Critical thinking exercise!

Ntypical · **Mon Oct 29, 2007 8:34 am Critical thinking exercise!**

This may make some peoples heads hurt.

Ok people. I am not sure of how many people have heard of this old physics question, but here goes.

This was originally a critical thinking exercise I learned in college, but I have seen it all over the internet on several dozen message boards over the years, so it seems a lot of other people have heard of it as well.

This is called Plane on a treadmill. Please think before you answer, and think hard.

A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

Will the plane be able to take off?

Please explain why you answered the way you did.

tomparis · **Mon Oct 29, 2007 10:12 pm**

No it will not.

It won't take off because no air is moving. If there is no air moving, there is no lift, therefore, the plane stays on the ground.

TrekkieMage · **Tue Oct 30, 2007 1:14 am**

Ntypical · **Tue Oct 30, 2007 7:02 am**

Ok I said think before you answer

. Why would there be no air moving over the wings? The plane can still move down the runway because the wheels are free spinning. Think of it like this.

----------------> Plane moving at 100 mph
----------------> Plane's wheels spinning at 200 mph
<-------------- treadmill spinning at 100 mph

So the relative speed of the plane to the ground around it is 100 mph. The planes relative speed in regards to the tread mill is 200 mph.

The treadmill can do nothing to stop the forward movement of the plane beause the plane does not achieve movement by power to the wheels like a car does.

Here is a short 5 minute video a Engineer friend of mine made. It should explain everything, as well as show you why it does take off.

Do not worry, ninety percent of the people asked this question instantly assume that the plane can not take off because they think of a plane like a car, so they think the plane can not move forward. It is a common misconception. I myself fell for the first time I was asked this question. But after reading it a dozen or so times I was able to ignore the red herring and move on to see that the plane can still move forward.

And if you really want to you can go here and read a 583 page discussion on the subject.

tomparis · **Tue Oct 30, 2007 1:26 pm Re: Critical thinking exercise!**

Ntypical · **Tue Oct 30, 2007 1:59 pm Re: Critical thinking exercise!**