A jet plane on a large treadmill

[Tippster]

We all explode?

TELL ME!

[Roo]

Soylent green is treadmills!

[skinny_kid]

I just talked to a dude with a BS in Physics from Boston U, he is smart, he says no

[Roo]

I just talked to a dude with a BS in Physics from Boston U, he is smart, he says no

If you think he's smart, you must be catastrophically dull.

[philippeR]

If you think he's smart, you must be catastrophically dull.

I've just spit coffee all over my keyboard. Thank you.

[Tippster]

If you think he's smart, you must be catastrophically dull.

Stop making me draw attention to myself in our newsroom.

[focus]

We all explode?

TELL ME!

Your left hand moves backwards at the exact same speed, which, because of the dowel rod, really has little to do with the right hand.

edit: page 20, here we come...

edit edit: the dowel rod really isn't important either, actually.

[skinny_kid]

I just got owned

[Tippster]

But I know something you don't know..... I am not left-handed!

[DJSapp]

You still don't get it.

This is, actually, according to you as well. What you don't seem to get is that the treadmill can only accelerate to the speed of light if the airplane accelerates to the speed of light in the opposite direction. I'm pretty sure that takeoff speed < the speed of light. It doesn't matter that the maximum frictional force < thrust. That is an entirely different discussion.

You didn't pick apart shit, man. Not to fight w/ you or anything. With that post, you're the last one who should talk about faulty logic.

Focus, stop, breathe. I'm on your side. The plane takes off. Hell, I probably have 50 posts in here stating this. Since explaining the correct forces and motion involved with the problem has not convinced people, I resorted to using their own flawed arguments against them. That post was specifically directed at the people who believe the treadmill can move at a velocity fast enough to create a frictional force great enough to counter the airplane's thrust (i.e. zero net force).

What I was getting at in that last post was the people who (incorrectly) believe the treadmill speed is linked to the wheel rotation speed. This is the faulty logic I was refering to, since you cannot change references between airframe speed and wheel speed in the middle of the problem. I ran with their incorrect assumption to calculate the frictional losses due to the treadmill rotating at the speed of light (also incorrect due to the rules stated in the problem). For the plane to remain stationary, there must be no net force. This is Newtonian physics. I proved even through all of these incorrect assumptions about the problem that the plane has a net forward force, and will fly.

[PearlJam09]

Its simple bernoulli principle. The same reason why a frisbee flies. The shape of the wing causes the air going over the top to go faster, thus lowering the pressure. This pressure difference causes force to be applied to the underside of the wing, creating lift. If there is no air going past the wing, there is no lift. This plane cannot, will not ever take off.

[MeatPuppet]

Its simple bernoulli principle. The same reason why a frisbee flies. The shape of the wing causes the air going over the top to go faster, thus lowering the pressure. This pressure difference causes force to be applied to the underside of the wing, creating lift. If there is no air going past the wing, there is no lift. This plane cannot, will not ever take off.

Well, that should settle it.

[focus]

Focus, stop, breathe. I'm on your side.

Ok. I missed the transition between you talking about forces and inertias and the airplane pushing against the air instead of its wheels (like it mattered) and all that other bullshit and then talking about the same thing that I was talking about.

My bad.

[dbp]

Its simple bernoulli principle. The same reason why a frisbee flies. The shape of the wing causes the air going over the top to go faster, thus lowering the pressure. This pressure difference causes force to be applied to the underside of the wing, creating lift. If there is no air going past the wing, there is no lift. This plane cannot, will not ever take off.

Everybody on both sides of the discussion knows what makes a plane fly. The people who think the plane will take off believe the treadmill can't keep the plane from moving forward and creating airflow.

[focus]

Everybody on both sides of the discussion knows what makes a plane fly. The people who think the plane will take off believe the treadmill can't keep the plane from moving forward and creating airflow.

and then there are the few who realize that the treadmill doesn't care if the plane moves forward or not, it isn't trying to do anything but spin backwards at the same speed the plane is going forwards. That Cecil guy didn't seem to get it either.

[Brock Landers]

I think I may be moving over to the fly side.
Its not real easy to figure though, so everyone calling everyone else an idiot for whatever theyri reasoning is isnt making much sense either. Its a complicated problem and Im still not so sure.

Everyone knows what makes an airplane fly- need air flow (or low pressure above the wing relative to the bottom). Thats fine everyone agrees.

The only thing people arent agreeing on is if the plane is moving forward (for some this whole post will be really redundant but Im trying to sort it out for everyone).

There are 4 forces in aerodynamics- thrust, drag, lift, and gravity.

