Will the plane takeoff?

[Wisha Haddan H3]

Originally Posted by PARAGON

That's not true. Newton's law of motion states that the rocket or plane wants to stay still. As power is applied, as soon as it wants to start to roll, the conveyor moves, sending the motion back to a zero point.

That's where the conundrum lies with this version of the question. The plane can really never get up to any speed because it can't get past zero simply due to the limitations of the question IF you make certain assumptions OR it will take off IF you make other assumptions.

If the speed of the plane will always be instantaneously matched, the forward movement of the plane will never increase relative to it's surroundings.

If the plane starts to move at x MPH and instaneously the belt moves it -X MPH, the body of the plane remains still and actually does not move from a math standpoint.

But, assuming it's not a fictional question and the plane can move past this fictional "barrier of movement" then, as the plane increases it's speed, the plane is moving through the air and the belt is moving beneath and theoretically moving the wheels twice as fast.

That's why there were apparently different versions of the question. The one here was too vague and allowed for the No answer to be argued. The ones Bluehummer posted, that said speed relative to the wheels, changes the whole argument and allows the "body" of the plane to move without respect to the wheels.

Thank you for the coherent explanation. The only flaw in your evaluation lies in your application of the 3rd law of motion. "For every action there is an equal and opposite reaction".

A car on the conveyor would behave exactly as you describe, since its forward motion is dependent on the force its wheels apply to the conveyor surface. The wheels turn, exerting rearward force on the conveyor belt. The conveyor rolls, absorbing the force and negating forward motion relative to the ground next to the conveyor and the air around it. In other words, although the car moves forward relative to the conveyor, it remains stationary relative to the ground and air.

However, an airplane doesn't have drive wheels. Its forward motion depends the force of the props applied directly to the air. The props turn, exerting force on the air. As air is pushed rearward, the props are pushed in the opposite direction and the plane moves forward through the air, rolling over the conveyor's surface. Meanwhile the conveyor tries to spin, as if to counteract the forward motion of the plane, but the plane's wheels roll freely over it at higher and higher speeds. As the props push air rearward, the wings slice through the static air around the plane until the airflow over the wings produces enough lift for takeoff.

Nothing can stop the plane from taking off unless the tires blow out. Then, the extra friction between the landing gear and the conveyor could crash the plane or slow it down enough to prevent takeoff velocity.

[PARAGON]

Originally Posted by Wisha Haddan H3

Thank you for the coherent explanation. The only flaw in your evaluation lies in your application of the 3rd law of motion. "For every action there is an equal and opposite reaction".

A car on the conveyor would behave exactly as you describe, since its forward motion is dependent on the force its wheels apply to the conveyor surface. The wheels turn, exerting rearward force on the conveyor belt. The conveyor rolls, absorbing the force and negating forward motion relative to the ground next to the conveyor and the air around it. In other words, although the car moves forward relative to the conveyor, it remains stationary relative to the ground and air.

However, an airplane doesn't have drive wheels. Its forward motion depends the force of the props applied directly to the air. The props turn, exerting force on the air. As air is pushed rearward, the props are pushed in the opposite direction and the plane moves forward through the air, rolling over the conveyor's surface. Meanwhile the conveyor tries to spin, as if to counteract the forward motion of the plane, but the plane's wheels roll freely over it at higher and higher speeds. As the props push air rearward, the wings slice through the static air around the plane until the airflow over the wings produces enough lift for takeoff.

Nothing can stop the plane from taking off unless the tires blow out. Then, the extra friction between the landing gear and the conveyor could crash the plane or slow it down enough to prevent takeoff velocity.

You simply don't get it. It has nothing to do with it.

The question itself is self-limiting. Regardless of tires, planes, trains or automobiles. The moment it states that the conveyor will match speed with the airplane, period, it is stating that the plane will never move relative to the air. It will never gain speed.

Has nothing to do with physics. It's logic being applied to the question. THAT'S THE REASON FOR THE YES/NO ANSWER.

The question is in itself flawed.

The crap you are reading on some physics site is accurate if you pose the question where the speed is relative to the planes wheels or relative to anything. But since it is left wide open, an assumption would have to be made to suggest that the plane ever moves.

The reason is because due to the limits of the question, it's suggesting that the plane never breaks from zero speed.

It doesn't matter what type of propulsion is used. Whether its magnetic, some big hand, jet, prop, plasmic or whatever. The plane can never move simply because the equation offered by the question says it can't.

[Wisha Haddan H3]

Originally Posted by PARAGON

You simply don't get it. It has nothing to do with it.

The question itself is self-limiting. Regardless of tires, planes, trains or automobiles. The moment it states that the conveyor will match speed with the airplane, period, it is stating that the plane will never move relative to the air. It will never gain speed.

Has nothing to do with physics. It's logic being applied to the question. THAT'S THE REASON FOR THE YES/NO ANSWER.

The question is in itself flawed.

The crap you are reading on some physics site is accurate if you pose the question where the speed is relative to the planes wheels or relative to anything. But since it is left wide open, an assumption would have to be made to suggest that the plane ever moves.

