Mythbusters punk'd whole internet

[Cerpin Taxt]

Originally posted by: smack Down

Question for you two: What if we assume that the wheels are connected to the axles by perfectly frictionless bearings? Can the conveyor retard the airplane's forward movement then?

Yes of course it can. If you wish to see that for yourself go get a wheel and put it on a treadmill. Turn on the treadmill and watch the wheel come back at you. Use a wheel with no axle ans you will have almost frictionless bearings.

How exactly would the treadmill deliver the energy to the axle in order to propel it backwards?

 

[jmmtn4aj]

Originally posted by: smack Down

Originally posted by: her209

Originally posted by: smack Down

Originally posted by: Cerpin Taxt
Question for you two: What if we assume that the wheels are connected to the axles by perfectly frictionless bearings? Can the conveyor retard the airplane's forward movement then?

Yes of course it can. If you wish to see that for yourself go get a wheel and put it on a treadmill. Turn on the treadmill and watch the wheel come back at you. Use a wheel with no axle ans you will have almost frictionless bearings.

Thank you for proving to us you have no idea what you are talking about.

So you think if I put a wheel on a treadmill it will just stay put?

Good god man, an undercarriage with frictionless bearings does NOT equal an unattached wheel! Jesus!

What happens to the forward force exerted on the wheel by the axle? Remove the axle and the force is gone, obviously.

Isn't this high school level physics?

 

[Cabages]

I should have really asked my professor this...

It takes off!

Why is everyone so concerned with the wheels? (real question)

 

[Boo025]

I'm surprised this is still going.

 

[The Boston Dangler]

i still don't get why people think the plane's speed relative to the ground matters.

 

[jmmtn4aj]

Yeah, it's the messiest physics lesson ever..

To sum it all up;

While the wheels in a car exist both to support it and transfer energy to the ground in order to propel the car forwards, a plane's wheels only exist to support it. Planes don't generate thrust via contact with the ground.

Frictional force created by rotation of the wheels does oppose motion in whichever direction, but it isn't nearly enough to stop it from accelerating to take off speed. Structural failure would occur long before rotational speed is anywhere near the value required to create substantial friction.

If you want to stop a plane from taking off, don't bother with a treadmill. Give it shit load of tailwind. Tailwind matching the speed fo the aircraft ensures no lift is generated by airflow around the lift surface (read, wing), and the engines would probably stall. If you want to stop a plane relative to the ground, still don't bother with a treadmill. Instead, chuck something big and hard into the fan blades.

 

[Cerpin Taxt]

Originally posted by: Cabages

Why is everyone so concerned with the wheels? (real question)

Originally posted by: The Boston Dangler
i still don't get why people think the plane's speed relative to the ground matters.

There are essentially two ways to interpret the problem, and it concerns which rate of which object determines the rate of the conveyor belt. In one interpretation, the conveyor belt matches the speed of the plane's fuselage with respect to the ground. In another interpretation, the conveyor belt matches the speed of the angular rotation of the wheels.

Certain people seem to think that the latter interpretation is the more accurate interpretation. These also seem to be the only people left arguing that the plane does not take off, even though the only basis for such an argument involves absolutely ridiculous assumptions about the capacity of the conveyor belt to accelerate its surface sufficiently to magnify the second-order effects of the ordinarily-negligible friction between the bearings in the wheels and the axle and retard the forward motion of the plane such that it could not take off.

Except for smack Down, who seems to think that the angular momentum of a rotating wheel could somehow be magically transferred to an axle through frictionless bearings. He obviously lives in his own special reality.

 

[Tweak155]

Originally posted by: Cerpin Taxt

Originally posted by: Cabages

Why is everyone so concerned with the wheels? (real question)

Originally posted by: The Boston Dangler
i still don't get why people think the plane's speed relative to the ground matters.

There are essentially two ways to interpret the problem, and it concerns which rate of which object determines the rate of the conveyor belt. In one interpretation, the conveyor belt matches the speed of the plane's fuselage with respect to the ground. In another interpretation, the conveyor belt matches the speed of the angular rotation of the wheels.