For our purposes we can see that the legs/wheels of the plane are taking care of the lift AT THIS POINT WHILE ITS ON THE TREADMILL.
The opposing force is gravity, which is pulling the plane down. Here we have the equal and opposite reactions keeping the plane where it is (i.e. not going up or down)

The thrust is the jet engines pushing the plane forward. The drag is the air resistance (AND the treadmill, to a degree- Ill get to this later). For those who say the plane wont move forward, its because of the treadmill making the relative forward movement 0 right? The thrust is independent of the treadmill. The treadmill will spin the wheels in the direction it is moving but the plane, an independent system relative to the wheels, will continue forward.
If you put a plane on a giant ice rink (or a fucking frozen lake) and shot the engines off, it would move forward, despite no reaction between the wheels and the surface. The wheels are independent of the engines and forward motion. The wheels only hold it up in place.
So, I would say that the plane could move forward. My only thing is that THERE IS FRICTION in this world- otherwise...whatever. This all assumes a frictionless scenario which is stupid and hypothetical because without friction there isnt lift/drag/whatever anyway.
This friction is going to have some backward affect on the plane, between the wheels spinning etc, so Im just saying while it can move forwardusing the thrust of the engines, itll require a lot more power and Im not sure a plane can exert enough extra force to get it off the ground (to move forward fast enough-realistically). This is what I meant by the drag also being part of the wheels. Of course, if the plane CAN overcome this extra drag (using extra thrust) it will fly. Once in the air itll have normal drag.
Sorry for the apparent flip flop

[DJSapp]

Brock,

You got it, and to help clearify:

Rotational friction is independant of speed. The treadmill could be going the speed of light and would exert the same frictional force as regular ground. This is a common high school physics experiment where you drag a skateboard around with a load of bricks on it at different speeds and measure the tension on the spring. Friction does not increase with speed.

[Brock Landers]

Brock,

You got it, and to help clearify:

Rotational friction is independant of speed. The treadmill could be going the speed of light and would exert the same frictional force as regular ground. This is a common high school physics experiment where you drag a skateboard around with a load of bricks on it at different speeds and measure the tension on the spring. Friction does not increase with speed.

Yup, Im just thinking the mass (Normal Force) of the plane will affect the friction force just in terms of sheer magnitude, and the thrust of a normal plane may not be able to overcome this enough to fly. It may be able to as well- I majored in physics, not aerospace engineering, and dont know the force needed to fly compared with mass.

[DJSapp]

Yup, Im just thinking the mass (Normal Force) of the plane will affect the friction force just in terms of sheer magnitude, and the thrust of a normal plane may not be able to overcome this enough to fly. It may be able to as well- I majored in physics, not aerospace engineering, and dont know the force needed to fly compared with mass.

Wait, hang on. The treadmill doesn't make the plane heavier.

Rotational friction = u * M * g / r

Airplanes overcome this every day. This isn't aerospace engineering.

[Brock Landers]

Youre right, it just seems like the friction at the wheels would be a little greater with the treadmill going in the other direction right? Maybe not, Im still thinking it moves forward...my friction thoughts are based more on intuition I guess which gets physical mechanics screwed up anyway

[DJSapp]

Youre right, it just seems like the friction at the wheels would be a little greater with the treadmill going in the other direction right? Maybe not, Im still thinking it moves forward...my friction thoughts are based more on intuition I guess which gets physical mechanics screwed up anyway

In the real world, it does. There's heat loss, fluid friction from the grease on the bearings, and lots of other tiny stuff. When compared to the 380,000 lbs. of thrust a 747 can generate, those losses don't matter.

[Brock Landers]

In the real world, it does. There's heat loss, fluid friction from the grease on the bearings, and lots of other tiny stuff. When compared to the 380,000 lbs. of thrust a 747 can generate, those losses don't matter.

Sounds good, I didnt know how much extra "doesnt matter" stuff a plane taking off could take. I know theres a ton of thrust needed just to get it off the ground but it looks like theres enough to overcome this extra stuff, thanks for the insight/help/whatever

[summit]

As I point out in the other thread, the speed required by the treadmill based upon those small difference to get enough frictino to hold the plane stationary (in the dubious supertreadmill interpreation) would result in enough treadmill interaction with the air that it would probably generate wind... which would generate lift... which would decrease the normal force... which makes the treadmill go waaay faster... and then the plane takes off (assuming no mechanical failure of the wheels/tires/treadmill)

plane might stall when it gets out of the generated wind ground effect area if it doesnt accelerate enough... but it will take off!

ETA the lower the aircraft's takeoff speed (lighter the weight) the sooner it happens
ETA if you switch to another aircraft whose wings are lower to the ground, you get a more significant wind effect sooner too

[Brock Landers]

As I point out in the other thread, the speed required by the treadmill based upon those small difference to get enough frictino to hold the plane stationary (in the dubious supertreadmill interpreation) would result in enough treadmill interaction with the air that it would probably generate wind... which would generate lift... which would decrease the normal force... which makes the treadmill go waaay faster... and then the plane takes off (assuming no mechanical failure of the wheels/tires/treadmill)

plane might stall when it gets out of the generated wind effect area if it doesnt accelerate enough... but it will take off!

I see your point, I just dont think even at ridiculous speeds would the treadmill cause enough wind/airflow over and under the wing to cause lift. Maybe though- Ive never been exposed to a supertreadmill first hand, this is just my "supertreadmill JONG" opinion. And not to nitpick, but itll only affect the net normal force- the normal force is always m x g, provided the m is normal to the ground. If the lift were to occur, it would increase lift, not decrease normal force... SEMANTICS, Im a nerd

[summit]

And not to nitpick, but itll only affect the net normal force- the normal force is always m x g, provided the m is normal to the ground. If the lift were to occur, it would increase lift, not decrease normal force... SEMANTICS, Im a nerd

isn't normal force the force thats exerted by the surface on the aircraft? i think N=m*g - F(lift)

anyways, friction forces become less