The reason is because due to the limits of the question, it's suggesting that the plane never breaks from zero speed.

It doesn't matter what type of propulsion is used. Whether its magnetic, some big hand, jet, prop, plasmic or whatever. The plane can never move simply because the equation offered by the question says it can't.

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction) instantly.

Will the plane be able to take off?

The question is not flawed. It also never states the plane never breaks from zero speed. It is clear, direct and perfectly logical. Here's why. The conveyor can match the plane's forward velocity in the opposite direction because it is not connected to the airplane in any way, neither by physical attachments nor by forces. Since the airplane rolls on wheels, it can move forward at 100 knots while the conveyor moves backward at 100 knots. The relative speed between the two is 200 knots, and there is no contradiction in either logic or physics. Or the conveyor can move forward with the plane so the relative speed between them is 0 knots. Either way, the plane is moving at 100 knots relative to the air it is pushing through.

There is a logical flaw but it lies in your assumption that the relative speed between the plane and the conveyor determines the relative speed between the plane and the static air around it.

A ground-based conveyor cannot hold back a freewheeling vehicle that uses air for its locomotion. If the scenario involved an airplane in a wind tunnel, a submarine in a water current, a car on a conveyor or any vehicle where the medium of propulsion could be reversed, you would be absolutely correct. But that's not the case here.

The conveyor is a ground-based reversal, but the air around the airplane hasn't been touched. It remains static and the props can pull the airplane through it, causing airflow, lift and takeoff. This is the correct solution to the riddle.
______________

To me what makes this question interesting isn't just the physics. It's our human approach to the problem. Human experience is ground-based. We see birds and airplanes fly, but we cannot. Whether we walk, drive, skate or bicycle, we depend on forces pushing against the ground for locomotion. So our instinctive approach to this problem is also ground-based.

When we imagine ourselves on a conveyor, we realize that unless we walk on it, it will carry us along. We also realize that if the conveyor matches our walking speed, our position relative to the ground and air next to us will remain the same.

Our experience tells us that if we put an airplane on the conveyor, it will also be carried along, and if it tries to move forward it will also remain in the same place relative to the ground and air next to it. We also know that lift requires airflow, and if the plane's position is stationary relative to the air, there can be no lift and it cannot take off.

We assume all this from our ground-based experience ... but the reality is counter-intuitive.

First, there's the question of friction on the conveyor. When we stand on a treadmill, our feet stick to it through friction and we are pulled along unless we walk. However, the airplane is mounted on wheels that roll freely on it. It does not stick to the conveyor and is not pulled backwards as we would be. Thus, the conveyor cannot hold the airplane back.

Second, there's the question of propulsion. When we walk on a conveyor, our movement results from pushing against the moving conveyor with our feet. However, an airplane doesn't drive on the conveyor using its wheels ... the wheels roll freely over the conveyor, as the props push against the static air above it. Newton's 3rd law allows the plane to move forward, independently of the ground-based conveyor. The wing is drawn through the static air around it and the resulting airflow creates lift, allowing the plane to take off.

Thus, the speed and direction of the conveyor below the plane is irrelevant unless the tires blow.

[PARAGON]

Originally Posted by Wisha Haddan H3

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction) instantly.

Will the plane be able to take off?

The question is not flawed. It also never states the plane never breaks from zero speed. It is clear, direct and perfectly logical. Here's why. The conveyor can match the plane's forward velocity in the opposite direction because it is not connected to the airplane in any way, neither by physical attachments nor by forces. Since the airplane rolls on wheels, it can move forward at 100 knots while the conveyor moves backward at 100 knots. The relative speed between the two is 200 knots, and there is no contradiction in either logic or physics. Or the conveyor can move forward with the plane so the relative speed between them is 0 knots. Either way, the plane is moving at 100 knots relative to the air it is pushing through.

There is a logical flaw but it lies in your assumption that the relative speed between the plane and the conveyor determines the relative speed between the plane and the static air around it.

A ground-based conveyor cannot hold back a freewheeling vehicle that uses air for its locomotion. If the scenario involved an airplane in a wind tunnel, a submarine in a water current, a car on a conveyor or any vehicle where the medium of propulsion could be reversed, you would be absolutely correct. But that's not the case here.

The conveyor is a ground-based reversal, but the air around the airplane hasn't been touched. It remains static and the props can pull the airplane through it, causing airflow, lift and takeoff. This is the correct solution to the riddle.
______________

To me what makes this question interesting isn't just the physics. It's our human approach to the problem. Human experience is ground-based. We see birds and airplanes fly, but we cannot. Whether we walk, drive, skate or bicycle, we depend on forces pushing against the ground for locomotion. So our instinctive approach to this problem is also ground-based.

When we imagine ourselves on a conveyor, we realize that unless we walk on it, it will carry us along. We also realize that if the conveyor matches our walking speed, our position relative to the ground and air next to us will remain the same.

Our experience tells us that if we put an airplane on the conveyor, it will also be carried along, and if it tries to move forward it will also remain in the same place relative to the ground and air next to it. We also know that lift requires airflow, and if the plane's position is stationary relative to the air, there can be no lift and it cannot take off.

