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cdcox 06-04-2009 06:55 PM
1 Attachment(s)
Orange, you need to back track to the 2nd law.

For a normal jet the figure below shows the situation.

To keep the jet from accelerating you need to increase the rolling resistance so that it equals the jet thrust.

soundmind 06-04-2009 06:58 PM
None of this is in the Bible.

orange 06-04-2009 06:58 PM
Quote:
Originally Posted by cdcox (Post 5818183)
Orange, you need to back track to the 2nd law.

For a normal jet the figure below shows the situation.

To keep the jet from accelerating you need to increase the rolling resistance so that it equals the jet thrust.
No you don't. You're not putting a wall in front of the jet - you're moving the ground under it. As far as the jet's engines and wheels are concerned, the jet is moving. Its wings know the truth - no airflow.


ALL of the plane's movement along the ground MUST go through the wheels. They MUST roll or slide - whatever else are you imagining they do while this plane is mystically moving forward? And as they roll or slide, they exert force on the ground/treadmill - if the ground/treadmill moves freely, it will match the plane's "movement" and the plane remains in place.

I'm going to repeat this, because no one has even attempted an answer - ALL of the plane's movement along the ground MUST go through the wheels. They MUST roll or slide - whatever else are you imagining they do while this plane is mystically moving forward?

cdcox 06-04-2009 07:04 PM
Quote:
Originally Posted by orange (Post 5818190)
No you don't. You're not putting a wall in front of the jet - you're moving the ground under it. As far as the jet's engines and wheels are concerned, the jet is moving. Its wings know the truth - no airflow.
That's all well and good, as long as the forces balance, which they don't -- unless the treadmill adds a lot of rolling resistance. But once things get rolling, almost all the resistance comes from the bearing. The bearing doesn't know if it's rolling on tarmac or tread mill. The rolling resistance is going to be roughly the same.

Baby Lee 06-04-2009 07:04 PM
Quote:
Originally Posted by orange (Post 5818190)
No you don't. You're not putting a wall in front of the jet - you're moving the ground under it. As far as the jet's engines and wheels are concerned, the jet is moving. Its wings know the truth - no airflow.
Without friction, there is no couple between the jets and the conveyor.

Think of it this way, put a skateboard on a treadmill, anchor a rope to a wall, hop on the skateboard and start pulling yourself forward with the rope.

Absent friction, there is no speed at which the treadmill could be going the opposite way that could impede you moving forward by pulling the rope.

The external force of you pulling the rope, uncoupled to the treadmill below, is the same as the jet thrusters herein.

MagicHef 06-04-2009 07:07 PM
Quote:
Originally Posted by Baby Lee (Post 5818208)
Without friction, there is no couple between the jets and the conveyor.

Think of it this way, put a skateboard on a treadmill, anchor a rope to a wall, hop on the skateboard and start pulling yourself forward with the rope.

Absent friction, there is no speed at which the treadmill could be going the opposite way that could impede you moving forward by pulling the rope.

The external force of you pulling the rope, uncoupled to the treadmill below, is the same as the jet thrusters herein.
Why?

orange 06-04-2009 07:07 PM
Quote:
Originally Posted by Baby Lee (Post 5818208)
Without friction, there is no couple between the jets and the conveyor.

Think of it this way, put a skateboard on a treadmill, anchor a rope to a wall, hop on the skateboard and start pulling yourself forward with the rope.

Absent friction, there is no speed at which the treadmill could be going the opposite way that could impede you moving forward by pulling the rope.

The external force of you pulling the rope, uncoupled to the treadmill below, is the same as the jet thrusters herein.
Who said there's no friction? It won't roll if there's no friction - the skateboard will just slide effortlessly.

I've pointed out several times that more is better as far as friction between the wheels and treadmill.



[edit]
Quote:
Originally Posted by MagicHef (Post 5818213)
Why?
... or what HE said. :LOL:

Mizzou_8541 06-04-2009 07:08 PM
Quote:
Originally Posted by MediaCenterJunkie (Post 5816309)
3 friends go out to eat.

They get the bill and it is $25, but they don't really look at it too close.

They each give the waiter a $10 bill.

The Waiter decides since he cannot split $5 evenly among 3 people he decides to pocket $2, meaning the group paid a total of $27.

So the group paid $27 ($9 each), and he has $2 in his pocket, equaling $29.

What happened to the other dollar?
What restaurant are 3 people eating at for $25?

orange 06-04-2009 07:10 PM
Quote:
Originally Posted by Mizzou_8541 (Post 5818215)
What restaurant are 3 people eating at for $25?
Come to North Denver. There are plenty of little Mexican restaurants where you can do that. Don't expect to get the right change, though.

Hmmm. Maybe that's already where the problem is set.

Baby Lee 06-04-2009 07:11 PM
Quote:
Originally Posted by orange (Post 5818214)
Who said there's no friction? It won't roll if there's no friction - the skateboard will just slide effortlessly.

