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Started By
Message
re: Can this 747 take off?
Posted on 4/13/24 at 10:35 pm to doliss
Posted on 4/13/24 at 10:35 pm to doliss
quote:
And adding thrust as a forward vector does not count
but it does
quote:
If the forward vector from engine thrust is combined with the equal vector in the opposite direction from the treadmill motion then the net vector is 0
The thrust from the engine and the motion from the treadmill in the opposite direction arent equal though. Thats where you are messing up. The treadmill and the free spinning wheels cancel out allowing the forward thrust from the engines to prevail.
Someone earlier in the thread had a good analogy. If you are on a skateboard on a treadmill, the wheel speed will always equal the treadmill speed and you will stay stationary. If someone hands you a rope while you are on the skateboard, can you pull yourself forward? Of course you can. In that example your arms are the engines/ props and the rope is the air.
quote:
No it can’t. The wheels are the only thing moving in place and there’s no air going over the wings.
Youre wrong too
This post was edited on 4/13/24 at 10:37 pm
1
Posted on 4/13/24 at 10:42 pm to highcotton2
quote:
How does a free spinning wheel hold back a jet engine?
The wheels are only moving because the thrust pushes the plane forward. If the treadmill offsets that forward motion by moving in the opposite direction at the same rate of motion then the plane does not move forward. Its the same reason people don't move forward on a treadmill while running if they are going the same speed as the treadmill
Posted on 4/13/24 at 11:00 pm to im4LSU
quote:
The thrust from the engine and the motion from the treadmill in the opposite direction arent equal though. Thats where you are messing up. The treadmill and the free spinning wheels cancel out allowing the forward thrust from the engines to prevail.
The only reason the wheels are moving is because the thrust moves the plane forward. The treadmill matches that forward movement equally but in the opposite direction. That means the plane does not move anywhere.
The riddle says it matches the speed of the wheels, which is why there is no forward movement. The speed of the wheels are what move the plane forward relative to the ground. If the "ground" moves in response to that wheel movement then the plane can't move along the ground and therefore never generate lift from the wings.
The analogy of the rope and skateboard does not work because the plane and treadmill are a closed system and the rope is applying a force outside of the system
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