Bench > OHP

[ChaseT.]

 

[Barut]

Only because of the friction.

If you stop the skate from moving back with a gentle nudge of the hand it with remain stationary on the treadmill. This will overcome the initial friction that causes the skate to move.

 

[ChaseT.]

 

[takeahnase]

Shoot a lubricated rocket over a conveyor belt moving in the opposite direction with arbitraty speed? You think the rocket is going to slow down? If yes, why?

 

[hunto]

This is the right answer.

The toy car analogy is flawed. The wheels don't even have bearings. They don't spin freely at treadmill speeds.

Try the same thing with a skateboard or a good roller skate.

LOL

In a hypothetical question, we ignore practical questions of wheel bearing limits, etc- what belt can spin 600 mph, the top speed of a 747?

Friction is not the force that moves or keeps the plane still. Its the fact that the two forces acting on the airplane aren't in the same plane.

 

[takeahnase]

If you stop the skate from moving back with a gentle nudge of the hand it with remain stationary on the treadmill. This will overcome the initial friction that causes the skate to move.

Hence my rollerblade example.

 

[hunto]

Shoot a lubricated rocket over a conveyor belt moving in the opposite direction with arbitraty speed? You think the rocket is going to slow down? If yes, why?

I don't know waht this means.



Put on the skates, high-tech super-duper needle roller bearings. Get on the treamill. Tie a rope to the wall. Turn onthe treadmill. You must pull on the rope X amount to stay still, or the mill sends you the other way. Now speed up the mill. You must pull X+n, or harder, to stay still.

Becauase the forces aren't in the same plane.

 

[thethirddiaz]

I like Mythbusters, but that was shit. JPC's guy spelled it out much better.

 

[erco]

Take has it right.

The backwards motion of the treadmill will exert a very slight backwards pull on the plane. The translation of this force is minimal, but it's still there. In this little theory world we're living in with giant plane-sized treadmills, the treadmill will have to move at a ridiculous speed, many times greater than that of the air speed of the plane, in order for it to exert enough force that the bearings are able to translate it to the plane itself to keep it stationary.

 

[JPC]

The belt is NOT acting on the airplane. The wheels prevent that. If the landing gear got ripped off and the plane was laying on its belly on the ground, YOU WOULD HAVE A POINT.
Erco that was for hunto.

 

[bacon]

LOL at "lubricated rocket". I think they sell those in the back of Cosmopolitan magazine....

 

[Barut]

Hence my rollerblade example.

Yeah, I know.

Hunto, the bearings keep the two forces from acting on each other. The thrust of the propeller and the reverse speed of the belt move never act upon each other because the wheels spin freely.

If you have good luggage try this the next time your in an airport:

Walk along the moving side walk. To the side of it. Place your bag (if it has rollerblade wheels) on the walkway and drag it with you. It won't go faster than you walk. The fucking wheels are spinning freely. I promise.

 

[erco]

The belt is NOT acting on the airplane. The wheels prevent that. If the landing gear got ripped off and the plane was laying on its belly on the ground, YOU WOULD HAVE A POINT.

It is, but it's minimal. There's still friction. However, the question doesn't ask for the treadmill to move at a speed so as to keep the plane still. Instead, it asserts that the treadmill moves at a speed equal to the speed of the plane.

 

[hunto]

Lets say the thrust is one belt, moving right-to-left.
The plane is a ball, since we're concerned witht he wheels behavior.
The con belt is moving left-to-right.

If you spin the belts in the opposite direction, the ball stays in the same spot. Increase the speed of one belt, the ball moves relative to the belts. With me? If the belts are regulated to the same speed, the ball never moves, no matter how fast the belts spin.

The original question postulated that the con belt moves in direct response to the wheel speed of the plane.

 

[bacon]

If the landing gear got ripped off and the plane was laying on its belly on the ground, YOU WOULD HAVE A POINT.

*has a point*

 

[JPC]

I'm sorry I started this guys. I questioned Chase because I misunderstood the experiment.

 

[ChaseT.]

 

[ChaseT.]

 

[hunto]

Take has it right.

The backwards motion of the treadmill will exert a very slight backwards pull on the plane. The translation of this force is minimal, but it's still there. In this little theory world we're living in with giant plane-sized treadmills, the treadmill will have to move at a ridiculous speed, many times greater than that of the air speed of the plane, in order for it to exert enough force that the bearings are able to translate it to the plane itself to keep it stationary.

But that minimal force is there- and thats what we're talking about. Its a hypothetical question, and you hit the nail on the head. If the force exists, in theory, then its possible to hold the plane still. Remember we're talking hypo here, so belt limits, plane structural limits, etc, are out the window. And what we've distilled here is that there is a force acting on the plane against the direction of thrust. And in a hypothetical world, if we can make the belt match the forward speed of the airplane, the speed of the plane relative to the air around it, then yes, we can keep it on the ground.

 

[JPC]

Lets say the thrust is one belt, moving right-to-left.
The plane is a ball, since we're concerned witht he wheels behavior.
The con belt is moving left-to-right.

If you spin the belts in the opposite direction, the ball stays in the same spot. Increase the speed of one belt, the ball moves relative to the belts. With me? If the belts are regulated to the same speed, the ball never moves, no matter how fast the belts spin.

The original question postulated that the con belt moves in direct response to the wheel speed of the plane.

That analogy won't fit because the planes propellar is not acting on the wheels. The conveyor belt is. They are two different forces acting on two different things.