I've pointed out several times that more is better as far as friction between the wheels and treadmill.



[edit]

... or what HE said. :LOL:

Clarifying, not friction between the wheel and the ground, friction reeruning the rotation of the wheel.

You do get that there can be 'rolling without slippage' and still negligible reerunation of rotation, given negligent wheel mass and negligent bearing friction.

Think about the analogy and explain to me how you can pull yourself along the rope forward, no matter how fast the treadmill is going the opposite direction.

cdcox 06-04-2009 07:15 PM
Quote:
Originally Posted by orange (Post 5818214)
Who said there's no friction? It won't roll if there's no friction - the skateboard will just slide effortlessly.

I've pointed out several times that more is better as far as friction between the wheels and treadmill.



[edit]

... or what HE said. :LOL:
In classical physics, it is very common to describe something rolling frictionlessly, without sliding. What this means is that there is no energy lost due to friction in the rolling process. It does not mean that there is so little friction that there is a difference between the velocity of the road (or treadmill) and the road. In classical physics, you could say a car operating under normal conditions is rolling frictionlessly. Under braking conditions, friction is significant.

You would need friction to be equal to the jet thrust to keep the plane from moving relative to the ground.

Mizzou_8541 06-04-2009 07:15 PM
Quote:
Originally Posted by orange (Post 5818223)
Come to North Denver. There are plenty of little Mexican restaurants where you can do that. Don't expect to get the right change, though.

Hmmm. Maybe that's already where the problem is set.
:D

MagicHef 06-04-2009 07:17 PM
Quote:
Originally Posted by Baby Lee (Post 5818226)
Clarifying, not friction between the wheel and the ground, friction reeruning the rotation of the wheel.

You do get that there can be 'rolling without slippage' and still negligible reerunation of rotation, given negligent wheel mass and negligent bearing friction.

Think about the analogy and explain to me how you can pull yourself along the rope forward, no matter how fast the treadmill is going the opposite direction.
Stop it.

Psyko Tek 06-04-2009 07:17 PM
Quote:
Originally Posted by Jenson71 (Post 5816281)
This blows my mind.

Okay, say you have two ball bearings. You hold one in your hand and drop it. The other you put in a gun, point it straight forward, as level as the one in your hand, and pull the trigger, sending it hundreds of yards.

Which one lands first?

The one dropped in your hand right? RIGHT!?!?

No, actually they both hit the ground at the same time.

This is because the vertical component of motion is the same for both objects. They both fall vertically the same distance at about 10 meters per second squared (gravity, actually more like 9.8).

But Jenson, Jenson! What about the horizontal component of the gun-fired ball bearing? Actually, when air resistance is small enough to ignore as it is in this case (being that the bearings are exactly alike), the horizontal and vertical components of a projectile's velocity are completely independent of one another.

And, in this experiment, the gun-fired bearing is constantly falling from the moment it is fired. Yes, it looks like it is holding up in a straight line, but, it's actually falling and it's just hard to see with our eyes. And again, it is falling at exactly the same speed as the ball bearing you released in your hand -- the speed of gravity.

Post more cool science things in this thread.

I think I will later post Aristotle vs. Galileo and gravity, for a little history spin on science.
first joint?

orange 06-04-2009 07:18 PM
Quote:
Originally Posted by Baby Lee (Post 5818226)
Clarifying, not friction between the wheel and the ground, friction reeruning the rotation of the wheel.

You do get that there can be 'rolling without slippage' and still negligible reerunation of rotation, given negligent wheel mass and negligent bearing friction.

Think about the analogy and explain to me how you can pull yourself along the rope forward, no matter how fast the treadmill is going the opposite direction.
One - I think your analogy fails on a different point - anchoring the rope to the wall. To exert force using the rope, you have continually move your grip up the rope. Instead, put a huge wind machine fan behind you.

Two - In this instance, you will stand on the skateboard, the wheels will roll, the treadmill will roll under the wheels and you will remain in one spot.

[edit] Tried goodling "skateboard treadmill" to find a demonstration. I only see videos of failed attempts, so far, but I did find this on page one http://answers.google.com/answers/threadview?id=428718

This is a popular problem.

Baby Lee 06-04-2009 07:24 PM
Quote:
Originally Posted by MagicHef (Post 5818233)
Stop it.
Jesus Christ you are locked in. You stop.

Reality wins.

I get that your reading of the hypothetical demands Hurculean rolling resistance, otherwise the conveyor fails in it's job.

But since IN EVERY EMPIRICAL INSTANCE, bearing friction is in fact negligible wrt to 4 jumbo jet at full thrust, the conveyor WILL fail in it's job and the plane will take off.

Have you figured out how to stop me from inching forward as I pull the rope while I ride the skateboard on the treadmill, lemme guess superfriction always equalling and negating my muscle capacity.

I understand the conundrum, as well as you. This is getting tedious.