Certain people seem to think that the latter interpretation is the more accurate interpretation. These also seem to be the only people left arguing that the plane does not take off, even though the only basis for such an argument involves absolutely ridiculous assumptions about the capacity of the conveyor belt to accelerate its surface sufficiently to magnify the second-order effects of the ordinarily-negligible friction between the bearings in the wheels and the axle and retard the forward motion of the plane such that it could not take off.

Except for smack Down, who seems to think that the angular momentum of a rotating wheel could somehow be magically transferred to an axle through frictionless bearings. He obviously lives in his own special reality.

Agreed. What they would need to realize is that with frictionless bearings, even with the airplane's engine turned off, the airplane would be at a near stand still even with the conveyor belt moving.

I say near stand still because its logical we could never create that perfect of a system, but assuming we had frictionless bearings, I don't think the plane could ever sit still because then it would have nothing (no friction/force) holding it in one place.

 

[Throckmorton]

Originally posted by: Cerpin Taxt

Originally posted by: Cabages

Why is everyone so concerned with the wheels? (real question)

Originally posted by: The Boston Dangler
i still don't get why people think the plane's speed relative to the ground matters.

There are essentially two ways to interpret the problem, and it concerns which rate of which object determines the rate of the conveyor belt. In one interpretation, the conveyor belt matches the speed of the plane's fuselage with respect to the ground. In another interpretation, the conveyor belt matches the speed of the angular rotation of the wheels.

Certain people seem to think that the latter interpretation is the more accurate interpretation. These also seem to be the only people left arguing that the plane does not take off, even though the only basis for such an argument involves absolutely ridiculous assumptions about the capacity of the conveyor belt to accelerate its surface sufficiently to magnify the second-order effects of the ordinarily-negligible friction between the bearings in the wheels and the axle and retard the forward motion of the plane such that it could not take off.

Except for smack Down, who seems to think that the angular momentum of a rotating wheel could somehow be magically transferred to an axle through frictionless bearings. He obviously lives in his own special reality.

Some people think the conveyor belt is supposed to always spin twice as fast as the wheels? How is that possible? That would mean X=2X

 

[smack Down]

Originally posted by: jmmtn4aj

Originally posted by: smack Down

Originally posted by: her209

Originally posted by: smack Down

Originally posted by: Cerpin Taxt
Question for you two: What if we assume that the wheels are connected to the axles by perfectly frictionless bearings? Can the conveyor retard the airplane's forward movement then?

Yes of course it can. If you wish to see that for yourself go get a wheel and put it on a treadmill. Turn on the treadmill and watch the wheel come back at you. Use a wheel with no axle ans you will have almost frictionless bearings.

Thank you for proving to us you have no idea what you are talking about.

So you think if I put a wheel on a treadmill it will just stay put?

Good god man, an undercarriage with frictionless bearings does NOT equal an unattached wheel! Jesus!

What happens to the forward force exerted on the wheel by the axle? Remove the axle and the force is gone, obviously.

Isn't this high school level physics?

My high school physics included a chapter on the fact that forces added. If the wheels would move backwards with no undercarriage attached then they would move backwards with an undercarriage attached with frictionless bearings.

 

[Throckmorton]

Originally posted by: JohnOfSheffield

If the conveyor belt is moving fast enough it will keep the plane in one place, no air passing the wings means no lifting power.

If you are not insane in the membrane you get this without a test.

Friction of wheels moving backwards at the same speed that the plane is propelled forwards means that the plane cannot move, it's as simple as shit and if you don't get it, you're retarded and i don't mean that in like "less knowledgeable" i really mean that you are fucked up in the skull in a way too serious to repair.

