Long rod question

The question itself requires nit picking. If you pushed a rod 10 miles long you would barely be able to measure the difference in time from the front to the back moving...
 
mark1 said:
Think of a car on a treadmill driving forwards at the same speed as the treadmill is moving backwards. It will not go anywhere.

Now take that car, stick it in neutral so the wheels are free wheeling and therefore are providing no forward force. Now stick a big propeller and wings on the car. Now the propeller is providing the thrust. As the wheel are in neutral, they will just spin with the treadmill, with the prop pushing the car forwards. It doesn't matter how fast the treadmill moves, as the wheels are free wheeling they are providing no backwards force (ignoring the small friction they create) and so the plane will move relative to the air and thus create lift.

I'm waiting for it to click :p

EDIT: Damn fast moving threads.
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Im not sure where this thread is going. But I dont see how this is difficult to grasp. If the car is freewheeling it's akin to being levitated so any adidtional thrust from a propeller will push it forward providing there is enough inertia.
 
I'm actually grateful of this thread, despite my mild humiliation, it's been quite enlightening.


(EDIT\\ and 1 last thing, i still insist the myth busters experiment was a load of tosh! :p)
 
Le_Petit_Lapin said:
Blow air from the BACK and the plane stays on the ground.

Blow air from the front and you're only giving it a hand in this case, it'll go up, as its getting air over its wings, but wont move its position on the ground.



:facepalm:

.....and we're back to step one. I'm not a plane, and dont have the benefit of engines that push against air.
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Actually, I'm not sure about that first part. Does a wing generate lift if air goes over it from behind? I feel it probably does, but in an uncontroled and unpredictable way due to turbulence.

The issue is about takeoff, ie leaving the ground,, not travelling forward while in the air.

Sigh

Engines don't push against air. People used to think travel to the moon would be impossible because the rockets would have nothing to thrust against.

If you strap on wings and run you are a plane up to the point of take off because you are doing the same thing - getting up speed so that the split airflow across your wing can generate lift. Once you take off and get into into the air you will soar into the sky like a brick - or to put it another way your legs will not maintain your airspeed and you will lose your lift and fall back to earth.
 
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Le_Petit_Lapin said:
Blow air from the BACK and the plane stays on the ground.

Blow air from the front and you're only giving it a hand in this case, it'll go up, as its getting air over its wings, but wont move its position on the ground.



:facepalm:

I'm unfortunately not a plane, and don't generate motion like a plane would.
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Well, ignoring the somewhat rude and intolerant facepalm, in my strap on wing and gym scenario you are a plane and you do generate motion and lift in EXACTLY the same way up to the moment after take off. :)
 
Katoom said:
To the OP. If you assume that it can't stretch, then it shouldn't compress either, then it should be instant.
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If you assume it can't stretch or compress at all then such a material does not, or can not ever exist in this universe. It would violate a whole bunch of scientific laws/theories, relativity especially
 
EffBee said:
Well, ignoring the somewhat rude and intolerant facepalm, in my strap on wing and gym scenario you are a plane and you do generate motion and lift in EXACTLY the same way up to the moment after take off. :)
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No, you don't.

You generate motion by, shoving your feet against the ground.

Planes on the other hand shove their props/jets against air.

EffBee said:
Sorry, I am assuming jet engines. You must be imagining airscrews (propellors).
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Jets are the same, all they do is "Suck, Squeeze, Burn and Blow."

Air gets shoved out backwards, plane gets shoved forwards in reaction.
 
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EffBee said:
Sorry, I am assuming jet engines. You must be imagining airscrews (propellors).
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They both work in exactly the same way...

A prop/turbine blade turns and deflects air in a given direction. The only thing that changes is the way in which the rotational motion is created.

You may be thinking of a rocket engine :confused:
 
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