Solving the Physics Problem of 20 Tons in a 10 Ton Van

[Hypercase]

While driving down the road one day, a motorist sees a truck (closed van) coming up behind him rapidly. The van passes him, but a short time later he sees it parked along the road, and the driver is out beating the side of the truck with a tire iron. He goes on, and soon he sees the truck rapidly approaching again. This scenario repeats several times. His curiosity perked, the next time he sees the truck stopped, he stops also, and queries the driver.

"Well, I have 20 tons of canaries in here, and this is a 10 ton van, so I am trying to keep them flying"!

What is wrong with the physics??
If the van was a cage instead of closed wat diffrence would it make?

 

[Chen]

Heh, I was just reading about this the other day while looking for familiar physics myths and common misconceptions. :)

Look here:
http://www.lhup.edu/~dsimanek/scenario/miscon.htm
Under "Fly away, birdie."

 

[Hypercase]

That still doesn't answer the question.

 

[AKG]

Hypercase

If the canaries are to stay in the air, an upwards force has to be exerted on them, which is normally done by the air which their wings beat down on. But the air in the van stays where it is, it doesn't go accelerating through the bottom of the van. It will have to apply a force on the van, probably on the bottom of the van, I would think, and this would be equivalent to the weight of the canaries if they were all still. If they were in a cage, I have a feeling it would be slightly different. In fact, even in the case of the van, it may be different than what I described. However, at this point you're talking about the turbulent motion of air and I have a feeling that the force of the air won't go straight down to the bottom of the van, it will swirl around, but I don't know enough about this to say how it will behave. One thing is, however, that birds wings are designed to let them glide on currents of wind, so maybe an open cage on a moving vehicle would be different because the canaries might be able to just glide through the air, and they'd stay in the air because of the difference in pressure above and below their wings, but at this point I have no idea what I'm talking about...

 

[Hypercase]

ok now that the idiots have had their chance can some who knows wat their talking 'bout answer my question please...

 

[chroot]

Hypercase,

Your question has been quite well answered. AKG is no idiot. I should also add that personal attacks are not welcome here at PF.

- Warren