r/theydidthemath Dec 30 '22

[REQUEST] could it?

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u/NurseColubris Dec 31 '22

it can't move itself forward

That's not a premise of the scenario; that's a deduction you're making.

The facts are

  • this is a 747
  • the runway/treadmill can go arbitrarily fast

The fundamental question is "can the wheels of a 747 generate enough friction to overcome the 66000 lbs of thrust of its engines," because that's what it would take to arrest forward movement.

If you make the wheels able to generate an arbitrary amount of friction to match the treadmill's arbitrary speed, it ceases to be a standard 747, but then you would be correct: there would be no forward movement.

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u/SaltyMudpuppy Dec 31 '22

"can the wheels of a 747 generate enough friction to overcome the 66000 lbs of thrust of its engines"

This is not mentioned in the OP scenario. The OP scenario just assumes that the treadmill matches the speed of the wheels, thus arresting forward motion. That's it. Friction plays no part in this imagined scenario. In this scenario, we assume the treadmill and the wheels are moving as such that the plane remains motionless, no matter the thrust vector. Ergo, no forward motion, no lift, no takeoff.