Easy Questions?

[Swatopluk]

That a normal planet could not take those forces is pretty obvious (neutron stars on the other hand can but they are both smaller and heavier). That question was a merely theoretical one (therefore the "rigid spherical body" part).

Answer is actually more easy than I thought. It is the speed of a circular orbit at the earth surface, i.e. about 7900 m/s.
For comparision: the actual speed at the equator is just 463 m/s, about a 17th of the necessary value.
I hadn't thought about the effect being limited to the equator when I put the question up, I admit, despite it being obvious.

[beagle]

Yep, mg= mvv/r

solved for v is the simplest way I can think of.

In a related area, would a gas-filled or evacuated tube of high diameter submerged in a high density incompressible fluid (i.e. lower pressure on the top, significantly higher on the bottom) still have the circle as ideal profile or would it go towards an ovaliform shape? In the latter case, would the "sharp" end be top or bottom?

My immediate reaction is that if the tube is lighter than the fluid  that it displaces then the shape will depend on the position of the mounting points holding it in place, with it arching upwards at the furthest positions from those points. I'd guess it would try to obtain a cross-section similar to that of a hot air balloon, but be constrained in its horizontal movement if held in place (depending on its supports).

Without constraints I'd expect a unifom hot-air balloon-oid cross-section, but that's a guess (don't fancy messing with the appropriate calculus of variations). Not sure how much of the HAB shape is due to non-uniform temperatures within it and the weight of the basket dangling precariously beneath it.

[Swatopluk]

I think the balloon of today is designed that way. Early ones also had more spherical forms on occasion. The first Montgolfieres looked more like lightbulbs with socket.
You are probably right about the mountings being the true stress points but let's assume the tube was heavy enough not to float.

[Griffin NoName]

The larger the beast, the longer it tends to live. How long did the largest dinosaur live for?

[Swatopluk]

Iirc the estimate is about 80-100 years but size is only one of the criteria determining that. Animals with slow metabolism tend to get older, those with very high die young (elephant turtles vs. jerboas). On the other hand the older an animal gets, the bigger it can become. Of course architeuthis has a very short lifetime (about 5 years iirc) but grows from tiny to huge. But squids are high metabolism creatures, so that would account for it.

[beagle]

Perhaps we should draw up longevity rules:

Taste bad.
Have a slow metabolism.
Don't provide any useful product.
Have a very nasty bite.
Have a nasty temper.
Live somewhere inaccessible.
Try and be adopted as sacred by the local tribe, or failing that GreenPeace.

[Sibling Chatty]

Doesn't work. I meet most of that list spot on, and my longevity is seriously in question...

[Griffin NoName]

I have Chasing Playback on my HD recorder which is a truly wonderful invention. But why is there no Chasing Playforward ? it'd be so useful when I have to go out before the programme is due to finish, especially in whodunits.... 

[Sibling Zono (anon1mat0)]

Wait, does Greenpeace adopts seniors? That sounds like a nice prospect...

[Swatopluk]

What makes dough so extremly sticky, while none of its components has that character?

[Darlica]

Usually it is the gluten protein, in combination with water.
(chemistry would be the really short answer)

As I understand it water makes it possible for the gluten protein chains to attach to each other building gluten strands.  Fat inhibits the formation of long gluten strands that's why a "crusty" dough like a pastry or shortbread dough often has a higher fat content.

http://en.wikipedia.org/wiki/Gluten

[Swatopluk]

And why are the gluten strands sticky?
Shouldn't it just behave like rubber? (that question should be quite tricky )

[Darlica]

I don't now, maybe Aggie can explain later he's the one with the Chemistry Fu.

To me chemistry is a equivalent to magic...
And I shouldn't really be trusted with a magic for kids kit nor a chemistry for kids kit...    

[Swatopluk]

I think the same about physics

[Sibling Zono (anon1mat0)]

Swato, you have been evil, why don't you answer the questions to which you already know the answer?