Mythbusters punk'd whole internet

[coldmeat]

Originally posted by: waggy

Originally posted by: NanoStuff

Originally posted by: waggy
good diragram that shows what i mean


you guys are getting hung up on wheel speed and convyer belt speed. it really does not matter.

the wheels do not provide any power. all power comes from the engines. no matter what the plane is going ot go foreword. foreword motion is going to provide lift. so the plane takes off.

You're not about to understand this even if I tried my damn best trying to explain it, but it doesn't make a difference. If the wheels are tractionally bound to the ground, the plane's forward speed is directly proportional to the rotation of the wheels. If the conveyor belt compensates for the wheels, the plain goes nowhere, much like with a car. They have conveyor belts for testing cars, the cars don't take off, trust me.

wow..

there is a huge diffrence between a CAR and a plane. you put a car on the traedmill yes it wont take off. why? ITS A FUCKING CAR. the power is generated by the wheels.

With a plane its in the engines that produce thrust. with thrust the foreword mementom has nothing to do with the wheels. so you can ignore them. its going to move.

the 3rd law proves that..

:laugh: i just had to laugh

I agree, it will take off.

 

[waggy]

Originally posted by: smack Down

Originally posted by: ultimatebob

Originally posted by: DanTMWTMP

Originally posted by: lyssword
The plane takes off

/thread

oh wait..it airs in 1.5 hrs. haha.

I still got $5 on them NOT being able to take off. Never underestimate the Mythbuster's ability to defy Physics with Reality!

Physics and reality really have nothing to do with the question. It is all in how you define the control system on the treadmill. Make it match the ground speed the plane, or car takes off. Make it match the wheel speed plane or car stays put. Any idiot should be able to understand that.

hahahah

funny part is you think you are right.

 

[redgtxdi]

One of the things I love about this thread............(can't remember whether we covered it in the othe thread or not)............is that now there seem to be engineS!!! (plural).

#1.) There could possibly be a difference whether a single-prop was pushing air past the fuselage vs. twin engines pushing air past a more specific area of the wings themselves.

(Is #1 enough to enact Bernouli's principle??)

Again..........no problem w/ the treadmill/wheel scenario. People are gettin' waaaay too worked up over that part.

#2.) Where are flaps/ailerons?? UP?? DOWN?? LEVEL???

This too, will make a difference when the plane assumes take-off speed.


In the aggregate, however, the plane simply will not take off.

Another possible way to control the progressive movement of the plane would be to fabricate a type of "Smith" machine device where the wings could only move vertically, thus keeping the plane from moving forward, but allowing proof of actualy "lift".

Bottom line...............(unless we're talking about serious thrust as in "jet propulsion", the plane does NOT take off).

No Bernouli's principle.................no lift!

/thread

 

[spidey07]

Put a plane on a treadmill with engines off.

The plane will move backwards with wheels spinning.

Put a plane on same speed treadmill with small amount of thrust, plane stays still. Easy peasy. Now increase the thrust, hold the speed of the treadmill plane advances. No difficulty there.

BUT, I can match your advancement with an even faster treadmill to hold you if you follow the original paradox. That's the rub. If the plane advances you have broken one of the conditions. In otherwords, you're cheating.

Mythbusters? Of course the plane takes off because they don't posses the physically impossible treadmill of the original question.

 

[jagec]

Originally posted by: randay

Originally posted by: jagec
At that point you CAN actually match the so-called "wheel speed" of the plane with the treadmill.

You can never match treadmill speed with wheel speed. The wheel will always be moving faster then the treadmill. x=y=x+y

Disclaimer: Stopping an airplane from taking off by using a treadmill involves some rather unrealistic assumptions about the power of the treadmill and the robustness of the wheels.

BUT assuming a treadmill of arbitrarily high power, and indestructible wheels of nonzero mass (I'll throw frictionless bearings in there to keep it simple), the treadmill can slow down the plane by speeding up the wheels.

