Rain & Energy

Alyeska · Post by **Alyeska** » 2006-08-06 01:19am

Now that is a calc I can sink my teeth into. Thank you.

Alyeska · Post by **Alyeska** » 2006-08-07 02:16pm

Cyborg Stan wrote:Hm. (Re)-plugging in in the GPE = m*g*h formula gives us

M = surface area of the Earth * depth of flood (assume a mere mile deep Flood) * density of water = 5.107*10^14 m^2 * 1609.344 m * 1000 kg/m^3
G = acceleration due to gravity = 9.8 m/s^2
H = height fallen = 50,000 m

divide this by 4.184*10^15 J per MT gives us around 97 billion megatons. If we just want MT per square km, we simply stick in 10^6 m^3 where the surface area of the Earth previously was, giving it around 188 MT per square km this time.

I tried repeating your calculations on my own, but I seem to be messing up somewhere.

Can you please recalc bassed on a height of 5km? An Ancient is getting picky about the fact that the raining is falling from a height of ~150,000 feet. So I figure he can be indulged with a height of 1/10 that.

Turin · Post by **Turin** » 2006-08-07 03:06pm

Alyeska wrote:Can you please recalc bassed on a height of 5km? An Ancient is getting picky about the fact that the raining is falling from a height of ~150,000 feet. So I figure he can be indulged with a height of 1/10 that.

Just divide by 10 in the earlier equation (because everything's being multiplied and you're changing from 50,000m to 5,000m). So 18.8MT per square kilometer or 9.7 billion megatons total.

Alyeska · Post by **Alyeska** » 2006-08-07 03:31pm

I figured it would be a simple case of multiplying by 1/10, but I wasn't sure.

This level of math and physics calculation is way beyond my education. Wish I had taken physics in college.

Post by **Darth Wong** » 2006-08-07 06:31pm

Alyeska wrote:I figured it would be a simple case of multiplying by 1/10, but I wasn't sure.

This level of math and physics calculation is way beyond my education. Wish I had taken physics in college.

I hate to break it to you but this is high-school level physics, not college-level. In a lot of these cases, it's not so much a matter of people not having taken college physics as it is a matter of people not having paid enough attention in HS. Either that or American high school covers a lot less than I think it does.

Alyeska · Post by **Alyeska** » 2006-08-07 07:12pm

I never took physics in high school either. Just chemistry and biology (didn't get very good grades either). I didn't really begin to appreciate science until I was mostly through college.

Turin · Post by **Turin** » 2006-08-07 08:05pm

Darth Wong wrote:I hate to break it to you but this is high-school level physics, not college-level. In a lot of these cases, it's not so much a matter of people not having taken college physics as it is a matter of people not having paid enough attention in HS. Either that or American high school covers a lot less than I think it does.

I hate to break it to you, but Physics was actually optional in my High School, and I went to high school in upstate New York, which has some of the best public high schools in the country. Pretty sad, isn't it?

Turin · Post by **Turin** » 2006-08-07 08:11pm

Turin wrote:I hate to break it to you, but Physics was actually optional in my High School, and I went to high school in upstate New York, which has some of the best public high schools in the country. Pretty sad, isn't it?

I just re-read that and I realized it came off as being snarky for no reason. Damn the lack of an edit feature! Sorry!

In any event, we had something called a Regents degree in New York, where you could take "extra" classes to acheive a high school diploma that was supposed to be above-and-beyond the norm. The additional classes included such absurdities as taking 4 years of math instead of 3, and taking 3 years of science classes instead of 2. I couldn't believe the number of students who didn't take the Regent's level classes (much less 4 full years of both math and science like I and the folks who wanted to move on to serious college programs took). American HS students just don't see the importance of math and science, and it's a combination of their own bad attitudes, their parent's idiocy, and the idiocy of the administrations who allow it.

Cyborg Stan · Post by **Cyborg Stan** » 2006-08-07 10:16pm

Alyeska wrote:I tried repeating your calculations on my own, but I seem to be messing up somewhere.

Can you please recalc bassed on a height of 5km? An Ancient is getting picky about the fact that the raining is falling from a height of ~150,000 feet. So I figure he can be indulged with a height of 1/10 that.

I'm making my own response, but the 50 km figure is NOT really the height most of water is falling - it is merely an average. (Since we're using the simple formula, this is okay.) Remember, clouds != coherent blob of water.

As for the formula, it's just a simple case of Work = Force * Distance.

Post by **Beowulf** » 2006-08-07 10:54pm

In my high school, you were required to take two science classes. Physics wasn't required, (I ended up taking 4 science classes, but I was wierd like that).

Alyeska · Post by **Alyeska** » 2006-08-08 12:43am

Cyborg Stan wrote:
Alyeska wrote:I tried repeating your calculations on my own, but I seem to be messing up somewhere.

Can you please recalc bassed on a height of 5km? An Ancient is getting picky about the fact that the raining is falling from a height of ~150,000 feet. So I figure he can be indulged with a height of 1/10 that.
I'm making my own response, but the 50 km figure is NOT really the height most of water is falling - it is merely an average. (Since we're using the simple formula, this is okay.) Remember, clouds != coherent blob of water.

