hmmm.... physics question for you guys....

[RobRR]

Re: hmmm.... physics question for you guys....

IF THE PLANE DOES NOT PHYSICALLY MOVE FOREWARD, THEN THE CONVEYOR DOES NOT MOVE. YOU MEASURE THE SPEED OF A PLANE FROM ITS MOVEMENT FROM A GIVEN POINT. HOW CAN THE CONVEYOR BE GOING 200 MPH REVERSE AND THE PLANE SITTING STILL? IT CANT, BECAUSE A PLANE SITTING STILL IS DOING 0 MPH NO MATTER HOW YOU LOOK AT IT.

[YetAnotherOne]

Re: hmmm.... physics question for you guys....

Yes Rob, I have a couple of engineering degrees that say that on a conveyer that perfectly matches the speed at which the plane is attempting to move, the plane will sit motionless from the perspective of a static observer on the tarmac (and from the perspective of the air surrounding the plane).

"Motionless" is a meaningless word unless you define your frame of reference. Move our static observer from the tarmac to the surface of the conveyer and the plane, rather than being motionless, will appear to the observer to be moving quickly away.

Similarly if you move the observer onto the plane the observer will note that neither he nor the plane is moving relative to the tarmac, airport, or the rest of the world. He will also note that the conveyer is moving very quickly relative to his position (and relative to the rest of the world).

Bottom line: the problem calls for a conveyer that matches the speed of the plane. Thus, by *definition* the force the plane exerts on the conveyer is equal to the force the conveyer exerts on the plane. When you later say that the plane will begin to move relative to the conveyer you've simply ignored the initial constraints of the problem. Not surprising that you're confused, when you change the rules mid-game that's usually the result.

[hippietim]

Re: hmmm.... physics question for you guys....

Guys, it's all a moot point. Today President Bush announced that the conveyer is in possession of weapons of mass destruction and has given the go ahead to invade it. Apparently his daddy is on the plane.

[hgsmith]

Re: hmmm.... physics question for you guys....

[ QUOTE ]


I wish I had an explanation.

[/ QUOTE ]

Aim for the red

[LouSiffer]

Re: hmmm.... physics question for you guys....

It is getting to be moot. Until all the people realize that since the planes propulsion is not reliant on the wheels, they will assume the plane will remain in the same place.

If this were a car on the conveyor belt, yes, it would remain motionless. matching the speed. This is because the car relies on it TIRES for propulsion. The conveyor is physically working against the propulsion of the car with direct contact.

A planes wheels do not propel the plane. They are just a neutral means.

Try this guys, and if I am wrong, I will leave this forum forever:

Take a skateboard to a checkout counter with the conveyor. Start at the end towards the cashier and push the skateboard with your finger against the direction of the conveyor. Your finger becomes the "jet" at this point. You are the propulsion for the skateboard, not the wheels it sits on. The wheels are neutral....they have no drive capabilities just like those on a plane. Now, tell me if you had to push twice as fast to get it to the other end, or if their was just minor extra force exerted due to the friction in the wheel bearings. -Lou

[hippietim]

Re: hmmm.... physics question for you guys....

Lou, you are not compensating for opposing force and resistance. How about we take the wheels off the skateboard?

How about we take the wheels off the airplane? Now will it take off?

[hippietim]

Re: hmmm.... physics question for you guys....

Lou, the difference between your skateboard at the checkout counter example vs. the problem as originally posed is that you didn't state the checkout counter conveyor would keep up with the speed of the skateboard. That is the one thing keeping you from having to leave the forum forever.

[LouSiffer]

Re: hmmm.... physics question for you guys....

Tim, since the wheels are in a neutral state, the only force relevant to the wheels is the friction in the bearings. Opposing force is irrelevent since the wheels are by no means a driving force. That is where all this confusions is coming from. People are assuming that the wheels are a driving force rather than a neutral force. Other than to help the plane roll, they are not.

The plane's momentum is caused by the thrust coming out of the jets and pushing on a wall of air behind it. Unless this is a magical conveyer belt that makes that air go away, it has no effect.