So,
we put a "speed sensor" with a wireless transmitter into the hub of one wheel. The treadmill is designed to match this measured speed in reverse.
Now the plane pulses its engines for a brief second, which causes it to begin moving forward with a small, constant speed. The treadmill accelerates to try and match this speed. The extra force is exerted on the wheels, which have a certain angular momentum. As long as the treadmill continues to accelerate and provide that force, it couples with an equal force at the hub to cause a torque and induce angular acceleration in the wheels. Well, that force at the hub is borrowed from the plane's momentum, since the engines are off. Eventually all of the momentum term is eaten up, the plane comes to a "stop", and the treadmill is now matching the wheel speed. Now that acceleration has stopped, the force on the wheels (and therefore angular acceleration) is back to nil, so the plane will sit in place for forever, barring frictional losses or further engine or treadmill inputs.

Another example: Get a Matchbox car, and one of those flywheel toy cars. Tie a string to the front of the Matchbox car, and measure the force required to keep it stationary on a treadmill. This will be a very small initial force as the wheels accelerate to the treadmill speed, and then an even smaller constant force to compensate for frictional losses. Repeat the experiment with the flywheel car. There will be a fairly substantial initial force as both the wheels and the flywheel accelerate to the treadmill speed, and then a much smaller constant force to compensate for frictional losses (slightly greater than the matchbox car, but a similar order of magnitude). Now accelerate the treadmill on both cars. The matchbox car's force will increase slightly, due to a tiny amount of angular momentum and slowly increasing frictional losses. The flywheel car's force will increase much more, and will remain at a constant high point (slowly increasing due to friction) as the treadmill maintains acceleration.

The way that the treadmill can overcome the force of the engines is through constant acceleration. I believe that once the plane runs out of fuel, the amount of energy tied up in angular momentum in its wheels will be roughly double the amount of energy that was extracted from the fuel (the treadmill contributes an equal amount of force in the opposite direction).

Originally posted by: smack Down
Physics and reality really have nothing to do with the question. It is all in how you define the control system on the treadmill. Make it match the ground speed the plane, or car takes off. Make it match the wheel speed plane or car stays put. Any idiot should be able to understand that.

Physics and reality have everything to do with control systems. The only reason that it is possible to design a control system which can keep the plane on the ground is because of a bizarre second-order force coupling (ignoring friction). If the plane was on skis, we assumed a frictionless environment, and the control system was ordered to "keep the plane stationary", it could not. You can't define the control system as working in way that defies physics, and call it a physics problem.

Originally posted by: Cerpin Taxt
I don't disagree, but I guess my point is that there must be an interval between the point where the disparity begins between the speeds of the wheels and treadmill, and the point where those second-order effects begin to affect the speed of the plane as you described. Thus, during the interval, the pre-conditions of the original problem are violated, making those preconditions impossible in operational terms. In other words, there isn't a real-world scenario where the preconditions would hold true at all times. Absent some qualifier in the original problem that the preconditions need not hold true during that interval, the preconditions are basically impossible.

Yes, there is an interval, but that just means that your error signal changed...which is how control systems work. Temperature controllers don't keep the room at EXACTLY 70 degrees, they fluctuate between slightly below and slightly above that, with the amount of fluctuation depending on the room, your heating apparatus, and the quality, type, and calibration of the controller.

Similarly, if the treadmill is ordered to "match the wheel speed", it will ramp up the acceleration of the treadmill (slowing down the plane via angular momentum) until it overshoots the mark and the plane actually starts moving backwards (while the treadmill continues to accelerate). Then it will decrease the acceleration until the plane catches up and starts moving forward again. And so on. To human eyes it may remain motionless, but that's just the hallmark of a good control system.

 

[smack Down]

Originally posted by: waggy

Originally posted by: smack Down

Originally posted by: ultimatebob

Originally posted by: DanTMWTMP

Originally posted by: lyssword
The plane takes off

/thread

oh wait..it airs in 1.5 hrs. haha.

I still got $5 on them NOT being able to take off. Never underestimate the Mythbuster's ability to defy Physics with Reality!

Physics and reality really have nothing to do with the question. It is all in how you define the control system on the treadmill. Make it match the ground speed the plane, or car takes off. Make it match the wheel speed plane or car stays put. Any idiot should be able to understand that.

hahahah

funny part is you think you are right.

Funny part is I know I'm right. Sad part is you think your right.

 

[Rubycon]

Why is this even debatable? How many folks have a treadmill? Oh wait I'm not going to go there but imagine this if you will!

