Would the plane take off?

[nippinout]

In the probleme's set-up, the belt moves at the speed of the plane in the opposite direction. Plane goes 100mph, the belt moves at 100mph opposite to it. Read that again. The plane is going 100mph! The wheels are travelling at 200mph, but the plane is travelling at 100mph!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[neppo1345]

PWNED...ALL OF YOU

[UTDragun]

PWNED...ALL OF YOU

this link doesnt work

and here...

this one does

[nippinout]

I was under the impression that the conveyor belt exactly matched the plane's speed at all times... so it would be at a standstill although the wheels spin.

Try visualizing the treadmil example.

The wheels are not creating the forward movement of the plane, the engines pushing air is. The wheels are just spinning happily along due to the conveyor belt, while the engine is pushing the plane forward. Idealize the wheels as frictionless bearings. (For the love of god people, do not go into analyzing friction. Any engineer in the real world idealizes everything.)

[neppo1345]

works fine for me....

[nippinout]

I'm waiting for Mythbusters to test this and blow up a 747 in the process.

[SlartyBartFast]

But can the wheels support the extra speed? Or do they explode = plane doesn't take off?

[beam]

Here's my 2 cents.

The plane will take off. As long as the propulsion system is independent of the interaction with the ground, the ground has no effect.

Case in point: I can take off of an icy runway just as easily as a dry one. Why? My wheels don't "slip" because it is the prop that is pulling me forward. Now...stopping is another issue. My breaks are based at the wheels, stopping on ice is tough. Do you see?

[nippinout]

But can the wheels support the extra speed? Or do they explode = plane doesn't take off?

The question isn't whether or not the wheels/bearings/hydraulic fluid/brake fluid/rubber/tire pressure can handle the situation. Let's just assume nothing will break.

[beam]

Another thought to show the minimal impact of the moving runway: If the bearings in the wheels were perfectly frictionless [hey we're talking about a conveyor runway!], and the plane's engines were off, the plane still wouldn't move, the wheels would just spin. Now add the thrust of the engines an there you go. Acceleration and lift.

[nippinout]

Another thought to show the minimal impact of the moving runway: If the bearings in the wheels were perfectly frictionless [hey we're talking about a conveyor runway!], and the plane's engines were off, the plane still wouldn't move, the wheels would just spin. Now add the thrust of the engines an there you go. Acceleration and lift.

HIGH FIVE!!!

[nippinout]

Miscue, the conveyor belt isn't keeping the plane from moving. It is simply moving in a reverse direction from the plane. The wheels are spinning freely, sort of like isolating the plane from a moving or stationary runway.

[maxama10]

The plane is moving! Thrust from the engines moves air backwards, to propel the plane forwards. Equal and opposite... M1V1=M2V2

What happens at the wheels is not important! The engines produce forward thrust no matter what is going on with the wheels.

actually yeah now that i think about it the m1v1=m2v2 is right and made it clear for me thanks!

[slade]

My physics is a bit fuzzy (I had a moron for an AP Physics teacher who said things like "we don't call Fred 'Joe'. Thus, we do not call omega 'w'." But that's another story) but I would think that if the airplane isn't moving, then no lift can be generated. The conveyor belt is acting like friction, only friction... that acts in perfect opposition to the movement, rather than a fraction of it. I guess my point is that the engine can provide thrust, but the plane can only move forward as fast as the wheels are moving, and if the ground under the wheels is meant to move in perfect opposition, the plane will go nowhere.

But like I said, my physics are fuzzy.

at first i thought the guy was an idiot, because the way he words it it sounds like hes asking what would happen if the plane does not move, but the engines are running. of course it wouldnt take off, it needs to have air flowing past it.

the thing is, cars are powered through their wheels, they use contact with the ground to push themselves forward. thus a car on a conveyor belt would not move relative to the ground.

however, a plane is powered by a jet engine/propeller which both use the air. the wheels are only to support the plane while it is on the ground, they rotate freely. when the plane starts the engines pull it forward through the air. that is what powers the plane. the wheels just rotate to keep up with the plane as the engines power it forward. the belt would cause the wheels to rotate faster which would add friction and reduce the speed, but most likely a neglidgeable amount.

[tropical_fishy]

Miscue, the conveyor belt isn't keeping the plane from moving. It is simply moving in a reverse direction from the plane. The wheels are spinning freely, sort of like isolating the plane from a moving or stationary runway.

Except the problem says that no matter what, the conveyor belt's speed is exactly equal and opposite of the plane's.