Quoted

 

[Throckmorton]

Originally posted by: bignateyk

Originally posted by: Squisher
As I posted in the other two threads:

If I'm flying a plane at 200mph and I hang out of it and affix a treadmill to the wheels which cause the wheels to spin at a rate that would generate a speed of 200mph backwards. Will the plane fall out of the sky?

no, because the plane is still moving at a speed relative to the ground, which will cause air to flow over the wings and the plane to have lift.

If the treadmill is on the ground and the plane has a ground speed of 0mph, then there will be no air flow over the wings, and no lift.

You are completely missing his point, which is that the speed of the treadmill has no effect on groundspeed.

 

[randay]

Originally posted by: Throckmorton

Some people think the conveyor belt is supposed to always spin twice as fast as the wheels? How is that possible? That would mean X=2X

half of them are trolls, half of them are just confused, and half of them are idiots. yes i know thats 3 halves.

 

[JRich]

For the third time, the plane takes off.

/thread

 

[Tweak155]

Originally posted by: randay

Originally posted by: Throckmorton

Some people think the conveyor belt is supposed to always spin twice as fast as the wheels? How is that possible? That would mean X=2X

half of them are trolls, half of them are just confused, and half of them are idiots. yes i know thats 3 halves.

Haha! QFT

 

[Gibsons]

Originally posted by: randay

Originally posted by: Throckmorton

Some people think the conveyor belt is supposed to always spin twice as fast as the wheels? How is that possible? That would mean X=2X

half of them are trolls, half of them are just confused, and half of them are idiots. yes i know thats 3 halves.

The three categories aren't mutually exclusive (i.e. someone can be both confused and an idiot) so it's logically consistent.

 

[Suspicious-Teach8788]

Originally posted by: spidey07

Originally posted by: Tweak155
THIS IS FOR ALL THOSE THAT THINK THE AIRPLANE WILL NOT TAKE OFF (offering a different way to prove to yourself that you're wrong):

Lets say an airplane is flying and is about to land. It lands on this conveyor belt that is moving the opposite direction the plane is traveling.

Do you REALLY believe that it is physically possible for the airplane to land on this conveyor belt and all of a sudden and sit still? This would require not moving forward an inch upon landing. I'll let you set the speed of the plane and the speed of the belt. If your numbers are outrageous, then I am allowed to insert that frictionless bearings and tire to conveyor belt friction is 0, which is also outrageous.

Car != airplane.

I realize this isn't the same scenario, but it helps illustrate that the airplane does not use the wheels/axles to move forward.

See - this is why people can't understand the physics involved. Hell, I was pretty good back when I flew RC planes so the principle of flight is so simple to me. I totally understand.

The question is a paradox. If you can't understand how and why the treadmill can retard the plane then you FAIL at physics.

Still everybody that believes a takeoff plane fails at physics. Imagine the original constraints of the problem and make your point.

Stop trying to imagine it in your mind and do the math.

Fail at physics? No, you must've only gotten as far as F=ma clearly because some of us got to rotation and for those of us who understand it, the wheels have nothing to do with stopping a plane.

Your argument is completely flawed. If I understand you properly, you're saying the treadmill CAN slow down a plane and so given that then it can't take off. What the hell? Since when does being able slowing a plane down = not being able to take off. That's like saying you can tap your brakes while gassing your car and still being able to speed up.

The original constraints of the problem? It states that the conveyor belt goes backwards as fast as the wheels are spinning forward right? But the wheels on the plane do not translate into linear motion of the plane itself. You can spin the wheels and treadmill as fast as you want, but the plane will do what the engines tell it to do in the end because the wheels have no effect.

Once again I want to say that we don't give a flying fvck about the friction between the wheel and bearings. If it means force of 500 lbs, so be it, but how does that even matter in the grand scheme of things when your engines are throwing out 90,000 lbs of thrust EACH? Stop considering friction because it's negligible, and it's not like your wheels can barely spin or anything.

 

[Cerpin Taxt]

Originally posted by: Throckmorton

Originally posted by: Cerpin Taxt

Originally posted by: Cabages

Why is everyone so concerned with the wheels? (real question)

Originally posted by: The Boston Dangler
i still don't get why people think the plane's speed relative to the ground matters.