If you put your hand inside a roller skate (inline skates will work too) and put it down on the treadmill that's moving away from your position (that would be the front of the machine) you most definitely CAN pull the skate towards yourself. It does not matter how fast the treadmill is moving. The wheels will move faster. I suppose if the treadmill had infinite power eventually the speed could be increased so fast the wheels would melt to it pulling the skate off your hand and hurling it through the wall BUT!!!

The point is the thrust from the engines is what moves the plane (this would be your hand) NOT the wheels ok? So the plane will move forward, fall off the belt and continue on a path. Planes are pretty heavy and landing gear fragile so it's a good bet that dropping off the belt is going to damage something and it probably won't take off. Or the experimenter who SWORE that the plane would not take off didn't plan for this does it inside a hangar only to have a real bad day when the wall gets remodeled by Boeing.

Heck if you put a Pratt & Whitney on top of a firebird and put the car on a treadmill it will run off! Tie it up with some rope and measure the thrust and keep the treadmills or dyno things whatever they're called for the vehicles that use their wheels for forward movement!

 

[LegendKiller]

Originally posted by: waggy

Originally posted by: smack Down

Originally posted by: ultimatebob

Originally posted by: DanTMWTMP

Originally posted by: lyssword
The plane takes off

/thread

oh wait..it airs in 1.5 hrs. haha.

I still got $5 on them NOT being able to take off. Never underestimate the Mythbuster's ability to defy Physics with Reality!

Physics and reality really have nothing to do with the question. It is all in how you define the control system on the treadmill. Make it match the ground speed the plane, or car takes off. Make it match the wheel speed plane or car stays put. Any idiot should be able to understand that.

hahahah

funny part is you think you are right.

Agreed, a guy with the name of "smack down" runs around pretending he knows everything, then when "smacked down" runs away like an Ike Turner smacked-up woman. Like, in this thread!

http://forums.anandtech.com/me...TMP=Linear&#lastunread

 

[smack Down]

Originally posted by: jagec

Originally posted by: randay

Originally posted by: jagec
At that point you CAN actually match the so-called "wheel speed" of the plane with the treadmill.

You can never match treadmill speed with wheel speed. The wheel will always be moving faster then the treadmill. x=y=x+y

Disclaimer: Stopping an airplane from taking off by using a treadmill involves some rather unrealistic assumptions about the power of the treadmill and the robustness of the wheels.

BUT assuming a treadmill of arbitrarily high power, and indestructible wheels of nonzero mass (I'll throw frictionless bearings in there to keep it simple), the treadmill can slow down the plane by speeding up the wheels.

So,
we put a "speed sensor" with a wireless transmitter into the hub of one wheel. The treadmill is designed to match this measured speed in reverse.
Now the plane pulses its engines for a brief second, which causes it to begin moving forward with a small, constant speed. The treadmill accelerates to try and match this speed. The extra force is exerted on the wheels, which have a certain angular momentum. As long as the treadmill continues to accelerate and provide that force, it couples with an equal force at the hub to cause a torque and induce angular acceleration in the wheels. Well, that force at the hub is borrowed from the plane's momentum, since the engines are off. Eventually all of the momentum term is eaten up, the plane comes to a "stop", and the treadmill is now matching the wheel speed. Now that acceleration has stopped, the force on the wheels (and therefore angular acceleration) is back to nil, so the plane will sit in place for forever, barring frictional losses or further engine or treadmill inputs.

Another example: Get a Matchbox car, and one of those flywheel toy cars. Tie a string to the front of the Matchbox car, and measure the force required to keep it stationary on a treadmill. This will be a very small initial force as the wheels accelerate to the treadmill speed, and then an even smaller constant force to compensate for frictional losses. Repeat the experiment with the flywheel car. There will be a fairly substantial initial force as both the wheels and the flywheel accelerate to the treadmill speed, and then a much smaller constant force to compensate for frictional losses (slightly greater than the matchbox car, but a similar order of magnitude). Now accelerate the treadmill on both cars. The matchbox car's force will increase slightly, due to a tiny amount of angular momentum and slowly increasing frictional losses. The flywheel car's force will increase much more, and will remain at a constant high point (slowly increasing due to friction) as the treadmill maintains acceleration.