As for the formula, it's just a simple case of Work = Force * Distance.

You have my thanks. An Ancient knows just enough science to make things difficult for me since he can throw up a nice smoke screen.

Turin · Post by **Turin** » 2006-08-08 10:23am

Okay, now it's my turn to feel dumb. Just for kicks, I wanted to run the numbers myself using my own assumptions (like the "15 cubits" number in Genesis 7:19-20, which would put the flood depth at 8857m... I then assumed a very low-ball height of 9000m for the fall). I ended up with 3.99e26 J for the total energy from GPE, which jives pretty well with the 95 billion megaton figure.

But then I wanted to try to figure out the effects of dumping this much energy into the atmosphere... which is a simplification as some would end up heating the water and some the atmosphere, and some the crust if the waters all boil off. I thought I could use the specific heat formula, but I'm getting a number that seems way off.

specific heat of air: 1.012e3 J / kg / K
total mass of Earth's atmosphere: 5.3e18 kg

Q=m*c*dT
dT = Q/m*c
dT = 3.99e26 J / (5.148e18 kg * 1.012e3 J/kg/K) = 7.66e4 K

I'm getting the feeling I might just be using the wrong formula or making some wrong assumptions here. Anyone better educated than I care to give a point in the right direction?[/url]

Raven · Post by **Raven** » 2006-08-10 05:08pm

Turin wrote:Okay, now it's my turn to feel dumb. Just for kicks, I wanted to run the numbers myself using my own assumptions (like the "15 cubits" number in Genesis 7:19-20, which would put the flood depth at 8857m... I then assumed a very low-ball height of 9000m for the fall). I ended up with 3.99e26 J for the total energy from GPE, which jives pretty well with the 95 billion megaton figure.

But then I wanted to try to figure out the effects of dumping this much energy into the atmosphere... which is a simplification as some would end up heating the water and some the atmosphere, and some the crust if the waters all boil off. I thought I could use the specific heat formula, but I'm getting a number that seems way off.

specific heat of air: 1.012e3 J / kg / K
total mass of Earth's atmosphere: 5.3e18 kg

Q=m*c*dT
dT = Q/m*c
dT = 3.99e26 J / (5.148e18 kg * 1.012e3 J/kg/K) = 7.66e4 K

I'm getting the feeling I might just be using the wrong formula or making some wrong assumptions here. Anyone better educated than I care to give a point in the right direction?[/url]

The math is fine, but consider that you'd end up heating the water too, and not just the atmosphere. 4.5e21 kg water at the atmosphere would gain about 20 degrees C or so.

Notice how piddly the atmosphere is compared to the water; I like how Ancient claims the atmosphere would act as a good heat sink, and won't admit the only way the energy can leave the Earth is by radiating into space.

Turin · Post by **Turin** » 2006-08-10 06:13pm

Raven wrote:The math is fine, but consider that you'd end up heating the water too, and not just the atmosphere. 4.5e21 kg water at the atmosphere would gain about 20 degrees C or so.

I thought of that... but all but a tiny fraction of the energy from a rain drop would go into the atmosphere, at least according to this link posted by GrandMasterTerwyn in one of the earlier threads.

Wyrm · Post by **Wyrm** » 2006-08-10 06:54pm

Turin wrote:Q=m*c*dT
dT = Q/m*c
dT = 3.99e26 J / (5.148e18 kg * 1.012e3 J/kg/K) = 7.66e4 K

I'm getting the feeling I might just be using the wrong formula or making some wrong assumptions here. Anyone better educated than I care to give a point in the right direction?[/url]

The specific heat of air is not a constant with temperature, humdity or air pressure (elevation), so your answer is a little wrong, but probably within an order of magnitude or so of the right answer. Only at very small changes in temperature does specific heat approach a constant. (Notice that the Wikipedia article has two values for air.)

Another thing is that, yes, the atmosphere is going be getting damn hot in the global flood scenario. ~4e26 J is a fuckload of energy, even by planetary standards. The sun produces on order of this energy every second, total (we only catch a small fraction of this). I'm wondering what temperature you were expecting.

Turin · Post by **Turin** » 2006-08-10 07:09pm

Yeah, the specific heat number I used was a simplication because I would have a heck of a time modelling the increase in specific heat as the pressure and humidity went up. I suppose you could calculate the highest pressure and humidity possible with the extra mass of water in the atmosphere and use that as a lower-limit of temperature, but like you said "within an order of magnitude" is good enough for me for now.

Wyrm wrote:Another thing is that, yes, the atmosphere is going be getting damn hot in the global flood scenario. ~4e26 J is a fuckload of energy, even by planetary standards. The sun produces on order of this energy every second, total (we only catch a small fraction of this). I'm wondering what temperature you were expecting.

Crickey! I just looked up the sun's luminosity for myself and you're right! Instinctively I was thinking hot oven-like temperatures (300-400C or something, certainly not remotely survivable by life)... shows me what I get for not trusting the math.