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Sunday, February 23, 2020

If there was a tank that could hold 10000 tons of water and had a finger - width hole at the bottom and you put your finger on/in the hole, would the water not drain or push your finger out?

If there was a tank that could hold 10000 tons of water and had a finger - width hole at the bottom and you put your finger on/in the hole, would the water not drain or push your finger out?


If there was a tank that could hold 10000 tons of water and had a finger - width hole at the bottom and you put your finger on/in the hole, would the water not drain or push your finger out?

Posted: 22 Feb 2020 12:52 PM PST

How much blood can a human body receive from a donor in one go. Can excessive blood cause the veins and arteries to burst due to the buildup of pressure?

Posted: 22 Feb 2020 08:12 PM PST

For example, a balloon can pop if it's over inflated, can this happen inside the veins and arteries?

submitted by /u/khizee_and1
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Is Ohm's law still valid if the Electric field isn't uniform through a conductor? Is it possible to prove that vector and scalar form of Ohm's law are equivalent with this condition? How?

Posted: 23 Feb 2020 07:03 AM PST

As this website and other textbooks shows, to pass from the microscopic to macroscopic version of Ohm's law, these assumptions are made:

• E=∆V/L which is only true if the field through the conductor is uniform.

• J=I/A that due to its definition implies that the direction of the drift speed of electrons is the same as the normal vector of the conductor's surface.

But this can't be true considering we are assuming pJ=E and E, since the conductor isn't in electrostatic equilibrium anymore, is the field inside of the conductor generated by the current. So it makes sense for me that E can be considered uniform because is almost always tangencial to the path, but then again, the direction of J and E can't be the same to make these 2 assumption simultaneously, am I right? What am I missing in this analysis?

Also, I couldn't find anything mathematically rigorous on this particular issue, like how is it possible that we can have a vector and scalar form of Ohm's law that are equivalent? Is the law actually the module of J and E or why is the vector form which is correct?

submitted by /u/ValGriff
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How long can viruses survive on a p95 mask or filter?

Posted: 22 Feb 2020 10:53 PM PST

Why is the size of noble gases larger than the previous halogen?

Posted: 23 Feb 2020 01:46 AM PST

How do our bodies produce electricity with electrolytes? What are these electrolyte cells made out of? When the iron gates of these electrolytes open, to flip the charge inside and outside the cell, how does it make sure the wrong charge doesn't go to the wrong place?

Posted: 22 Feb 2020 07:07 PM PST

The question is all in the title. I've googled these things extensively and i can't find anything. I am grade 9 for context, just in case these questions are retarded.

submitted by /u/Echszerox
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Why are the craters on the moon so shallow and flat?

Posted: 22 Feb 2020 08:56 PM PST

From pictures I have seen online, many of the craters on the moon are perfectly circular, 10s of km in diameter but very shallow and perfectly flat.

Shouldn't craters caused by asteroid impacts be deeper? The moon also has no atmosphere/water, so no erosion. Without erosion how could the craters be so flat?

submitted by /u/anoobis95
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If I point a laser at the moon and quickly flick my wrist, will the red dot of light on the moon move faster than the speed of light?

Posted: 22 Feb 2020 04:17 PM PST

Can viruses evolve to become resistant to vaccines?

Posted: 22 Feb 2020 06:42 PM PST

With the anti-vaccination movement getting larger and larger by the day, if there comes a day where they overwhelm crowds of vaccinated people, is it possible over time for viruses to evolve to become resistant to vaccinations? I know bacteria have mutant genes that allow them to be resistant to antibiotics, and i'm wondering if that may be something that we'll begin to see in viruses.

submitted by /u/djm0360
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Were there ever more than 9 planets?

Posted: 22 Feb 2020 09:22 PM PST

Years ago, I recall reading that there were once more celestial bodies classified as planets (12, I think). I believe they were some of the first asteroids discovered in the asteroid belt and were later declassified as planets after more and more of them were found. Much like how Pluto was declassified after more and more celestial bodies were found in the Kuiper Belt, correct? I can't seem to find any info about this. I wanna say this was in the 1920s or 30s.

submitted by /u/MHendy730
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Why is absorption spectra of a molecule bell curved?