The way that the treadmill can overcome the force of the engines is through constant acceleration. I believe that once the plane runs out of fuel, the amount of energy tied up in angular momentum in its wheels will be roughly double the amount of energy that was extracted from the fuel (the treadmill contributes an equal amount of force in the opposite direction).

Don't bother your trying to explain things involving momentum to fools who think it matters where a force is applied to a solid body. You might as wheel teach a dog long division you might have better luck. Just call them idiots and be done.

 

[ultimatebob]

Originally posted by: smack Down

Originally posted by: ultimatebob

Originally posted by: DanTMWTMP

Originally posted by: lyssword
The plane takes off

/thread

oh wait..it airs in 1.5 hrs. haha.

I still got $5 on them NOT being able to take off. Never underestimate the Mythbuster's ability to defy Physics with Reality!

Physics and reality really have nothing to do with the question. It is all in how you define the control system on the treadmill. Make it match the ground speed the plane, or car takes off. Make it match the wheel speed plane or car stays put. Any idiot should be able to understand that.

You're forgeting about option 3, though. The plane could get out of control and crash before it ever gets off the ground!

You HAVE watched the show before, right?

 

[mugs]

Originally posted by: ultimatebob
Really? Cool!

I'm putting down $5 Paypal on the plane NOT taking off

I'll take that bet, and I'll give you 1000 to 1 odds.

Actually I won't, because I don't know what wording of the question they'll be using.

 

[waggy]

Originally posted by: ultimatebob

Originally posted by: smack Down

Originally posted by: ultimatebob

Originally posted by: DanTMWTMP

Originally posted by: lyssword
The plane takes off

/thread

oh wait..it airs in 1.5 hrs. haha.

I still got $5 on them NOT being able to take off. Never underestimate the Mythbuster's ability to defy Physics with Reality!

Physics and reality really have nothing to do with the question. It is all in how you define the control system on the treadmill. Make it match the ground speed the plane, or car takes off. Make it match the wheel speed plane or car stays put. Any idiot should be able to understand that.

You're forgeting about option 3, though. The plane could get out of control and crash before it ever gets off the ground!

You HAVE watched the show before, right?

no no no..they will pack the plane with 200lbs of C4 and blow it up before it has a chance to do anything!

 

[NanoStuff]

Originally posted by: Rubycon
Why is this even debatable?

Because as you yourself prove, this is a confusing subject for most people.

For the plane, or any such object to advance forward, the wheels have to have equivalent angular momentum to the object's forward movement. If a belt compensates for all such momentum in the wheels, the object goes nowhere. You can push a roller skate on a treadmill simply because you're strong enough, not because the treadmill is out to stop you.

 

[coldmeat]

Originally posted by: NanoStuff

Originally posted by: Rubycon
Why is this even debatable?

Because as you yourself prove, this is a confusing subject for most people.

Rubycon has a better understanding than most people on here, including you.

 

[mugs]

Originally posted by: smack Down
Physics and reality really have nothing to do with the question.

Lollerskates.

 

[NanoStuff]

Originally posted by: coldmeat

Originally posted by: NanoStuff

Originally posted by: Rubycon
Why is this even debatable?

Because as you yourself prove, this is a confusing subject for most people.

Rubycon has a better understanding than most people on here, including you.

No she doesn't silly, otherwise she wouldn't be wrong.

 

[RapidSnail]

Originally posted by: smack Down
Don't bother your trying to explain things involving momentum to fools who think it matters where a force is applied to a solid body. You might as wheel teach a dog long division you might have better luck. Just call them idiots and be done.

Been done, with rooting thrown in as a bonus.

 

[Cerpin Taxt]

Originally posted by: NanoStuff

Originally posted by: Cerpin Taxt

That's due to inertia, not force delivered to the plane through the axles.

Ok, so place an unmoving plane on top of a conveyor belt and start up the conveyor belt. In fantasy land perhaps the plane would remain in place, but in the real world the plane would start moving back with the conveyor belt.

That's due to the minute amount of friction on the axles, but that force is negligible once the airplane engine begins to add propulsion to the body of the plane.

