A jet plane on a large treadmill

[P_McPoser]

Pechelman, get some rockets and get your ass up here to my clubhouse. We need to get scientific n' shit.

[AsheanMT]

the treadmill will be spinning at the same speed as the tires

[Powow]

the treadmill will be spinning at the same speed as the tires

No, it doesn't. The treadmill moves at the same speed at the plane. Ignore the tires completely, all that needs to be there is something that allows the plane to move freely forwards with respect to the treadmill, like wheels, skids, maybe it hovers on magnets like those new trains. whatever, it doesn't matter.

[pechelman]

either im 100% right, or I dont get it

the turbine applies force to the mass of the plane to make it move
the plane weighs a lot, so that turbine force sees a lot of resistance

since it sees a lot of resistance, the plane accelerates relatively slowly
which in iteself is irrelavant, because the treadmill matches this speed instantly.

im still not seeing how one rationalizes that the plane has relative velocity to anything.

edit: anything related to the earth as a reference frame. lets not get all astronomical here.

[P_McPoser]

uber simplified FBD showing no forces being placed directly opposite those of the engines by the conveyor.

[Powow]

since it sees a lot of resistance, the plane accelerates relatively slowly
which in iteself is irrelavant, because the treadmill matches this speed instantly.

It matches the speed, but then what does that mean? The treadmill doesn't put any force on the plane.

[focus]

gah
thrust has nothing to do with it, other than it gets the plane to a specific airspeed.

that analogy doesnt help MeatPuppet.

If ConveryVelocity = Plane Velocity then shits not moving anywhere except the air through the turbines...which as I said, is not a sufficient force to accelerate the plane to takeoff airspeed velocity in the time the plane would hit the ground if it dropped its landing gear.

pechelman! Pay attention! Plane velocity is not measured by how fast the wheels are spinning. Plane velocity is measured by how far the plane actually travels in a given period of time. If "shits not moving anywhere," the conveyor belt, by the very fucking premise of the question, is not moving.

[P_McPoser]

either im 100% right, or I dont get it

the turbine applies force to the mass of the plane to make it move
the plane weighs a lot, so that turbine force sees a lot of resistance

since it sees a lot of resistance, the plane accelerates relatively slowly
which in iteself is irrelavant, because the treadmill matches this speed instantly.

im still not seeing how one rationalizes that the plane has relative velocity to anything.

It's all about the interaction of the conveyer at the wheels. The energy goes into turning the wheels, on the free pivot, rather than creating any vector that counteracts the thrust.

[DJSapp]

Heres how I read the problem

Plane is standing still on the treadmill to start, with 0 air and ground speed.
Plane fires its turbines and instantly, the treadmill matches to maintain this 0 velocity condition.

Wrong. Motherfucking wrong.

The plane fires its engines, which push against the air and the plane starts moving at 1 mph. The treadmill begins moving at 1 mph BECAUSE THE FUCKING TREADMILL MATCHES THE FUCKING PLANES SPEED. PERIOD. Please reread the question until you understand this.

The force from the treadmill cannot push the plane backward since the wheels do not transfer energy to the airplane.

[focus]

the treadmill will be spinning at the same speed as the tires

except the treadmill is not moving forwards, and the plane (which is attached to the tires) IS moving forwards.

[P_McPoser]

Wrong. Motherfucking wrong.

The plane fires its engines, which push against the air and the plane starts moving at 1 mph. The treadmill begins moving at 1 mph BECAUSE THE FUCKING TREADMILL MATCHES THE FUCKING PLANES SPEED. PERIOD. Please reread the question until you understand this.

The force from the treadmill cannot push the plane backward since the wheels do not transfer energy to the airplane.

Ok Pechelman, two fellow enginerds just typed almost the exact same posts. Are you a beleiver yet?

[focus]

The force from the treadmill cannot push the plane backward since the wheels do not transfer energy to the airplane.

A car would move forwards on this same treadmill. What's with all this free pivot nonsense???? Has absolutely nothing to do with the problem or the solution to the problem. You fucking engineers are overanalyzing schitt and getting yourselves confused.

[AsheanMT]

except the treadmill is not moving forwards, and the plane (which is attached to the tires) IS moving forwards.

Correct. The plane IS moving forward and WILL takeoff!

[focus]

Correct. The plane IS moving forward and WILL takeoff!

....and the wheels will be spinning at twice the speed of the treadmill.

[P_McPoser]

A car would move forwards on this same treadmill.

That's why dyno shops are so fucking dangerous. Always cars jumping off those fucking things smashing through walls n' shit!!

[AsheanMT]

how bout this.....

if all those who say no fly are the treadmill
and all those who say will fly are the wheels of the plane
then this thread would be the plane just after takeoff

[pechelman]

the thrust is counteracted by the plane's mass.
the problem says the plane and treadmill's velocities are equal, which in my mind, means the plane doesnt move.
nothing that has been so far has made me understand what you guys are saying (right or wrong).

and focus, give me a break.......
I know how a plane's velocity is measured.
Its called a pitot tube.
It measures the different in incident airflow pressure vs ambient pressure.
This difference in pressure is then used to calculate a velocity.

[AsheanMT]

....and the wheels will be spinning at twice the speed of the treadmill.

Yes!! Yaaaaaa, you're not a dumbshit!!

[focus]

That's why dyno shops are so fucking dangerous. Always cars jumping off those fucking things smashing through walls n' shit!!

You fucking idiot -- the treadmill doesn't move backwards unless the car moves forwards. The speedometer will show a speed of 40mph when the car is actually going 20mph (relative to the earth).

But yeah, keep rolling your eyes. Reread the question and report back.

[f2f]

group photo of everyone who posted in this thread:

[AsheanMT]

group photo of everyone who posted in this thread:

I'm the handsome fella in the back row all the way on the right

[DJSapp]

the problem says the plane and treadmill's velocities are equal, which in my mind, means the plane doesnt move.
nothing that has been so far has made me understand what you guys are saying (right or wrong).

Velocity is not force. There is an unbalanced force acting on the airplane. The force from the engines is much greater than the friction from the wheels.

Newtons first law states that an object at rest will remain at rest unless an unbalanced force acts upon it.

F=MA

Since the plane has an unbalanced force acting upon it, the plane will accelerate.

edited for quote clearity

[P_McPoser]

the thrust is counteracted by the plane's mass.

This is not possible without a force acting opposite the thrust. F=MA. You've got the M, but no A, only A is being created by the engines. You're stuck on overcoming the inertia, but it is overcome instantly, or else the wheels or conveyer wouldn't start to turn at all.

[focus]

the thrust is counteracted by the plane's mass.
the problem says the plane and treadmill's velocities are equal, which in my mind, means the plane doesnt move.
nothing that has been so far has made me understand what you guys are saying (right or wrong).

and focus, give me a break.......
I know how a plane's velocity is measured.
Its called a pitot tube.
It measures the different in incident airflow pressure vs ambient pressure.
This difference in pressure is then used to calculate a velocity.

No, that's how you estimate the plane's velocity. Next time you're driving on an icy road, floor the gas pedal. The speedometer needle will jump, but that doesn't mean the car's actually going that speed. A speedometer is a tool used to estimate a car's velocity -- similar to your pitot tube.

Velocity is, by definition, the distance traveled by some unit of time. Velocity has absofuckingloooootely nothing to do with incident airflow pressure, ambient pressure, or wheel speed.

You're having a bad thinking day -- it's ok. Just don't ask for any more breaks.

[AsheanMT]

Fuck This, I'm gonna go skiing. I'll check on you tards later.