Physics question.. can you figure it out?

[jpratt]

Where does it state in what relation it moves to? Does it say that it moves in relation to the static ground or the belt?

For the plane to move it has to push against the air. The plane starts to move forward so the belt begins to move backwards. That does not mean that the plane must stay stationary to the static ground. There is no violation of the stating rules. It says that the belt moves in opposite direction of the plane, that is all.

 

[jpratt]

Someone mentioned it earlier but I cannot find it now, this topic is on the Mythbuster discusion board now. http://community.discovery.com/groupee/forums/a/tpc/f/9701967776/m/7451937218/p/1

 

[BLACK6PACK]

1ARUNM,
The problem with your argument is that you're saying the plane is stationary. If that is the case then the conveyer belt would not be moving either, because the conveyer belt matches the speed of the plane.

The plane is sitting still as is the conveyer. The plane fires up its engines, and pushes in the throttle. The plane produces thrust therefor it starts moving forward at 1mph, at the same time the conveyer moves backwards at 1mph. The plane continues to accellerate up to 70mph as the conveyer accellerates up to 70mph in the opposite direction. The plane's tires are going 140mph. I just don't see how those that think it won't fly can't grasp this!

 

[83hurstguy]

Every scenario you "fly" guys have presented has involved the plane moving faster than the conveyor.

nope!!! plane speed is identical to the conveyor, the wheels are at a speed twice that of the conveyor.

You can forget all the thrust, physics rules, Newtons third law etc. to explain it except for wing aerodynamics. I'm not saying you can suspend the rules of physics but they are limited by the condition that the plane is rolling on the conveyor at the same speed opposite the conveyor belt. You are supposing things that aren't given in the original condition. It doesn't say whether the plane is an F-18 or the Wright flyer.

ummm.... Newtons third law is not limited by condition. Physics rules apply to every situation, and are implicit, whether the problem states them or not. Just b/c the problem doesn't explicitly say "the plane pushes on the atmosphere", it does. And it would make a difference if it was an F-18 or a Wright flyer, b/c I don't think the Wright flyer had wheels

If you were standing next to the conveyor as this happened, the plane would appear to be standing still with the wheels rolling on the conveyor as long as the conditions were met.

use those laws of physics you disregarded in the above paragraph to figure out why this statment is incorrect.

For it to move forward in relation to you and the air, it has to be moving faster than conveyor speed.

here's where the error starts... what is "it"? "It" is not the plane... use wheels in place of "it", and the statement become true.

It's clear in the original post that the opposite speeds neutralize each other and that is the limiting factor. The plane is not allowed to go faster than the conveyor, and therefore is not moving through the air and will not fly.

here is the biggest error. think about this (and read the last 4 pages of posts). Take a skateboard, hold it on a treadmill... does it HAVE to move backwards just b/c the wheels are rolling? NOPE. in fact, you can push it forward at a speed opposite that of the treadmill without any more effort than if the skateboard was sitting on a nonmoving surface.

 

[V6 Beast]

Every scenario you "fly" guys have presented has involved the plane moving faster than the conveyor. You can forget all the thrust, physics rules, Newtons third law etc. to explain it except for wing aerodynamics. I'm not saying you can suspend the rules of physics but they are limited by the condition that the plane is rolling on the conveyor at the same speed opposite the conveyor belt. You are supposing things that aren't given in the original condition. It doesn't say whether the plane is an F-18 or the Wright flyer.

The plane is moving forward at 200 mph.. how fast is your conveyer moving?

What you non-fly guys can't seem to grasp is the movement of the runway has very little affect the planes ability to move forward.

 

[1ARUNM]

The original question says equal speeds.

Speed is distance over time. If the plane moves across the belt to the left 1 foot in one second and stops where is it?? 1foot to the left.

OK now if the conveyor starts and moves one foot to the right in 1 second and stops where is the plane? Back where it started!!

Does anyone argue with that???

Now does it matter if these two events happen at the same time ??

I don't think so.

 

[jpratt]

1arunm, you are putting up a good fight but eventually you will see the way of the dark side.

 

[BLACK6PACK]

Its pretty simple. The conveyer moves to the left at 100 mph, the plane moves to the right at 100 mph. Is the plane stationary? NO its moving to the right at 100 mph. The planes wheels are moving 200 mph.

The plane would only remain stationary if the thrust put out by the prop or jet (lets say 400 lbs of thrust) was equal to the the drag caused by the wheels on the conveyer (400 lbs of drag). But if the plane is stationary, then the conveyer wouldn't be moving since it matches the speed of the plane.

 

[BLACK6PACK]

1ARUNM

Speed is time over distance. If the plane moves across the belt to the left 1 foot in one second and stops where is it?? 1foot to the left.

The problem with this argument is that when the conveyer moves to the right 1 foot, you assume that the planes wheels are locked and that it will move exactly one foot. If the plane's wheels are free wheeling then the plane may only move one inch. (an object at rest tends to stay at rest...) Its kinda like yanking a tablecloth from underneath all the dinnerware that is on top of the tablecloth.

 

[83hurstguy]

Speed is distance over time. If the plane moves across the belt to the left 1 foot in one second and stops where is it?? 1foot to the left.

If you wanna get technical, speed is the magnitude of velocity. If the plane moves to the left one foot and stops, it is one foot to the left, here, you are correct.

OK now if the conveyor starts and moves one foot to the right in 1 second and stops where is the plane? Back where it started!! Does anyone argue with that???

