward movement of the bike can occur.

Now,push the bike forward as if you were the planes engine applying thrust.What happens.

Because the treadmill will run at the speed of the bike wheels (albeit in the opposite direction), the bike does not move forward no matter how hard or fast you push.

The original problem said that the treadmill matches the speed of the plane wheels, not that the treadmill was driven at some given speed (as I interpreted the example above).
Did I miss something?

The Green GT · May 27, 2006

I dont think it would take off. The bottom of the wing is curved and it takes the air longer to co across the bottom of the wing than it does over the top. Thats how the plane gets the lift it needs to take off, if its not actually moving and there is no wind, then there can be no lift.

BlueOvalStangGT · May 27, 2006

The Green GT said:
I dont think it would take off. The bottom of the wing is curved and it takes the air longer to co across the bottom of the wing than it does over the top. Thats how the plane gets the lift it needs to take off, if its not actually moving and there is no wind, then there can be no lift.

Thats an F1 spoiler, wings are the opposite with a curved top.

pleasehelp · May 28, 2006

The way I read it I thought you said that the belt would match the speed that the plane would normally move. Meaning it would stay stationary, therefore, it would not create any lift to take off.

Kinda like a stationary bike. No matter how hard you pedal it, you are not going anywhere.

HISSIN50 · May 28, 2006

pleasehelp said:
The way I read it I thought you said that the belt would match the speed that the plane would normally move. Meaning it would stay stationary, therefore, it would not create any lift to take off.

Kinda like a stationary bike. No matter how hard you pedal it, you are not going anywhere.

You and I read it the same way. The tires are connected to the conveyor (the plane isnt hovering) so any forward movement attempted by the plane is automatically negated by the conveyor. It matters not how the plane is propelled or how fast, the plane doesnt have any absolute X-axis displacement.

Therian · May 28, 2006

There's too many flaws with this riddle...

wouldn't the tires be completely shreaded? And the plan would collapse because of that? VTOL is the only way I can see the plane taking off. I understand that the friction of the wheels is basically unimportant compared to the power of the jet engines, but if there's no wheels at all, there's major problems.

yellow1995Cobra · May 28, 2006

HISSIN50 said:
Because the treadmill will run at the speed of the bike wheels (albeit in the opposite direction), the bike does not move forward no matter how hard or fast you push.

The original problem said that the treadmill matches the speed of the plane wheels, not that the treadmill was driven at some given speed (as I interpreted the example above).
Did I miss something?

I agree. If the treadmill is matching the bikes speed, then why would it matter if your pushing it or riding the bike? That bike is not going anywhere.

HISSIN50 · May 28, 2006

yellow1995Cobra said:
I agree. If the treadmill is matching the bikes speed, then why would it matter if your pushing it or riding the bike? That bike is not going anywhere.

This is how I interpreted it as well - any movement in these scenarios requires the wheel to move, and that motion is negated per the wording of the problem.

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