Stupid Science Questions 2

14:49 / 01.07.08

if all you need for a balloon to rise is heated air, and all you need to do to heat air is a kind of greenhouse effect...

wouldn't a transparent/translucent balloon kind of just rise on its own on a sunny day? maybe you need to paint the bottom black?

15:05 / 01.07.08

I believe, but have no proof, that the lift from the heated air is too small to overcome the gravitational forces pulling the mass of the balloon back towards ground. So, if the ratio of temperature x volume / mass* is great enough, we all know that hot air balloons will rise. There's some ratio threshold above which the balloon will rise. However, I doubt if you'd get enough thermal energy from the sun alone, at least outside a very hot climate.

* Not sure this is the correct formula.

Evil Scientist

15:06 / 01.07.08

I didn't think you could.

However...

Solar balloons say yes! Kind of anyway, the material would have to be black rather than transparent to capture the heat.

According to this website you can make one out of bin bags.

Happy flying!

15:39 / 01.07.08

Coo-al! I know I'd never go up in one though.

15:54 / 01.07.08

thanks for the info!

I really need to get some kind of workshop set up so I can experiment with weird little projects like this. though I suppose NYC doesn't approve much of private flying projects.

some of their pictures showed models with a clear panel or two - I think one balloon was totally clear. I'd be interested in playing with different mixes and seeing for myself how the lift and inner temp change.

also wondering how you could work solar panels in there somewhere and how it would change the heat.

grant

17:54 / 01.07.08

What do you mean by "solar panel"?

18:03 / 01.07.08

photovoltaic cells?

something to power the electric motor on my imaginary solar zeppelin?

grant

15:55 / 02.07.08

You might be better off with something like this:

the Magenn balloon turbine.

Although... hmm.

The problem with a balloon is that the part that's getting hot is opaque and I imagine moves around relative to the sun, so no good for photovoltaics. You'd need to put them on a boom, I think, with some kind of allowance for the way the balloon blocks the sun at certain angles.

The turbines seem like a natural, except balloons move *with* the wind, and the turbines need to have wind move *against* them. Relative windspeed and all that.

grant

15:59 / 02.07.08

Although a *dirigible* has a firm body, so photovoltaics could be mounted outside it, like this one (also on YouTube). But it uses helium to fly, not hot air.

16:05 / 02.07.08

it might be completely unworkable, just one more idea rolling around in my head when I think about balloons and zeppelins and stuff.

I'm still thinking, top hemisphere of balloon is transparent to allow more sunlight to get inside, bottom hemisphere of balloon is black so it heats up and gets trapped. solar panels would be on that black surface, inside the balloon.

solar panels do get hot, it seems (45 C), because they're inefficient and only absorb sunlight within a certain bandwidth and waste the rest. but I assume they don't get as hot as flat black fabric would since they are using some of the light, so your balloon wouldn't get as much hot air. and extra weight too. maybe a dumb idea.

in the end the whole thing stops working if the sun goes down. big limiting factor there.

All Acting Regiment

12:25 / 11.07.08

'Every action has an equal and opposite reaction'. Is this still true?

Quantum

12:29 / 11.07.08

Yes.

Evil Scientist

12:46 / 11.07.08

I suppose so, in that the exact opposite of something happening is something not happening.

Evil Scientist

12:46 / 11.07.08

Bloody hell! Quantum sighting!

Proinsias

21:41 / 03.11.08

If the universe is around 14 billions years old, is around 93 billion light years in diameter and stuff doesn't travel faster than the speed of light then how does that work?

I recall reading an explanation sometime ago and filing it away in brain but it seems the filing system is not what I thought it was.

jentacular dreams

21:46 / 03.11.08

I suspect it's because of the space between things expanding, especially in the early moments of the 'verse, but I'm a biologist so don't take my word for it.

Proinsias

21:55 / 03.11.08

I think you're correct. I'm now thinking it was in Impossibility by James D Barrow that I read it but I'll be damned if I can find it.

05:06 / 04.11.08

Cosmic inflation, or to be even more pedantic, the metric expansion of space. Basically the idea above, that the relative separation of parts in the universe increases.

Wiki

Proinsias

23:06 / 04.11.08

Perfect.

16:48 / 18.11.09

Is it theoretically possible for a plant to get its energy from IR Radiation rather than UV radiation? IF so how would that effect how it looked (colour, leaves etc.)?

17:01 / 18.11.09

Don't know about plants, but certain anaerobic bacteria power their photosynthetic activities using IR radiation. This happens for example around deep-sea hydro-thermal vents, where the IR/blackbody radiation from the vents is used by bacteria as a power source.

09:51 / 19.11.09

That's a good point because there is other life not relying on the sun for energy down amongst the vents I believe.

Thanks you very much.

15:13 / 16.02.10

Does anyone know where I can find what the distance would be between asteroids in a family in the Asteroid belt?

Quantum

21:02 / 16.02.10

Mostly hundreds of thousands of km apart here's a list of the prominent families and a quote-
The asteroid belt is usually thought of as a defined region where asteroids abound (reference many science fiction movies, with spaceships flying in and out, dodging debris). This is actually very unlike the asteroid belt -- the region is so vast that asteroids are usually hundreds of thousands of kilometers from their closest neighbor. If the asteroid belt were taken to be the width of its densest region (3.2-1.8 A.U.), and it were considered flat, it would have an area of about 6·1017 km2. Even if there are 1000 times more asteroids than we know of today, then on average each asteroid would have over one million km2 to itself.
http://burro.astr.cwru.edu/stu/advanced/asteroid.html