I stand by my statement. If I am wrong I will delete my account and leave the forum. I don't see anyone offer up the same thing from the opposition.

If you take the wheels off the plane and it is sitting directly on the conveyor, it probably will not take off. The reason is because there is no NEUTRAL moving piece of equipment now ( i.e. free spinning wheels ). The plane is in physical contact with the conveyor.

Again, go to a department store and try my idea with a skateboard. If I am wrong, I will leave. You will notice a little bit of drag caused by the bearings. If everyone was right about the it remaining motionless, that means you would come to a stop pushing it. You will not. You will be able to push it forward with only a slight increase in force due to the friction in the bearings.-Lou

[RobRR]

Re: hmmm.... physics question for you guys....

[ QUOTE ]
Yes Rob, I have a couple of engineering degrees that say that on a conveyer that perfectly matches the speed at which the plane is attempting to move, the plane will sit motionless from the perspective of a static observer on the tarmac (and from the perspective of the air surrounding the plane).



[/ QUOTE ]

Yeah, well Ive got zero degrees, and 24 years of real world experience and common sence. Its been made apparent in this thread, that a degree means just about as much as sunglasses on Helen Keller. [img]/images/graemlins/wink.gif[/img]

How could the plane sit motionless? When the thrusters are at full throttle, what FORCE would keep that plane in that one perticular spot? And even then, how could the plane have ANY speed, as it has NO air OR ground speed, so what is the moving conveyor basing its speed off of?

[RobRR]

Re: hmmm.... physics question for you guys....

Ill match Lou... If we are wrong, delete my account as well. I love this place and would never want to leave, but thats how sure I am that we are right. Im not just sure, Im 100% positive that the plane, at full thrust, will continue to move foreward from its origionating position, gain enough air speed to achieve lift then take off, just like a normal plane would. Only difference would be the wheels rotating at twice the speed, and minor parasthetic losses.

[hippietim]

Re: hmmm.... physics question for you guys....

[ QUOTE ]
Again, go to a department store and try my idea with a skateboard. If I am wrong, I will leave. You will notice a little bit of drag caused by the bearings. If everyone was right about the it remaining motionless, that means you would come to a stop pushing it. You will not. You will be able to push it forward with only a slight increase in force due to the friction in the bearings.-Lou

[/ QUOTE ]

Lou you are right about this because you didn't apply the original variable that the conveyor will compensate. The wheel is not a irrelevant in this example. Enough opposing force/resistance will stop the skateboard from making forward progress. Can I make a skateboard overcome a checkout counter conveyor? Absolutely. Can I make a skateboard overcome the mother of all speed compensating conveyors? Nope. Neither can you.

[StukaJU87]

Re: hmmm.... physics question for you guys....

Well, I have read the entire thread from beginng to end. At first I thought that the plane would not be able to take off. After reading all the explainations, I have been swayed. Since the airplane is pushing against the air, not the conveyor, I believe it would still move forward eventually gaining enough airspeed to rotate. The only issue I see, is if the bearings on the wheels could handle all that heat generated by the wheels turning so fast.

Am I on the right track Lou, Rob? [img]/images/graemlins/scratchhead.gif[/img]

[OnlineStageGear]

Re: hmmm.... physics question for you guys....

[ QUOTE ]
Guys, it's all a moot point. Today President Bush announced that the conveyer is in possession of weapons of mass destruction and has given the go ahead to invade it. Apparently his daddy is on the plane.

[/ QUOTE ]

That was only after being told by every agency we have and all the Intelligence agencies across the world that the conveyer had those weapons.

[RobRR]

Re: hmmm.... physics question for you guys....

Yes, your on the right track Stucka... Bearing failure, frictional loss' etc should all be taken into consideration in a real world scinario, but in this case they are details that wont majorly effect the outcome.

[FusionFarmer]

Re: hmmm.... physics question for you guys....

http://www.allstar.fiu.edu/aero/princ1.htm