[meglamaniac]

Another example:

Imagine the plane has no engines and the treadmill moves forward, always at the required speed for takeoff. Would the plane ever take off? No. All that would be accelerating the plane would be the (minimal) friction from the wheel bearings. As soon as air resistance began to take effect that would be canceled out.

Now swap that around (so the minimal acceleration is now minimal deceleration) and the air resistance is now hugely negative (thrust from the engines)* instead of slightly positive and ask the question again: would the plane ever take off? Yes!



*I know this is not entirely clean as there is still forward air resistance but the engines are designed to overcome it, for obvious reasons.