Baby Lee 06-04-2009 07:29 PM
Quote:
Originally Posted by orange (Post 5818236)
One - I think your analogy fails on a different point - anchoring the rope to the wall. To exert force using the rope, you have continually move your grip up the rope. Instead, put a huge wind machine fan behind you.

Two - In this instance, you will stand on the skateboard, the wheels will roll, the treadmill will roll under the wheels and you will remain in one spot.

[edit] Tried goodling "skateboard treadmill" to find a demonstration. I only see videos of failed attempts, so far, but I did find this on page one http://answers.google.com/answers/threadview?id=428718

This is a popular problem.
Yeah, there's only 300 pages on Mythbusters website. 300 pages, not posts, pages.

That's why this has gotten tedious. People keep reiterating the same hash of misconceptions and consequences of the ambiguity of the hypothetical.

headsnap 06-04-2009 07:37 PM
I can't believe that over 200 posts have been dedicated to this stoopid question...

Quote:
Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?
The bolded part is physically impossible realistically or theoretically, that is unless the treadmill is also powered by jet engines that accelerate the entire treadmill and conveyor belt at the opposite direction at the same rate the Jet accelerates, because unless the jet is anchored, it's gonna accelerate!


including the OP, there is a whole lotta' dumb in this thread...

cdcox 06-04-2009 07:41 PM
Imagine a person sitting in a chair, as wide and as long as the persons' ass. The person sitting in the chair pulls up on the seat of the chair with a force designed to exactly match the force needed to elevate the chair. Can the chair take off?

orange 06-04-2009 07:43 PM
Quote:
Originally Posted by Baby Lee (Post 5818256)
Yeah, there's only 300 pages on Mythbusters website. 300 pages, not posts, pages.
Quote:
Originally Posted by headsnap (Post 5818272)
I can't believe that over 200 posts have been dedicated to this stoopid question...
[/i]
This thread has already had an impact elsewhere on ChiefsPlanet: http://www.chiefsplanet.com/BB/showt...207709&page=17

orange 06-04-2009 07:46 PM
Quote:
Originally Posted by headsnap (Post 5818272)


The bolded part is physically impossible realistically or theoretically, that is unless the treadmill is also powered by jet engines that accelerate the entire treadmill and conveyor belt at the opposite direction at the same rate the Jet accelerates, because unless the jet is anchored, it's gonna accelerate!
In MY version - the treadmill is free-spinning. It does match the speed of the wheels perfectly, and it is also powered by jet engines - the same jet engines that are powering the plane.

orange 06-04-2009 07:47 PM
Quote:
Originally Posted by cdcox (Post 5818282)
Imagine a person sitting in a chair, as wide and as long as the persons' ass. The person sitting in the chair pulls up on the seat of the chair with a force designed to exactly match the force needed to elevate the chair. Can the chair take off?
I could do that easily (145 lbs.). I've known many people who would (and have) turned that chair into kindling.

headsnap 06-04-2009 07:48 PM
Quote:
Originally Posted by orange (Post 5818293)
powered by jet engines - the same jet engines that are powering the plane.
how?

cdcox 06-04-2009 07:50 PM
Quote:
Originally Posted by orange (Post 5818297)
I could do that easily (145 lbs.). I've know many people who would (and have) turned that chair into kindling.
What if the chair were infinitely strong (and frictionless)?

orange 06-04-2009 07:52 PM
Quote:
Originally Posted by headsnap (Post 5818299)
how?
As the wheels exert force against the treadmill due to the engine's thrust, the treadmill exerts an equal and opposite force against the wheels. This causes the wheels to roll. It also causes the free-spinning treadmill to roll in the opposite direction.

Use the advanced search for my posts in this thread. You might miss some of the comments to me by others, but I don't think so; I think I've quoted them all in my responses.

orange 06-04-2009 07:54 PM
Quote:
Originally Posted by cdcox (Post 5818304)
What if the chair were infinitely strong (and frictionless)?
Some of those people I mentioned have bought chairs they thought were infinitely strong and brought them to work.

The chairs weren't.

In any "irresistable force" vs. "immovable object" battle, bet on the fattest ass.

headsnap 06-04-2009 07:58 PM
Quote:
Originally Posted by orange (Post 5818308)
As the wheel exert force against the treadmill due to the engine's thrust, the treadmill exerts an equal and opposite force against the wheels. This causes the wheels to roll. It also causes the free-spinning treadmill to roll in the opposite direction.

Use the advanced search for my posts in this thread. You might miss some of the comments to me by others, but I don't think so; I think I've quoted them all in my responses.
so, you are saying that the jet engines are powering the wheels? :spock:


A jet powered by it's wheels might take off, but it will never fly... ;)

orange 06-04-2009 07:59 PM
Quote:
Originally Posted by headsnap (Post 5818316)
so, you are saying that the jet engines are powering the wheels? :spock:


A jet powered by it's wheels might take off, but it will never fly... ;)
Well, yeah. That's exactly my point. The plane will never fly.

headsnap 06-04-2009 08:00 PM
Quote:
Originally Posted by orange (Post 5818319)
Well, yeah. That's exactly my point. The plane will never fly.
did you know that jets are not propelled by their wheels?

orange 06-04-2009 08:02 PM
Quote:
Originally Posted by headsnap (Post 5818324)
did you know that jets are not propelled by their wheels?
Of course. Did you know it really doesn't matter?