My theory is that magical fairies are moving the plane backwards with the conveyor belt, but suddenly disappear when the plane starts up it's engine. What's your theory?

You seem to think that the frictional forces on the axles are much more significant than they are in reality.

If what you claimed were true, no plane could take off if it were facing west.

 

[jagec]

Originally posted by: smack Down
Don't bother your trying to explain things involving momentum to fools who think it matters where a force is applied to a solid body. You might as wheel teach a dog long division you might have better luck. Just call them idiots and be done.

It DOES matter where the force is applied, since the body is not solid but is composed of a solid portion and an attached, but free-wheeling portion.

You've got the wrong idea about why it works, and the constraints under which it works. I seek to rectify that.

 

[NanoStuff]

Originally posted by: Cerpin Taxt

Originally posted by: NanoStuff

Originally posted by: Cerpin Taxt

That's due to inertia, not force delivered to the plane through the axles.

Ok, so place an unmoving plane on top of a conveyor belt and start up the conveyor belt. In fantasy land perhaps the plane would remain in place, but in the real world the plane would start moving back with the conveyor belt.

That's due to the minute amount of friction on the axles, but that force is negligible once the airplane engine begins to add propulsion to the body of the plane.

I'd like to hear your theory as to how a force that pulls a hundred ton object with itself is negligible.

 

[OulOat]

I think the easiest way to explain why a plane will take off is that there are 3 speeds. The speed of the plane, the speed of the plane wheels, and the speed of the treadmill.

Let's have several experiments changing the speed of the treadmill while keeping the speed of the plane at 100 mph.

1) The speed of the treadmill is 0 mph (ground). The speed of the wheels = The speed of the plane + 0 = 100 mph.
2) The speed of the treadmill is 100 mph. The speed of the wheels = The speed of the plane + the speed of the treadmill = 200 mph.
3) The speed of the treadmill is C. The speed of the wheels = The speed of the plane + the speed of the treadmill = 100 mph + C.

If the speed of the plane is not limited by the speed of the wheels, then it will take off. Because the wheels are an independent system that can rotate at their own speed, it doesn't really matter how fast the treadmill goes, the treadmill cannot apply any opposing force to the plane.

 

[dpert1]

holy hell, what is up with this

there is no way in hell the plane takes off, unless im misunderstanding this whole idea

moving air = lift

if the plane is stationary relative to the earth, it doesnt have air passing the wings. Why the hell do you think planes have airspeed indicators, without proper air speed, no lift. Period. Unless this strange idea has something to do with air passing the wings at a high rate of speed that i'm not getting, it doesnt leave the ground, the wheels just spin.

/physics major
//have flown cessna's before

 

[videogames101]

THEY ARE? holy fuck, no better way to say it. THIS IS SPARTA!!!!!!!!!!

EDIT: and for all those noobs out there, it wil not take off. For planes to have a different speed then the wheels there must be MOVING AIR beneath the plane's wings, hence, it's won't take off.


1000 to 1 odds to any takers,,,,

 

[smack Down]

Originally posted by: jagec

Originally posted by: smack Down
Don't bother your trying to explain things involving momentum to fools who think it matters where a force is applied to a solid body. You might as wheel teach a dog long division you might have better luck. Just call them idiots and be done.

It DOES matter where the force is applied, since the body is not solid but is composed of a solid portion and an attached, but free-wheeling portion.

You've got the wrong idea about why it works, and the constraints under which it works. I seek to rectify that.

Doesn't matter at the the force must be applies to the frame. F=ma learn it. If your car accelerates the the force must have been applies to it. It doesn't matter where.

 

[RapidSnail]

Originally posted by: dpert1
holy hell, what is up with this

there is no way in hell the plane takes off, unless im misunderstanding this whole idea

moving air = lift

if the plane is stationary relative to the earth, it doesnt have air passing the wings. Why the hell do you think planes have airspeed indicators, without proper air speed, no lift. Period. Unless this strange idea has something to do with air passing the wings at a high rate of speed that i'm not getting, it doesnt leave the ground, the wheels just spin.

/physics major
//have flown cessna's before

You're just misunderstanding like most people. The plane is moving and creating air flow, the only difference is that the wheels have to move twice as fast to compensate for the treadmill.