We assume all this from our ground-based experience ... but the reality is counter-intuitive.

First, there's the question of friction on the conveyor. When we stand on a treadmill, our feet stick to it through friction and we are pulled along unless we walk. However, the airplane is mounted on wheels that roll freely on it. It does not stick to the conveyor and is not pulled backwards as we would be. Thus, the conveyor cannot hold the airplane back.

Second, there's the question of propulsion. When we walk on a conveyor, our movement results from pushing against the moving conveyor with our feet. However, an airplane doesn't drive on the conveyor using its wheels ... the wheels roll freely over the conveyor, as the props push against the static air above it. Newton's 3rd law allows the plane to move forward, independently of the ground-based conveyor. The wing is drawn through the static air around it and the resulting airflow creates lift, allowing the plane to take off.

Thus, the speed and direction of the conveyor below the plane is irrelevant unless the tires blow.

The logic simply eludes you.

You are making an assumption to come to your conclusion. An assumption that is not offered by the question.

tracks the plane's speed

plane's speed relative to what? Relative to the conveyor? Airspeed, relative to the surrounding air?

If it's airspeed, the very point at which the plane breaks the hold and theoretically begins to move, the conveyor would be moving it backwards and the wheels would never rotate and the plane would remain stationary. The plane is not being held stationary by any physical force, it's being held by the question. You have to assume that the plane starts to move and rotate the tires for the plane to gain airspeed. Well the question limits this assumption because one can make an assumption that allows for a different answer, therefore the question is flawed in that it allows for a yes and an no answer.

If you can't see the simplicity of logic. I can't help further.

You have to go and make it "fit" into

[Wisha Haddan H3]

Originally Posted by PARAGON

The logic simply eludes you.

You are making an assumption to come to your conclusion. An assumption that is not offered by the question.

tracks the plane's speed

plane's speed relative to what? Relative to the conveyor? Airspeed, relative to the surrounding air?

The plane's speed relative to anything but the air is irrelevant to lift. The conveyor system can track whatever it wants and move the conveyor at any speed forward or backward. It wouldn't matter because the plane freewheels over its surface and propels itself by pushing static air.

If it's airspeed, the very point at which the plane breaks the hold (There is no hold - nothing attaches the plane to the conveyor) and theoretically begins to move, the conveyor would be moving it backwards (How? nothing attaches the plane to the conveyor) and the wheels would never rotate and the plane would remain stationary. (The wheels would roll but their rotation is irrelevant - they don't move or drive the plane) The plane is not being held stationary by any physical force, it's being held by the question. (False, the question does not create a scenario of zero velocity.) You have to assume that the plane starts to move and rotate the tires for the plane to gain airspeed. (Not so. the wheels are irrelevant except as a friction reducer between the plane and runway ... the same outcome would hold if it were a seaplane on pontoons over an ocean current, or on skis over a moving ice floe. Besides, if the conveyor followed the plane, the wheels wouldn't move either, but the plane would nonetheless move forward through the air, creating lift.) Well the question limits this assumption because one can make an assumption that allows for a different answer, therefore the question is flawed in that it allows for a yes and an no answer. (The assumption you say I "have to assume" is based on a false premise - the premise that the motion of a conveyor belt under a freewheeling air-powered vehicle can affect its linear motion)

If you can't see the simplicity of logic. I can't help further. (Right back at you, brother )

You have to go and make it "fit" into

One more analogy and I'm done ...

Imagine a moving sidewalk like those at the airport. If you walk in the direction of the movement, you travel at double your walking speed relative to the windows next to you. If you walk in the opposite direction, you remain stationary relative to the windows.

Why? Because the source of your motion is your feet pushing on the on the walkway thanks to friction.

Now, put on a pair of roller skates. I'll walk next to the moving sidewalk and pull you onto it with a rope. No matter what direction we take on the sidewalk, you will travel at the speed I'm walking. If we travel with the sidewalk, your wheels won't roll, because I'm walking as fast as the sidewalk. If we travel against it, the wheels will roll twice as fast as if I was pulling you over the carpet.

Why? Because the source of your motion is no longer your own feet "attached" to the conveyor through friction ... it comes from my feet exerting force on the stationary floor next to you while you freewheel on your skates.

Or if you like, I'll tie the rope to the wall and you can haul yourself up the rope towards me. The source of your motion is no longer me, it's you ... exerting force on the rope connected to the stationary wall. The moving sidewalk can speed up, slow down or stop, but it doesn't matter. Your motion relative to the windows next to you depends on your arms pulling the static medium of the rope tied to the wall while your skates freewheel below you.

Likewise, an airplane exerts its force directly on the static air around it ... not on the ground. The conveyor under the wheels can do what it wants (regardless of the sensors or relative speed) because the plane's engines are acting on the air while the tires freewheel below it. The plane's motion relative to the air around it depends on its engines pushing the wing through the static air, thus creating airflow and lift.

Consequently, the plane absolutely can take off within the parameters of this question as stated.

Have a nice day and thanks for the brainteaser. This was great!