Quote:
Originally Posted by orange (Post 5818190)

ALL of the plane's movement along the ground MUST go through the wheels. They MUST roll or slide* - whatever else are you imagining they do while this plane is mystically moving forward? And as they roll or slide, they exert force on the ground/treadmill - if the ground/treadmill moves freely, it will match the plane's "movement" and the plane remains in place.

I'm going to repeat this, because no one has even attempted an answer - ALL of the plane's movement along the ground MUST go through the wheels. They MUST roll or slide - whatever else are you imagining they do while this plane is mystically moving forward?

orange 06-04-2009 08:04 PM
* Consequences of failure to do so:

Quote:
Originally Posted by orange (Post 5818143)
The wheels simply MUST keep up with the rest of the plane or you get this:


http://www.airportpress.us/archive/v...p4art1pic2.jpg

BIMAN BANGLADESH MISHAP CLOSES AIRPORT
A Biman Bangladesh Airlines Airbus A310-300 has been involved in a take-off accident at Dubai International Airport, resulting in a temporary closure of the Gulf airport. The A310 – one of four operated by the airline, according to Flight’s ACAS database – was operating a service to Dhaka. Some reports suggest the aircraft suffered a tyre burst and/or nose-gear collapse during its take-off roll. Pictures of the accident show that the aircraft appears to have come to rest at the far end of Runway 12L with its nose gear collapsed.

headsnap 06-04-2009 08:05 PM
Quote:
Originally Posted by orange (Post 5818327)
Of course. Did you know it really doesn't matter?
are you really fucking serious!?!?!? LMAOLMAOLMAO



if DC wasn't enough, you and Jensen have removed any doubt in this thread...

MagicHef 06-04-2009 08:06 PM
This is awesome.

headsnap 06-04-2009 08:07 PM
Quote:
Originally Posted by orange (Post 5818339)
* Consequences of failure to do so:
all this time you have been talking about friction and failure of equipment... a goddamn plane crash? :shake:

MagicHef 06-04-2009 08:08 PM
Quote:
Originally Posted by cdcox (Post 5818304)
What if the chair were infinitely strong (and frictionless)?
No!!! Not frictionless!

orange 06-04-2009 08:09 PM
Quote:
Originally Posted by headsnap (Post 5818344)
are you really fucking serious!?!?!? LMAOLMAOLMAO
Yes, I am.

Answer this simple question, genius:


I'm going to repeat this, because no one has even attempted an answer - ALL of the plane's movement along the ground MUST go through the wheels. They MUST roll or slide - whatever else are you imagining they do while this plane is mystically moving forward?


The nose-down is an example of what happens when the wheels don't keep up with the rest of the plane. I'm sorry that's too complicated for you.

cdcox 06-04-2009 08:11 PM
Quote:
Originally Posted by orange (Post 5818356)
Yes, I am.

Answer this simple question, genius:


I'm going to repeat this, because no one has even attempted an answer - ALL of the plane's movement along the ground MUST go through the wheels. They MUST roll or slide - whatever else are you imagining they do while this plane is mystically moving forward?
They are rolling faster than the treadmill. Because they must (to account for the thrust of the engine).

orange 06-04-2009 08:13 PM
Quote:
Originally Posted by cdcox (Post 5818360)
They are rolling faster than the treadmill. Because they must (to account for the thrust of the engine).
They are not because they can't. They propel the treadmill. The energy from the engines' thrust moves the wheels and the treadmill equally.

http://www.sterndrive.info/sitebuild...nion_gears.jpg

headsnap 06-04-2009 08:15 PM
Quote:
Originally Posted by orange (Post 5818356)
Yes, I am.

Answer this simple question, genius:


I'm going to repeat this, because no one has even attempted an answer - ALL of the plane's movement along the ground MUST go through the wheels. They MUST roll or slide - whatever else are you imagining they do while this plane is mystically moving forward?
god you are dumb...

mystically moving forward? there is no mystic or magic behind F=MA!



