Science questions not worth a thread I: I'm a moron!

[nc-1701]

Surface area of a sphere is 4*Pi*r^2, radius of the moon is 1737.1 km. So the surface area is about 37900006.1096 km^2.

Surfacearea of Earth with radius of 6371 km would have an area of 509805890.96 km^2.

Divide them and we get that the moon would cover about 7.4% of the Earth's area.


Math ftw

 

[Cutlass]

Well given it's total surface area...

You didn't say surface area. The volume of it is much greater.

 

[Bluemofia]

You didn't say surface area. The volume of it is much greater.

Also similar to the "what is the length of the coastline of Britain" problem.

Depends on your precision of measurement.

 

[Perfection]

Surface area of a sphere is 4*Pi*r^2, radius of the moon is 1737.1 km. So the surface area is about 37900006.1096 km^2.

Surfacearea of Earth with radius of 6371 km would have an area of 509805890.96 km^2.

Divide them and we get that the moon would cover about 7.4% of the Earth's area.


Math ftw

Why the hell not just look up the surface area stats instead of approximating them?

Math FTL.


Also, if for some reasons it was easier to look up radius, then you'd just calculate

rmoon^2/rearth^2

smart math FTW

 

[Xanikk999]

What is the finest substance known (Either man made or natural)?

 

[uppi]

What is the finest substance known (Either man made or natural)?

What do you mean with "finest"? The purest?

 

[madviking]

I think he means by grain.

 

[ParadigmShifter]

It's made easier by the fact it is 4x the damage of a single D4* (let's call it D4*).

I think the average damage for a D4* will be

2.5 + 0.25 * 2.5 + 0.25^2 * 2.5 ...

= sum( n = 0 to inf ) 2.5 * 0.25^n

= 3 1/3

(from Wolfram Alpha http://www.wolframalpha.com/input/?i=sum(+n+=+0+to+inf+)+2.5+*+0.25^n )

so it would be 3.333.. * 4 = 13.333...

 

[ParadigmShifter]

Yes, it's a geometric series

EDIT: Proof here: http://en.wikipedia.org/wiki/Geometric_series

 

[ParadigmShifter]

Is there a closed form for that?

Thanks, that's my intuitive answer, but being math-stupid I didn't even know you could do infinite summations (and even if I did, I'd still be looking for a closed form...)!

Sometimes you can do infinite summations. It's often hard to find a closed form solution, for example

1 - 1/3 + 1/5 - 1/7 + 1/9 - ... = pi/4

which needs trigonometry and integration to prove.

 

[ParadigmShifter]

OH. Wow. a/(1-r), seriously? Thanks!

The series only converges to a/(1-r) if r < 1.

EDIT: Actually, if |r| < 1 i.e.

-1 < r < 1

EDIT2: Fascinating subject convergent series anyway.

 

[sanabas]

EDIT2: Fascinating subject convergent series anyway.

Yep. Also, occasionally having a brain like a sieve can be fun. Last time I tried to remember the formula for sum of a geometric progression, I couldn't, so got to sit down & derive it & prove it myself. Was fun.

 

[tycoonist]

Yep. Also, occasionally having a brain like a sieve can be fun. Last time I tried to remember the formula for sum of a geometric progression, I couldn't, so got to sit down & derive it & prove it myself. Was fun.

I like to prove the mathematical formulas i used in the half hour i always have left in my maths exams

 

[Xanikk999]

What is the finest substance known (Either man made or natural)?

I think he means by grain.

Yes this is what I mean anyone know?

 

[Eran of Arcadia]

I once read that solid hydrogen would be a monatomic powder but don't know if that is true (or possible).

 

[IdiotsOpposite]

What is the geometric significance of a line integral over a vector field?

 

[SS-18 ICBM]

I once read that solid hydrogen would be a monatomic powder but don't know if that is true (or possible).

Don't think there would be too many intermolecular forces at work, so it might be the case. I don't know about possible quantum effects though.

 

[uppi]

I once read that solid hydrogen would be a monatomic powder but don't know if that is true (or possible).

Don't think there would be too many intermolecular forces at work, so it might be the case. I don't know about possible quantum effects though.

No, Hydrogen usually builds a H₂ molecule, so a crystal built from Hydrogen is usually diatomic. Helium is the atom that is hardest to get to bound with other atoms.

The original question is hard to answer without some boundary conditions. The answer very much depends on how exactly you define grain and what states of matter you allow.

One can make the case, that there are states of matter, that have atoms, protons, electrons or even photons as the particles that make up grain. So one could argue, that the smallest grain is exactly zero (and it gets quite muddy here, as we do not know whether some particles have a "size" larger than zero).

But thinking of photons as grains is quite strange and probably not the intention, so a stringent definition of grain is needed (and keep in mind, that one can make pretty exotic states of matter that defy the common classifications). If you have such a definition, pick the smallest particle that fits it and you have the answer.

 

[tycoonist]

I once read that solid hydrogen would be a monatomic powder but don't know if that is true (or possible).

I can't see why it would be monatomic, looking at the question from a chemistry point of view. I guess there could be quantum effects on that scale.

 

[Narz]

Another question about the aging process.

If aging is mostly caused by improper cell division &/or mutations (probably a gross oversimplification, feel free to amend/correct) then how does anti-aging occur? Do the cells actually repair themselves?

I ask because I don't want to get old! I'm having a lot of issues with stress & undersleeping & I know I'm causing my body some damage & want to make up for it.