[quote]beebuddy wrote:
nephorm wrote:
beebuddy wrote:
In that case let’s give the plane frictionless bearings, in which case it would take off because the ground beneath might as well be “aether.”
Doesn’t it have to move fast enough relative to the air to generate lift?
Sure but with perfect bearings the action of the treadmill wouldn’t have any affect have on the plane, so the jet/prop thrust would pump the plane forward (relative to the atmosphere) even if the treadmill were blasting away at light speed.[/quote]
If we had treadmills that could move at the speed of light, why the fuck would we need planes?
[quote]Zap Branigan wrote:
beebuddy wrote:
nephorm wrote:
beebuddy wrote:
In that case let’s give the plane frictionless bearings, in which case it would take off because the ground beneath might as well be “aether.”
Doesn’t it have to move fast enough relative to the air to generate lift?
Sure but with perfect bearings the action of the treadmill wouldn’t have any affect have on the plane, so the jet/prop thrust would pump the plane forward (relative to the atmosphere) even if the treadmill were blasting away at light speed.
If you leave a skateboard on a treadmill will it be stationary or will it fly backwards?[/quote]
If the bearings are frictionless it just sits there.
I tried to edit away my post, because I thought about it immediately after, and realized I was incorrect. The thrust is propelling the plane forward regardless of what the wheels are doing.
I edited it almost immediately after posting it, so I am surprised it came back. Oh well.
[quote]Zap Branigan wrote:
If you leave a skateboard on a treadmill will it be stationary or will it fly backwards?[/quote]
But tie a rope to that skateboard, and pull it forward, and it doesn’t matter what the wheels or treadmill are doing… the skateboard will move forward. The wheels and the treadmill will spin infinitely fast, but that’s how the cookie crumbles.
[quote]Donut62 wrote:
Zap Branigan wrote:
beebuddy wrote:
nephorm wrote:
beebuddy wrote:
In that case let’s give the plane frictionless bearings, in which case it would take off because the ground beneath might as well be “aether.”
Doesn’t it have to move fast enough relative to the air to generate lift?
Sure but with perfect bearings the action of the treadmill wouldn’t have any affect have on the plane, so the jet/prop thrust would pump the plane forward (relative to the atmosphere) even if the treadmill were blasting away at light speed.
If you leave a skateboard on a treadmill will it be stationary or will it fly backwards?
If the bearings are frictionless it just sits there.[/quote]
You are correct sir. It might as well be floating.
[quote]nephorm wrote:
beebuddy wrote:
In that case let’s give the plane frictionless bearings, in which case it would take off because the ground beneath might as well be “aether.”
Doesn’t it have to move fast enough relative to the air to generate lift? [/quote]
That’s the point. People think in terms of cars, in which the wheels and forward motion are linked through a drivetrain. The engines of a plane are attached to the fuselage, and propel the plane through the atmosphere, not through a friction contact with the ground. The tires on a plane are merely free spinning and exert no force on the plane other than the inherent friction losses in the bearing assembly. It’s a trick question: The engines and wheels are in a different frame of reference. The force exerted by the wheel friction is so insignificant in relation to the thrust of the engines there is little impact.
EDIT: Sorry nephorm, I quoted you before the edit.
[quote]analog_kid wrote:
If we had treadmills that could move at the speed of light, why the fuck would we need planes?[/quote]
In order to join the mile-high club without visiting Denver.
[quote]Donut62 wrote:
EDIT: Sorry nephorm, I quoted you before the edit.[/quote]
Great, now my mistake is memorialized for future forumites to point and laugh.
Thanks a lot.
[quote]nephorm wrote:
Zap Branigan wrote:
If you leave a skateboard on a treadmill will it be stationary or will it fly backwards?
But tie a rope to that skateboard, and pull it forward, and it doesn’t matter what the wheels or treadmill are doing… the skateboard will move forward. The wheels and the treadmill will spin infinitely fast, but that’s how the cookie crumbles.[/quote]
Hahhaaa, this is the exact method our physics professor showed us this problem with. It was a toy car, though. You can hook the car up to a string tied to a spring force gauge to confirm that the only forces moving the toy car opposite to the direction you want to pull it is the calculated bearing friction.
