Noticed while reading

[Michael Kieth Adams]

I’m just a retired science teacher who is interested in science. On the international space station, someone noticed that fine powders clumped in zero gravity.  First we must assume that they checked for electrical charges, if they did then if you can’t see what is causing an effect, maybe the cause is invisible as in dark matter or energy.  Just a thought.

[johninderby]

This article in Physics World might be of interest.

https://physicsworld.com/a/tiny-particles-dance-around-each-other-in-near-zero-gravity/

[saac]

Pretty sure there is an episode of Universe where Brian Cox shows how dust and fine particles are clumped together under electrostatic forces prior to gravity becoming the dominant role in their further aggregation of mass. He shows a nice demonstration using a perspex tank full of dust on a zero gravity flight. 

Jim 

Edited July 18, 2019 by saac

[Owmuchonomy]

Electrostatic forces dominate up to a radius of 1km, then gravity takes over. Above about 1000km radius the forces are sufficient to cause the formation of a sphere. That’s what I was taught and can be demonstrated via maths for substances of similar density to solar system debris. I still use the examples for outreach when chatting about my space rocks.

[saac]

Not the video I was thinking of but it conveys the same idea.

 

Jim 

 

[andrew s]

This agrigation is most likely due to surface electrostatic forces. Google "Particle aggregation in microgravity".

Regards Andrew 

[JamesF]

I thought it was less than 1000km radius to start to form a sphere, but perhaps I'm remembering miles.  I do recall Brian Cox doing a piece on it in one of his documentaries.  I just can't definitively recall the numbers.

James

[MarsG76]

Yes, I've seen a doco demonstrating this.. the start of a collapsing accretion disc...

 

[Owmuchonomy]

16 hours ago, JamesF said:

I thought it was less than 1000km radius to start to form a sphere, but perhaps I'm remembering miles.  I do recall Brian Cox doing a piece on it in one of his documentaries.  I just can't definitively recall the numbers.

James

Could be.  It's only an estimate based on a density of 6gm/cm3 from memory (which isn't what it was).