It's Friday..

[Tunicates]

Originally Posted by David G

Here is a totally pointless banal debate for you:

Imagine a plane is sitting on a massive hypothetical conveyor belt, as wide and as long as a runway. The conveyor belt is designed to match the speed of the plane exactly but moves in the opposite direction. The engines are running at take-off thrust, the brakes are off, etc. Everything is normal save for the fact the plane is on a treadmill.

Can the plane take off?

David.

OK, the torus faeces has been exposed as bullshit, and this plane can now fly - cos its pushing air, and nothing to do with what the ground is doing right?

Now I have a question.
Assuming that this plane takes off at 150 mph......
What speed is the rubber at the top of the wheels doing?

Green for the right answer.....

[Lazlo]

Originally Posted by Tunicates are Mad

OK, the torus faeces has been exposed as bullshit, and this plane can now fly - cos its pushing air, and nothing to do with what the ground is doing right?

Now I have a question.
Assuming that this plane takes off at 150 mph......
What speed is the rubber at the top of the wheels doing?

Green for the right answer.....

Um ... 300 mph ?

[Adrian Kelland]

Originally Posted by Tunicates are Mad

OK, the torus faeces has been exposed as bullshit, and this plane can now fly - cos its pushing air, and nothing to do with what the ground is doing right?

Now I have a question.
Assuming that this plane takes off at 150 mph......
What speed is the rubber at the top of the wheels doing?

Green for the right answer.....

Depends on the diameter doesn't it? Or is this a trick question?

[Lazlo]

I started doing it from first principles:

Velocity at tangent of a circle rotating in place = 2 π r

which would make the top of the wheel moving forwards at 2 π r and the bottom of the wheel moving backwards at 2 π r.

Then if you move the whole thing forwards by a velocity equal to 2 π r (a) then the top is going at 4 π r and the bottom is now stationary - which is the situation here.

However, that velocity (a) must equal 150 mph! So the answer is 4 π r = 300 mph.

The tangential velocity is directly proportional to the radius given the same period, or to put it another way, if you halved the period and doubled the radius, you'd get the same tangential velocity.

I think ...

[Tunicates]

Originally Posted by Lazlo

I started doing it from first principles:

Velocity at tangent of a circle rotating in place = 2 π r

which would make the top of the wheel moving forwards at 2 π r and the bottom of the wheel moving backwards at 2 π r.

Then if you move the whole thing forwards by a velocity equal to 2 π r (a) then the top is going at 4 π r and the bottom is now stationary - which is the situation here.

However, that velocity (a) must equal 150 mph! So the answer is 4 π r = 300 mph.

The tangential velocity is directly proportional to the radius given the same period, or to put it another way, if you halved the period and doubled the radius, you'd get the same tangential velocity.

I think ...

Have you taken the speed of the conveyor belt into consideration?

[Tunicates]

Originally Posted by Adrian Kelland

Depends on the diameter doesn't it? Or is this a trick question?

Trick only in that there is a pratfall. An answer in mph would depend on the diameter, so I'll accept theoretical answers.

[Woz]

It's the same as the speed at the bottom of the wheel which is the same as the speed of the ground that it is touching. You might want to add a conveyor belt too it too if you are sad and lonely and have never touched another human.

[Lazlo]

Originally Posted by Tunicates are Mad

Have you taken the speed of the conveyor belt into consideration?

Conveyer belt?

Oh well then, in that case ...

Originally Posted by Woz

It's the same as the speed at the bottom of the wheel which is the same as the speed of the ground that it is touching.

... wot he said. Assuming that the wheel is stationary (but turning).

[Tunicates]

GGgggrrrrrrrrr You guys!

The plane, was already on a bloody conveyor belt remember? I didnt put it there! Going at the same speed as the plane, but in the other direction.......
It was supposed to trip you up.
Actually, it tripped me up. It doesnt depend on the diameter of the wheel.
It only depends on the speed of the aircraft and the speed of the ground

The bottom of the wheel in this instance is going 150 mph but in the opposite direction to the plane.

The plane is doing 150mph.
The top of the wheel is spinning twice as fast as the difference between the axle and the ground - in this case the diffference is 300mph - so the rubber at the top is doing 600mph.

The top of the wheel is going the same speed as the aircraft, ie 150mph, but the rubber at the top of the wheel is going a lot faster, because of the stupid conveyor belt.

Isnt it?

[Scu-bamboo]

On the bus to college, we always seem to have really serious talks about what we would do if we had Bernard's watch! What would you do if you had Bernard's watch?