[quote]nephorm wrote:
Zap Branigan wrote:
If you leave a skateboard on a treadmill will it be stationary or will it fly backwards?
But tie a rope to that skateboard, and pull it forward, and it doesn’t matter what the wheels or treadmill are doing… the skateboard will move forward. The wheels and the treadmill will spin infinitely fast, but that’s how the cookie crumbles.[/quote]
The planes engines act as the rope and this takes a certain amount of energy. The planes wheels are not frictionless so it is just a matter of having a powerful enough treadmill to keep the plane from moving forward.
[quote]Donut62 wrote:
nephorm wrote:
Zap Branigan wrote:
If you leave a skateboard on a treadmill will it be stationary or will it fly backwards?
But tie a rope to that skateboard, and pull it forward, and it doesn’t matter what the wheels or treadmill are doing… the skateboard will move forward. The wheels and the treadmill will spin infinitely fast, but that’s how the cookie crumbles.
Hahhaaa, this is the exact method our physics professor showed us this problem with. It was a toy car, though. You can hook the car up to a string tied to a spring force gauge to confirm that the only forces moving the toy car opposite to the direction you want to pull it is the calculated bearing friction.[/quote]
That is why you need a powerful treadmill to maximize the bearing friction and burn them out.
[quote]Zap Branigan wrote:
The planes engines act as the rope and this takes a certain amount of energy. The planes wheels are not frictionless so it is just a matter of having a powerful enough treadmill to keep the plane from moving forward.[/quote]
Lol, failplane. But if the treadmill gets uber bearings, why not give them to the plane too?
[photo]14294[/photo]
[quote]beebuddy wrote:
Zap Branigan wrote:
The planes engines act as the rope and this takes a certain amount of energy. The planes wheels are not frictionless so it is just a matter of having a powerful enough treadmill to keep the plane from moving forward.
Lol, failplane. But if the treadmill gets uber bearings, why not give them to the plane too?
[photo]14294[/photo] [/quote]
So now you want to test a plane that cannot be built as well as a treadmill that cannot be built?
[quote]Zap Branigan wrote:
Donut62 wrote:
nephorm wrote:
Zap Branigan wrote:
If you leave a skateboard on a treadmill will it be stationary or will it fly backwards?
But tie a rope to that skateboard, and pull it forward, and it doesn’t matter what the wheels or treadmill are doing… the skateboard will move forward. The wheels and the treadmill will spin infinitely fast, but that’s how the cookie crumbles.
Hahhaaa, this is the exact method our physics professor showed us this problem with. It was a toy car, though. You can hook the car up to a string tied to a spring force gauge to confirm that the only forces moving the toy car opposite to the direction you want to pull it is the calculated bearing friction.
That is why you need a powerful treadmill to maximize the bearing friction and burn them out.
[/quote]
OK, nevermind, I was confused. I was thinking of the plane bearings being frictionless, not the treadmill. In that case, treadmill pwns the plane.
[quote]Zap Branigan wrote:
beebuddy wrote:
Zap Branigan wrote:
The planes engines act as the rope and this takes a certain amount of energy. The planes wheels are not frictionless so it is just a matter of having a powerful enough treadmill to keep the plane from moving forward.
Lol, failplane. But if the treadmill gets uber bearings, why not give them to the plane too?
[photo]14294[/photo]
So now you want to test a plane that cannot be built as well as a treadmill that cannot be built?[/quote]
I get your point, but realistically we should probably assume that the technology used in the treadmill will have similar limitations to the technology in the plane.
Oooooo that’s tricky.
Yes, the blades just have to spin faster than the turn table. And they will.
If the table spins opposite the direction of the rotors, and at least has enough speed to cancel out the minimum rotation for lift, then no it won’t.
Holy shit…I need to get a life.
[quote]meangenes wrote:
Oooooo that’s tricky.
Yes, the blades just have to spin faster than the turn table. And they will.[/quote]
I think part of the thought experiment is to assume the turntable can go just as fast.
Would the helicopter engine need to run at all or could the pilot adjust the pitch of the blades to allow the rotation to cause it to lift off?