Newton laughs at you while Galileo laughs at Jensen...

cdcox 06-04-2009 08:17 PM
Quote:
Originally Posted by orange (Post 5818363)
They are not because they can't. They propel the treadmill. The energy from the engines' thrust moves the wheels and the treadmill equally.
So if you put a sail on a roller skate and sit it on a treadmill there is no wind powerful enough to propel the roller skate forward?

headsnap 06-04-2009 08:18 PM
Quote:
Originally Posted by orange (Post 5818363)
They are not because they can't. They propel the treadmill. The energy from the engines' thrust moves the wheels and the treadmill equally.
for clarification, could you please post a picture of a JET that is entirely propelled by it's wheels?

orange 06-04-2009 08:18 PM
Quote:
Originally Posted by cdcox (Post 5818372)
So if you put a sail on a roller skate and sit it on a treadmill there is no wind powerful enough to propel the roller skate forward?
Not if the treadmill spins as freely as the skates. You get the gears analogy, right? You seem to be coming around.

orange 06-04-2009 08:19 PM
Quote:
Originally Posted by headsnap (Post 5818376)
for clarification, could you please post a picture of a JET that is entirely propelled by it's wheels?
Answer my question. Then I'll respond to you.

Your comment earlier just proves you have no answer.

Nighty-night.

headsnap 06-04-2009 08:19 PM
Quote:
Originally Posted by cdcox (Post 5818372)
So if you put a sail on a roller skate and sit it on a treadmill there is no wind powerful enough to propel the roller skate forward?
dun,not when the wind is also propelling the treadmill in the opposite direction...LMAO

headsnap 06-04-2009 08:21 PM
Quote:
Originally Posted by orange (Post 5818378)
Answer my question. Then I'll respond to you.

Your comment earlier just proves you have no answer.

Nighty-night.
your question is a plane crash... it's doesn't fly but it is most definitely moving forward.

One again, IS THIS PLANE ENTIRELY PROPELLED BY IT'S WHEELS?

headsnap 06-04-2009 08:22 PM
Quote:
Originally Posted by orange (Post 5818377)
Not if the treadmill spins as freely as the skates. You get the gears analogy, right? You seem to be coming around.
:LOL:LMAO

What force is counteracting the wind?

remember Newton...

prhom 06-04-2009 08:25 PM
Here's a cool experiment that's a pretty fun statics problem to prove. Take a yard stick or any stick like a dowel, spread out your hands and balance it on your index fingers. Then slide your hands toward each other. You will notice that the weight transfers between the two fingers until they come together. That point is the center of mass for that object.

cdcox 06-04-2009 08:26 PM
1 Attachment(s)
Quote:
Originally Posted by orange (Post 5818363)
They are not because they can't. They propel the treadmill. The energy from the engines' thrust moves the wheels and the treadmill equally.

http://www.sterndrive.info/sitebuild...nion_gears.jpg
Not this.

This.

orange 06-04-2009 08:31 PM
If that bar is free to move, it will move, the gear will spin and whatever is attached to that axle will stay where it is.

cdcox 06-04-2009 08:35 PM
Quote:
Originally Posted by orange (Post 5818413)
If that bar is free to move, it will move, the gear will spin and whatever is attached to that axle will stay where it is.
Both the bar and the gear are free to move relative to the ground. Their relative velocities will depend on the net force balances on the two objects.

headsnap 06-04-2009 08:35 PM
Quote:
Originally Posted by orange (Post 5818413)
If that bar is free to move, it will move, the gear will spin and whatever is attached to that axle will stay where it is.
not if I push it...

orange 06-04-2009 08:38 PM
Quote:
Originally Posted by cdcox (Post 5818424)
Both the bar and the gear are free to move relative to the ground. Their relative velocities will depend on the net force balances on the two objects.
I've pointed out that my treadmill must have equal or less resistance to spinning (i.e. moving forward in its own direction) than the plane has to going forward.

Keep in mind the gear IS moving. When it spins, it's moving. No forward movement by axle etal is necessary to satisfy that.

headsnap 06-04-2009 08:48 PM
Quote:
Originally Posted by headsnap (Post 5818383)
One again, IS THIS PLANE ENTIRELY PROPELLED BY IT'S WHEELS?
http://www.dcasali.com/images/filmnt...ales_frown.jpg

WELL?

cdcox 06-04-2009 08:52 PM
1 Attachment(s)
Quote:
Originally Posted by orange (Post 5818433)
I've pointed out that my treadmill must have equal or less resistance to spinning (i.e. moving forward in its own direction) than the plane has to going forward.
Okay.

prhom 06-04-2009 08:56 PM
Wow, I'm amazed that you guys are still arguing the plane on the treadmill. This is a classic physics test question that takes something that seems to complicate the problem (the treadmill) but is really just a distraction. Planes only fly based on AIRSPEED. Anything related to the groundspeed is irrelevant as to whether the plane will fly or not!! Besides, there would only be an extremely neglible force imparted to the treadmill by the plane's wheels. This would be from friction generated in the wheel bearings and rolling resistance in the tires. Bottom line the plane is going to fly no matter how fast or slow the treadmill is going.

orange 06-04-2009 08:57 PM
Nope. The force exerted by the jet on the treadmill and the force exerted by the treadmill on the jet are going to be exactly the same length - EQUAL AND OPPOSITE. You've just tossed out an example that assumes your final answer is right.