There are essentially two ways to interpret the problem, and it concerns which rate of which object determines the rate of the conveyor belt. In one interpretation, the conveyor belt matches the speed of the plane's fuselage with respect to the ground. In another interpretation, the conveyor belt matches the speed of the angular rotation of the wheels.

Certain people seem to think that the latter interpretation is the more accurate interpretation. These also seem to be the only people left arguing that the plane does not take off, even though the only basis for such an argument involves absolutely ridiculous assumptions about the capacity of the conveyor belt to accelerate its surface sufficiently to magnify the second-order effects of the ordinarily-negligible friction between the bearings in the wheels and the axle and retard the forward motion of the plane such that it could not take off.

Except for smack Down, who seems to think that the angular momentum of a rotating wheel could somehow be magically transferred to an axle through frictionless bearings. He obviously lives in his own special reality.

Some people think the conveyor belt is supposed to always spin twice as fast as the wheels? How is that possible? That would mean X=2X

I don't know who you think those people are. Most rational people interpret the problem to describe the conveyor matching the speed of the plane's fuselage with respect to the ground. This would mean that the wheels would spin 2x faster than they would on a fixed surface, because the speed of the plane and the speed of the conveyor would be equivalent and additive when describing the angular rotation of the wheels.

 

[Cerpin Taxt]

Originally posted by: smack Down

Originally posted by: jmmtn4aj

Originally posted by: smack Down

Originally posted by: her209

Originally posted by: smack Down

Originally posted by: Cerpin Taxt
Question for you two: What if we assume that the wheels are connected to the axles by perfectly frictionless bearings? Can the conveyor retard the airplane's forward movement then?

Yes of course it can. If you wish to see that for yourself go get a wheel and put it on a treadmill. Turn on the treadmill and watch the wheel come back at you. Use a wheel with no axle ans you will have almost frictionless bearings.

Thank you for proving to us you have no idea what you are talking about.

So you think if I put a wheel on a treadmill it will just stay put?

Good god man, an undercarriage with frictionless bearings does NOT equal an unattached wheel! Jesus!

What happens to the forward force exerted on the wheel by the axle? Remove the axle and the force is gone, obviously.

Isn't this high school level physics?

My high school physics included a chapter on the fact that forces added. If the wheels would move backwards with no undercarriage attached then they would move backwards with an undercarriage attached with frictionless bearings.

Someone must have ripped out the chapter about inertia in that physics book of yours.

I repeat my earlier question (assuming frictionless bearings): How exactly would the treadmill deliver the energy to the axle in order to propel it backwards?

 

[jmmtn4aj]

Originally posted by: smack Down

Originally posted by: jmmtn4aj

Originally posted by: smack Down

Originally posted by: her209

Originally posted by: smack Down

Originally posted by: Cerpin Taxt
Question for you two: What if we assume that the wheels are connected to the axles by perfectly frictionless bearings? Can the conveyor retard the airplane's forward movement then?

Yes of course it can. If you wish to see that for yourself go get a wheel and put it on a treadmill. Turn on the treadmill and watch the wheel come back at you. Use a wheel with no axle ans you will have almost frictionless bearings.

Thank you for proving to us you have no idea what you are talking about.

So you think if I put a wheel on a treadmill it will just stay put?

Good god man, an undercarriage with frictionless bearings does NOT equal an unattached wheel! Jesus!

What happens to the forward force exerted on the wheel by the axle? Remove the axle and the force is gone, obviously.

Isn't this high school level physics?

My high school physics included a chapter on the fact that forces added. If the wheels would move backwards with no undercarriage attached then they would move backwards with an undercarriage attached with frictionless bearings.

When you remove the axle, you remove the axis of rotation, meaning whatever happens with the bearings stop mattering. without the axis of rotation, the wheel becomes just another object on a moving surface. Without an axle, frictional contact between the tire surface and the treadmill causes a horizontal force in the direction that the treadmill is moving. Sure, it might rotate if the treadmill accelerates fast enough, but that's because it's a round object and hence is inherent unstable. Place a tall block in it's place and if the acceleration is fast enough, it falls.

