That's great! I'm not arguing that. The force is being exerted downward, and not forward or in reverse.... Downward force will not affect the desired end result of forward motion unless the downward force is so great that the plane won't move regardless of what's under it. We KNOW that this is not the case, otherwise there wouldn't be flight...

Try pushing your Xterra up a hill in neutral and then come back and ask again.

You're kidding, right?

And there you go....it's moving forward...

So what if you just have some really huge engines?

You need to think more abstractly

In the scenario you're describing, you're pushing vertically, not horizontally...

Assuming there is no wind, the plane has to move relative to the surrounding ground, i.e. whatever is next to the conveyor belt, to achieve flight. It's not going to do that if the conveyor is matching the aircraft's speed.

Yeah, but this scenario isn't on a hill. It's on a level runway.

OK. one more try. Kind of the opposite scenario posted by XPLORx4. Can we agree that one effect of the conveyor is to double the rotating speed of the wheels?

Imagine an aircraft on a long runway wtih a tailwind (FYI- a tailwind is counter-productive to the attainment of lift) of say, 120 knots. Exactly the airspeed needed by the aircraft to lift off. The aircraft begins takeoff roll, with the wind. The wheels spin faster and faster. The plane reaches 120 knots of groundspeed, and has reached zero airspeed. The aircraft continues to accelerate and reaches 180 knots groundspeed, which is 60 knots airspeed. The wheels are spinning at 180 knots now. The aircraft then reaches airspeed of 120 knots, which is 240 knots groundspeed, 240 knots of wheelspin. Lift can be achieved at 120 knots airspeed, and the plane takes off.

Those numbers in review:
At rest on the approach end:
Airspeed -120 [negative 120 knots]
Groundspeed 0
wheelspin 0

starting takeoff roll:
Airspeed 0
Groundspeed +120
wheelspin +120

Halfway to achieving lift:
Airspeed 60
groundspeed +180
wheelspin +180

at liftoff:
airspeed +120
groundspeed +240
wheelspin (before liftoff) +240

Now shouldn't the plane stay on the ground according to the "not-flyers'" logic?

Fine. Try pushing your Xterra on level ground and then ponder what weight has to do with forward motion. The force of gravity must be overcome to move an object, whether it's up, down, forward, back, or sideways.

The conveyor matching the airplane's speed will only cause the wheels AND the conveyor to rotate at twice the speed of the aircraft. Fact of the matter is the plane will STILL be moving forward regardless...

I'm becoming a PoHo thanks to this thread!

Ok...how has gravity come into play now? It's not going to prevent an airplane from taking off. If that were the case, we wouldn't have flight! See my first post on page 26

Uh, dude: Gravity only affects things in the VERTICAL dimension. You don't see apples fall from trees SIDEWAYS do you?

We are?

I guess you missed the equations:

See, this is what I'm saying. Your argument rides on a tailwind of fixed velocity. In the scenario, the conveyor moves faster and faster as engine thrust is increased, so the speed relative to the surrounding air remains zero.

If that's the case - the conveyor is no longer matching the speed of the aircraft.

AAARGGG!

The belt only moves if the plane moves....

Speed, or Movement, means relative to the world...not the belt.

My GPS will say I'm going 0 mph if I am on a tread mill that is turning at 4 mph.

If my tread mill MATCHES MY SPEED, it would be turning at ZERO MPH.

(I think Moby and BlueSky still think the earth is flat, btw...)

There's a new invention in town.

They call it the wheel!

It rolls, even on conveyor belts!

Actually, the wheel bearings are there to make it a nearly frictionless scenario

We tried to explain that to them but they are two busy defending the incorrect answer to read!!

You mean it's not flat?!? Prove it!! It has to be, otherwise we wouldn't be able to see a straight line on the horizon!