Once you make that adjustment, you then have to translate those forces into actual rotational velocity for the wheels and the treadmill. Since we are allowing for no sliding (as our starting point), you can set those velocities so that the "teeth per second" of both are equal and work backward to see the net forces.

orange 06-04-2009 08:59 PM
Quote:
Originally Posted by prhom (Post 5818513)
Wow, I'm amazed that you guys are still arguing the plane on the treadmill. This is a classic physics test question that takes something that seems to complicate the problem (the treadmill) but is really just a distraction. Planes only fly based on AIRSPEED. Anything related to the groundspeed is irrelevant as to whether the plane will fly or not!! Besides, there would only be an extremely neglible force imparted to the treadmill by the plane's wheels. This would be from friction generated in the wheel bearings and rolling resistance in the tires. Bottom line the plane is going to fly no matter how fast or slow the treadmill is going.
It will never fly, it will never move forward, there will never be any air over the wings. Its airspeed starts and remains 0. That's why planes take off from a runway. They have to build up to a high groundspeed before they can ever dream about airspeed.

prhom 06-04-2009 08:59 PM
Quote:
Originally Posted by orange (Post 5818516)
Nope. The force exerted by the jet on the treadmill and the force exerted by the treadmill on the jet are going to be exactly the same length - EQUAL AND OPPOSITE.
So you are arguing that the plane will not fly?

prhom 06-04-2009 09:04 PM
Quote:
Originally Posted by orange (Post 5818521)
It will never fly, it will never move forward, there will never be any air over the wings. Its airspeed starts and remains 0. That's why planes take off from a runway. They have to build up to a high groundspeed before they can ever dream about airspeed.
Wait just a minute orange, pilots NEVER care about groundspeed! If you were to tie a model plane to a string in a very high wind it could fly even though it's not moving relative to the ground. You can't deny that would be true.

headsnap 06-04-2009 09:06 PM
Quote:
Originally Posted by prhom (Post 5818513)
Wow, I'm amazed that you guys are still arguing the plane on the treadmill. This is a classic physics test question that takes something that seems to complicate the problem (the treadmill) but is really just a distraction. Planes only fly based on AIRSPEED. Anything related to the groundspeed is irrelevant as to whether the plane will fly or not!! Besides, there would only be an extremely neglible force imparted to the treadmill by the plane's wheels. This would be from friction generated in the wheel bearings and rolling resistance in the tires. Bottom line the plane is going to fly no matter how fast or slow the treadmill is going.
no, no, no, orange thinks the wheels are what makes a jet fly...


why else would it take bicycle makers to make the first airplane...

orange 06-04-2009 09:08 PM
Quote:
Originally Posted by prhom (Post 5818523)
So you are arguing that the plane will not fly?
Quote:
Originally Posted by prhom (Post 5818537)
Wait just a minute orange, pilots NEVER care about groundspeed! If you were to tie a model plane to a string in a very high wind it could fly even though it's not moving relative to the ground. You can't deny that would be true.
Yes.

When you're on the ground, yes. In this problem, the plane never acquires any airspeed - because it never moves from it's starting point. It actually never acquires any groundspeed either - but its wheels are spinning. All of the energy from that spinning is being transferred to the treadmill which is spinning under the plane.


Suppose we had an airplane that could take off on a windless day at 100 mph (liftoff airspeed is 100 mph). We are at an airport with an east-west runway that is 1 mile long. The wind is blowing 20 mph towards the west and the airplane takes off going east. The wind is blowing towards the aircraft which we call a headwind. Since we have defined a positive velocity to be in the direction of the aircraft's motion, a headwind is a negative velocity. While the plane is sitting still on the runway, it has a ground speed of 0 and an airspeed of 20 mph:

Airspeed = Ground Speed (0) - Wind Speed (-20) = 20 mph

The airplane starts its take off roll and has a constant acceleration a. From Newton's second law of motion, the ground speed V at any time t is:

V = a * t

and the distance d down the runway at any time is:

d = 1/2 * a * t^2

For a fixed length runway, this specifies the time to be used in the velocity equation. Let's assume that at 5000 feet down the runway, the velocity is 80 mph. Then the airspeed is given by

Airspeed = Ground Speed (80) - Wind Speed (-20) = 100 mph

and the airplane begins to fly. Now another pilot, with exactly the same airplane decides to take off to the west. The wind is now in the same direction as the motion and this is called a tailwind. The sign on the wind speed is now positive, not negative as with the headwind. The acceleration along the ground is the same, so at 5000 feet down the runway, the ground speed is again 80 mph. The airspeed is then given by:

Airspeed = Ground Speed (80) - Wind Speed (20) = 60 mph

This airplane doesn't have enough airspeed to fly. It runs off the end of the runway!


http://www.grc.nasa.gov/WWW/K-12/airplane/move.html

headsnap 06-04-2009 09:10 PM
1 Attachment(s)
Quote:
Originally Posted by cdcox (Post 5818491)
Okay.
a new question:

Q: Orange's Smart Car is traveling 60mph southbound, my Nissan Aramada is traveling 60 mph northbound and we hit head on.