And it still doesn't not equate to an undercarriage with frictionless bearings. An undercarriage with frictionless bearings still provides and axis of rotation allowing the frictional force between the tire surface and treadmill to be converted to rotational motion, acting as torque, instead of moving the entire wheel back. Frictionless simply means no force is generate in the housing where the axle joins to the wheel. Friction in the bearing causes resistance to the wheels rotation. Resistance means the wheels RESIST rotation, meaning a horizontal force is generated even before it reaches the axle-wheel assembly, meaning it's like the free wheel (albeit on a negligible scale) where the wheels resistance to spinning creates a resultant force that tries to move the entire wheel back, and anything connected to it. Frictionless bearings won't have resistance to rotation, so no resultant force parallel to the ground is created, but it still has to spin around a point first.

God, that didn't really make sense. Tomorrow guys.

EDIT: New explanation below. This one is a little flawed in reasoning, sorry. I visualised this in a few minutes instead of trying some fbds

 

[smack Down]

Originally posted by: jmmtn4aj

Originally posted by: smack Down

Originally posted by: jmmtn4aj

Originally posted by: smack Down

Originally posted by: her209

Originally posted by: smack Down

Originally posted by: Cerpin Taxt
Question for you two: What if we assume that the wheels are connected to the axles by perfectly frictionless bearings? Can the conveyor retard the airplane's forward movement then?

Yes of course it can. If you wish to see that for yourself go get a wheel and put it on a treadmill. Turn on the treadmill and watch the wheel come back at you. Use a wheel with no axle ans you will have almost frictionless bearings.

Thank you for proving to us you have no idea what you are talking about.

So you think if I put a wheel on a treadmill it will just stay put?

Good god man, an undercarriage with frictionless bearings does NOT equal an unattached wheel! Jesus!

What happens to the forward force exerted on the wheel by the axle? Remove the axle and the force is gone, obviously.

Isn't this high school level physics?

My high school physics included a chapter on the fact that forces added. If the wheels would move backwards with no undercarriage attached then they would move backwards with an undercarriage attached with frictionless bearings.

When you remove the axle, you remove the axis of rotation, meaning whatever happens with the bearings stop mattering. without the axis of rotation, the wheel becomes just another object on a moving surface. Without an axle, frictional contact between the tire surface and the treadmill causes a horizontal force in the direction that the treadmill is moving. Sure, it might rotate if the treadmill accelerates fast enough, but that's because it's a round object and hence is inherent unstable. Place a tall block in it's place and if the acceleration is fast enough, it falls.

And it still doesn't not equate to an undercarriage with frictionless bearings. An undercarriage with frictionless bearings still provides and axis of rotation allowing the frictional force between the tire surface and treadmill to be converted to rotational motion, acting as torque, instead of moving the entire wheel back. Frictionless simply means no force is generate in the housing where the axle joins to the wheel. Friction in the bearing causes resistance to the wheels rotation. Resistance means the wheels RESIST rotation, meaning a horizontal force is generated even before it reaches the axle-wheel assembly, meaning it's like the free wheel (albeit on a negligible scale) where the wheels resistance to spinning creates a resultant force that tries to move the entire wheel back, and anything connected to it. Frictionless bearings won't have resistance to rotation, so no resultant force parallel to the ground is created, but it still has to spin around a point first.

God, that didn't really make sense. Tomorrow guys.

You know why it didn't make sense because it is wrong. Just as mass has a resistance to accelerating it also has a resistance to rotation. Both with and with out the axle the wheel has the same axis of rotation.

 

[rikadik]

Here's an analogy which may help whoever still thinks the plane won't take off. I know there are a few analogies that haven't been overly successful but I think this is a good although slight random one. I don't know if something similar has been suggested.