This is not necessarily true. Your statement assumes that there is a DIRECT LINK between the conveyor and the aircraft (the aircraft body is 'laying' on the conveyor). Tie the aircraft to a tree next to the runway and move the conveyor backwards one foot... aircraft goes nowhere b/c the wheels spin.

Here, you are making assumptions not listed in the problem (like you accused us of doing). The original problem in NO WAY states that there is a "direct link" between the aircraft body and the runway other than the contact through its tires.

Go back to your treadmill with a skateboard on it. Leave the treadmill off. Push up the skateboard a foot. There is your first statement... the "plane" moved a foot. Hold the skateboard and turn the treadmill on so the belt moves back a foot... no skateboard motion!!! This condradicts your second statement. The thrust from the jet engine acts like your hand does, independent of the conveyors motion.

 

[1ARUNM]

I understand what you guys are saying The question is not very clear as to what the speed is in relation to, conveyor belt or air speed, but it does say at the same time. Since the plane is on the conveyor belt it seems it has to travel across the belt to move which could be defined as distance.
If travel across the belt only is not considered speed it won't fly.

If the conveyor and the plane started off at exactly the same time and the wheels and belt were moving in opposite directions at the same speed, the plane would not have any speed.


You can make logical arguments for both sides of this, but if no one took up for the opposing side it wouldn't be any fun.

I still think I should have been on the debate team

 

[BLACK6PACK]

I like to debate things too. Its a good way to learn and see both sides of an argument. I never really wanted to be on a debate team because I think I'd be a master at it, and I never really wanted to be known as a masterdebater!

 

[87 Pete]

How can an airplane fly if there is no airflow over the wings?

As stated, it seems to me that the ONLY thing moving is the conveyor belt. As such, the airplane is standing still relative to the ground and therefore no air is flowing over the wings and it the wings will create no lift.

If you tried to fly an airplane off of stationary runway on the moon, you could never take-off because there is no air in space, and the wings need airflow to make low pressure over the top of the wing to create lift.

My .02 cents...

Pete

 

[rtviper]

Like I said earlier the thrust from the engines will stop the plane from moving backwards with the conveyer belt. If the belt is trying to match the planes speed it will only require more thrust to achieve a given speed then normal because of the conveyer belts movement and the friction of the wheel. Dont forget the belt is trying to match the planes speed from a dead stop. So at 20 mph the belt will move at 20 mph at this point or less the belt will never be able to overcome the thrust from the motors. Hold a skateboard on a treadmill as its is moving and it will take some force from your hand then apply more speed to the treadmill and you will still be able to move the board froward with just a little more effort. The resistance is from the wheel bearings as the wheels turn and thats not near enough to prevent forward motion. Now apply 4 engines with 59000 lbs thrust each and bye bye plane

 

[turbobuickman]

I just ran out of ways to explain this. The plane WILL take off. End of story. Read the last 4 pages and think about it. If all you nay-sayers are just arguing for the sake of arguing I think its over.

On a side note, this WAS a great thread for the first few pages. How about a different riddle for the cunning linguists and master debators among us?

 

[rtviper]

Here is an explanation that the doubters have to understand. The plane is on the conveyer belt and one of those small electric carts that pull the planes around is hooked to the nose of the plane with a chain. The cart pulls the plane at 20 mph and the belt speeds up to 20 mph. Now the power from the cart is similar to the thrust of the engines, it is no way intertwined with the belt. You must believe the plane will still move forward as the cart continues to pull. The wheels will be turning at 40 mph or so but the plane will follow the cart. It wouldnt matter if the cart was pushing the plane from the rear as long as we understand the cart is not on the belt also. The thrust from the motors is the same force a 1000 times

 

[turbot2496]

I understand what you guys are saying The question is not very clear as to what the speed is in relation to, conveyor belt or air speed, but it does say at the same time. Since the plane is on the conveyor belt it seems it has to travel across the belt to move which could be defined as distance.
If travel across the belt only is not considered speed it won't fly.

If the conveyor and the plane started off at exactly the same time and the wheels and belt were moving in opposite directions at the same speed, the plane would not have any speed.


You can make logical arguments for both sides of this, but if no one took up for the opposing side it wouldn't be any fun.

I still think I should have been on the debate team

Jesus frickin christ man .... this is not that frickin difficult... the speed of the conveyor belt doesn't even matter...the planes wheels are free wheeling.... use your head instead of trying to think up ways to prove up is down...its been explained to you every which way ... put the keyboard down step back and think about it and quit embarrassing yourself

 

[jpratt]

Be nice. It was meant to bring up a debate. Just becuse someone doesnt think like you do is not that bad. They will see the light someday.

 

[turbot2496]

Yeah I know... This thing keeps dinging my email and I'm just amazed that some still don't get it.... apologies... :wink: carry on...

 

[KEVINS]

Here is an explanation that the doubters have to understand. The plane is on the conveyer belt and one of those small electric carts that pull the planes around is hooked to the nose of the plane with a chain. The cart pulls the plane at 20 mph and the belt speeds up to 20 mph. Now the power from the cart is similar to the thrust of the engines, it is no way intertwined with the belt. You must believe the plane will still move forward as the cart continues to pull. The wheels will be turning at 40 mph or so but the plane will follow the cart. It wouldnt matter if the cart was pushing the plane from the rear as long as we understand the cart is not on the belt also. The thrust from the motors is the same force a 1000 times

This theory doesn't work because you have a source outside the "Working System" relative to the movement of the plane and belt. Put that cart on the belt with a chain to the plane THEN you have the cart "inside" the Working System and the plane will NOT fly.

ks