A: I am traveling 30mph northbound and orange is traveling to the morgue.

headsnap 06-04-2009 09:11 PM
Quote:
Originally Posted by orange (Post 5818547)
Yes.

When you're on the ground, yes. In this problem, the plane never acquires any airspeed - because it never moves from it's starting point. It actually never acquires any groundspeed either - but its wheels are spinning. All of the energy from that spinning is being transferred to the treadmill which is spinning under the plane.
HOW????

cdcox 06-04-2009 09:11 PM
Quote:
Originally Posted by orange (Post 5818516)
Nope. The force exerted by the jet on the treadmill and the force exerted by the treadmill on the jet are going to be exactly the same length - EQUAL AND OPPOSITE. You've just tossed out an example that assumes your final answer is right.

Once you make that adjustment, you then have to translate those forces into actual rotational velocity for the wheels and the treadmill. Since we are allowing for no sliding (as our starting point), you can set those velocities so that the "teeth per second" of both are equal and work backward to see the net forces.
Your equal and opposite forces between the gear and the bar are true, consider it another set of equal sized arrows between the two diagrams. I tossed out an example that showed that your statement of less resistance in the treadmill doesn't preclude my argument.

Say the teeth per second relative to each other is 10. You could get that by having the jet moving forward at 9 teeth per second relative to the ground and the bar moving backward at 1 tooth per second relative to the ground.

Pitt Gorilla 06-04-2009 09:13 PM
Physics 101. Good stuff.

headsnap 06-04-2009 09:14 PM
Quote:
Originally Posted by Pitt Gorilla (Post 5818562)
Physics 101. Good stuff.
it's almost as bad as Econ 101 over in DC...

prhom 06-04-2009 09:17 PM
Quote:
Originally Posted by orange (Post 5818547)
Yes.

When you're on the ground, yes. In this problem, the plane never acquires any airspeed - because it never moves from it's starting point. It actually never acquires any groundspeed either - but its wheels are spinning.
I don't think there's anyway I convince you otherwise unless I draw a force diagram for the landing gear. You're equal and opposite force comment tells me you are thinking of the the wheels as a fixed entity. In reality the equal and opposite forces acting on the wheel are a force couple. One force being the axle pushing forward from the center of the wheel. The other force is the friction force between the wheel and treadmill. All this is going to do is make the wheel spin. The only forces that can affect the plane are friction forces in the wheel bearings and rolling resistance. These would be too complicated to draw up and I just don't have the motivation to do it...yet.

orange 06-04-2009 09:20 PM
Quote:
Originally Posted by cdcox (Post 5818558)
Your equal and opposite forces between the gear and the bar are true, consider it another set of equal sized arrows between the two diagrams. I tossed out an example that showed that your statement of less resistance in the treadmill doesn't preclude my argument.

Say the teeth per second relative to each other is 10. You could get that by having the jet moving forward at 9 teeth per second relative to the ground and the bar moving backward at 1 tooth per second relative to the ground.
That would require some resistance to cause the bar to move less rapidly than the jet. My free-spinning treadmill (bar) has no such resistance. It will move at 5 tps to match the jet's 5 tps.

headsnap 06-04-2009 09:21 PM
Quote:
Originally Posted by orange (Post 5818582)
That would require some resistance to cause the bar to move less rapidly than the jet. My free-spinning treadmill (bar) has no such resistance. It will move at 5 tps to match the jet's 5 tps.
HOW IS THE JET PUSHING THE TREADMILL?

orange 06-04-2009 09:21 PM
Quote:
Originally Posted by prhom (Post 5818578)
I don't think there's anyway I convince you otherwise unless I draw a force diagram for the landing gear. You're equal and opposite force comment tells me you are thinking of the the wheels as a fixed entity. In reality the equal and opposite forces acting on the wheel are a force couple. One force being the axle pushing forward from the center of the wheel. The other force is the friction force between the wheel and treadmill. All this is going to do is make the wheel spin. The only forces that can affect the plane are friction forces in the wheel bearings and rolling resistance. These would be too complicated to draw up and I just don't have the motivation to do it...yet.
The bolded statement is incorrect. The force at that friction point is going to make the treadmill spin equally and opposite.

I put up an illustration of this earlier:

Quote:
Originally Posted by orange (Post 5817811)
http://upload.wikimedia.org/wikipedi...Resistance.PNG

Not a perfect illustration but something to work with.


Let's say there is a point n where the vector N meets the circle. Let's add that this is the only point where the wheel meets the treadmill.

When the engines exert thrust (in direction -F) the plane tries to move forward F. Friction resists wheel point n moving. We are assuming this friction is high enough to stop n's motion, causing rolling and preventing sliding.

This happens because wheel point n pushes (i.e. exerts force) against treadmill point n. The resistance pushes back with an equal and opposite force, stopping the wheel from sliding. The energy from this causes the wheel to rotate forward (i.e. roll).