Imagine you're at the airport and there's one of those long moving walkways, and you put a trolley on it. And for the sake of the problem this trolley can move freely across the walkway - it's not one with those special wheels to stop it running out of control and crushing an unfortunate small child.

You put the trolley on the moving walkway, however you are NOT standing on the walkway, but ALONGSIDE the walkway on stationary land. The walkway is currently stationary. Picture the scene. You push the trolley forward, and as you do so the walkway begins to move in the opposite direction. Imagine actually doing this. Is the trolley going to move forward, or is the force you're applying somehow cancelled and you just can't move forward? No matter how hard you push you cannot move forward because the trolley itself cannot?

Of course the trolley would move forward. There would be some more resistance from the wheels but you'd easily overcome it. In this scenario the trolley is the plane and you are the engines. You are applying force to the trolley and your force is not affected by the moving walkway. You're generating force by pushing against the stationary ground with your feet just like the plane's engines push against the stationery air (let's forget about wind) providing forward movement.

Now imagine the above but this time you standing ON the walkway. In this case, you would not move because you are pushing against the walkway to create forward motion, but the walkway is moving away as you push it against giving you no net forward motion. This is what people must be imagining when they say the plane won't take off. But this is not what is happening. The force to move the plane forward is not generated at the wheels!

So... what I'm trying to say is... the plane takes off!

 

[Alistar7]

Does the plane in question have vectored thrust? If the jets can be positioned directly downards it will not matter, it will take off.

 

[LongCoolMother]

Originally posted by: rikadik
Here's an analogy which may help whoever still thinks the plane won't take off. I know there are a few analogies that haven't been overly successful but I think this is a good although slight random one. I don't know if something similar has been suggested.

Imagine you're at the airport and there's one of those long moving walkways, and you put a trolley on it. And for the sake of the problem this trolley can move freely across the walkway - it's not one with those special wheels to stop it running out of control and crushing an unfortunate small child.

You put the trolley on the moving walkway, however you are NOT standing on the walkway, but ALONGSIDE the walkway on stationary land. The walkway is currently stationary. Picture the scene. You push the trolley forward, and as you do so the walkway begins to move in the opposite direction. Imagine actually doing this. Is the trolley going to move forward, or is the force you're applying somehow cancelled and you just can't move forward? No matter how hard you push you cannot move forward because the trolley itself cannot?

Of course the trolley would move forward. There would be some more resistance from the wheels but you'd easily overcome it. In this scenario the trolley is the plane and you are the engines. You are applying force to the trolley and your force is not affected by the moving walkway. You're generating force by pushing against the stationary ground with your feet just like the plane's engines push against the stationery air (let's forget about wind) providing forward movement.

Now imagine the above but this time you standing ON the walkway. In this case, you would not move because you are pushing against the walkway to create forward motion, but the walkway is moving away as you push it against giving you no net forward motion. This is what people must be imagining when they say the plane won't take off. But this is not what is happening. The force to move the plane forward is not generated at the wheels!

So... what I'm trying to say is... the plane takes off!

nice analogy. kind of like an earlier one. imagine a roller skate on a treadmill. Turn the treadmill to max speed. Take your hand, push on the roller skate. What happens? Roller skate moves forward. Wheels have nothing to do with it.

Your hand is akin to the forward thrust generated by the turbine engines. What some people are getting mad about is friction in the axles/angular momentum. But cmon, do you REALLY think the problem was aiming at that?

 

[Auric]

Originally posted by: her209

Originally posted by: Throckmorton

Originally posted by: NanoStuff

Originally posted by: JujuFish
I can't believe this argument is still going on. The plane takes off.

Yes sir captain stupid.

The only way the plane wouldn't take off would be if the brakes were on.

Actually, quite the opposite. If the brakes were on such that the wheels could no turn, then the plane would slide across the treadmill until it gained enough speed and take off. The treadmill would never move because the wheels are locked and thus never violate the constraint.

Err, no. The tires would fail and the wheel assembly catch resulting in catastrophic failure and everyone DIAF.