The force from the wheel against the treadmill also pushes the treadmill, causing it to rotate backward relative to the wheel.

These forces act equally and simultaneously. All the energy involved is from the engine, transmitted through the suspension and wheels.


p.s. Did you catch my groundspeed during takeoff example above? It took a few minutes to find a good, simple one, but I don't want you to miss it. You'll continue to think that pilots never are concerned with groundspeed.

headsnap 06-04-2009 09:23 PM
Quote:
Originally Posted by orange (Post 5818585)
The bolded statement is incorrect. The force at that friction point is going to make the treadmill spin equally and opposite.
LMAO

again, what force?

prhom 06-04-2009 09:24 PM
Quote:
Originally Posted by orange (Post 5818582)
That would require some resistance to cause the bar to move less rapidly than the jet. My free-spinning treadmill (bar) has no such resistance. It will move at 5 tps to match the jet's 5 tps.
Argh! What resistance is the wheel going to have?!? There are no gears in the landing wheels! Why do you think they have to push the jets back from the concourse? If those wheels were geared they could just reverse them.

orange 06-04-2009 09:27 PM
Quote:
Originally Posted by prhom (Post 5818594)
Argh! What resistance is the wheel going to have?!? There are no gears in the landing wheels! Why do you think they have to push the jets back from the concourse? If those wheels were geared they could just reverse them.
It's not the resistance in the gears. It's air resistance against the plane, etc. - and the simple inertia that it must overcome to get that mass into motion.

How many times am I going to have to post this:

Quote:
Originally Posted by orange (Post 5817811)
http://upload.wikimedia.org/wikipedi...Resistance.PNG

Not a perfect illustration but something to work with.


Let's say there is a point n where the vector N meets the circle. Let's add that this is the only point where the wheel meets the treadmill.

When the engines exert thrust (in direction -F) the plane tries to move forward F. Friction resists wheel point n moving. We are assuming this friction is high enough to stop n's motion, causing rolling and preventing sliding.

This happens because wheel point n pushes (i.e. exerts force) against treadmill point n. The resistance pushes back with an equal and opposite force, stopping the wheel from sliding. The energy from this causes the wheel to rotate forward (i.e. roll).

The force from the wheel against the treadmill also pushes the treadmill, causing it to rotate backward relative to the wheel.

These forces act equally and simultaneously. All the energy involved is from the engine, transmitted through the suspension and wheels.

prhom 06-04-2009 09:28 PM
Quote:
Originally Posted by orange (Post 5818585)
The bolded statement is incorrect. The force at that friction point is going to make the treadmill spin equally and opposite.

I put up an illustration of this earlier:





p.s. Did you catch my groundspeed during takeoff example above? It took a few minutes to find a good, simple one, but I don't want you to miss it. You'll continue to think that pilots never are concerned with groundspeed.
Yes, you are 100% correct that the FRICTION and ROLLING resistance (I don't know how to work the bold tags or I would bold that) force would act equally on the treadmill. What you are missing is that the FRICTION and ROLLING resistance forces are very very small. Therefore, the NET force on the plane is positive enabling it to take off.

MagicHef 06-04-2009 09:29 PM
I'm sorry, everyone.

orange 06-04-2009 09:30 PM
Quote:
Originally Posted by prhom (Post 5818605)
Yes, you are 100% correct that the FRICTION and ROLLING resistance (I don't know how to work the bold tags or I would bold that) force would act equally on the treadmill. What you are missing is that the FRICTION and ROLLING resistance forces are very very small. Therefore, the NET force on the plane is positive enabling it to take off.
Answer this:

Quote:
Originally Posted by orange (Post 5818190)

ALL of the plane's movement along the ground MUST go through the wheels. They MUST roll or slide - whatever else are you imagining they do while this plane is mystically moving forward? And as they roll or slide, they exert force on the ground/treadmill - if the ground/treadmill moves freely, it will match the plane's "movement" and the plane remains in place.

I'm going to repeat this, because no one has even attempted an answer - ALL of the plane's movement along the ground MUST go through the wheels. They MUST roll or slide - whatever else are you imagining they do while this plane is mystically moving forward?

headsnap 06-04-2009 09:31 PM
Quote:
All the energy involved is from the engine, transmitted through the suspension and wheels.
it's a JET, how is this happening?

headsnap 06-04-2009 09:32 PM
Quote:
Originally Posted by orange (Post 5818613)
Answer this:
because it DOESN'T go through the wheels... LMAO


dumbass...

headsnap 06-04-2009 09:33 PM
Quote:
Originally Posted by MagicHef (Post 5818609)
I'm sorry, everyone.
unless my sarcasmometer is on the fritz, you are almost as bad as our donkey friend... ;)

prhom 06-04-2009 09:34 PM
Orange, I will answer your question in post #396. Give me a second to write the response. I also didn't respond to your wheel force diagram because I didn't see it. Answer is pending...


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