Posted: 22 Feb 2020 11:29 PM PST

For a molecule, with a particular lamba max; at that wavelength the absorbance is read to be highest in the spectrophotometer. But I'm interested to know why does the absorbance decrease as we decrease the wavelength( or increase the energy), as the energy gap between HOMO and LUMO can be easily crossed at higher energies.

submitted by /u/arijeet_el_beatle
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Why is potassium needed to create an action potential in nerve cells?

Posted: 22 Feb 2020 03:46 PM PST

In nerve cells, sodium is actively pumped outside of the axon, while potassium is pumped to the inside. Because more sodium is moved outside than potassium is moved inside, the outside of the axon becomes positively charged relative to the inside, and an action potential is created. This allows the nerve cell to send an impuls along the axon by opening sodium channels and removing the action potential.

My question is: why is potassium needed in this situation? You're trying to get an action potential, so pumping positively charged ions to one side of a membrane makes sense. However, sodium and potassium are both positively charges ions, and you're pumping them in opposite directions. Wouldn't it be easier to pump sodium to one side of the membrane, and a negatively charged ion to the other? Or even to only pump sodium to one side of the membrane, and not use potassium at all?

submitted by /u/Byak0
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Why are angular momentum and each of the linear momentums (in the x,y, and z directions) all conserved independently?

Posted: 22 Feb 2020 09:59 PM PST

How do quantum computers use amplitudes to find a definite solution?

Posted: 22 Feb 2020 09:24 PM PST

Apologies in advance if this is a stupid question, I'm not the brightest. I recently listened to Scott Aaronson's conversation with Lex Fridman, and an interview he did for Scientific American, regarding quantum computing (QC from now on) and have a question regarding how a QC finds a solution.

This is an excerpt from the interview:

"In particular, if an event can happen one way with a positive amplitude, and another way with a negative amplitude, those two amplitudes can "interfere destructively" and cancel each other out, so that the event never happens at all. The goal, in quantum computing, is always to choreograph things so that for each wrong answer, some of the paths leading there have positive amplitudes and others have negative amplitudes, so they cancel each other out, while the paths leading to the right answer reinforce."¹

My question(s) is the following:

I) When he talks about choreographing amplitudes, is he essentially saying that we take a problem with a vast solution space, of which we know a large subset of true and false solutions, and try to "collapse" the correct wave function by cancelling out what we assume to be false values and reinforcing amplitudes that converge toward the correct answer; then hope the final measurement "collapsed" the correct solutions' wave function?

II) If that is the case, do we square the amplitude of that solution, as we do in physics, to get a probability? If so, does that mean we only get a value for the probability of that particular solution being the right one?

III) If we have to know so much about the solution in the first place and the challenge is programming an algorithm to get the correct solution, would it be impossible to have novel solutions to problems in which we have no epistemological priors about the possible solution space?

Apologies again if this is a silly question and thank you in advance for taking the time to answer it.

[1]

submitted by /u/dunnolol123
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How to Salmon survive in both freshwater and saltwater?

Posted: 22 Feb 2020 01:38 PM PST

What is quintessence?

Posted: 22 Feb 2020 06:44 PM PST

I was reading about dark energy and I heard of quintessence. I looked it up and most results I got weren't very helpful since they talked about a lot of complicated physics. So I came to ask, what is quintessence and what does it have to do with dark energy?

submitted by /u/MetaPyro
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Since our stomach acid is a strong acid, when we drink water does it react with that acid and form H3O+ in our stomachs?

Posted: 22 Feb 2020 12:18 PM PST

Why does your skin secrete electrolytes when sweating?

Posted: 22 Feb 2020 09:48 AM PST

If Betelgeuse is dimming and is 650 light years from earth is it possible it's already went supernova?

Posted: 22 Feb 2020 01:28 PM PST

How do genes build bodies?

Posted: 22 Feb 2020 08:01 AM PST

I understand that during the embryo stage, certain genes are turned on and off to control the building of a body plan. What I don't understand is how these genres "know" when to be turned on when to be turned off?

submitted by /u/viceni
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Is mRNA stored in our cells? Do we have a reserve if lets say RNA polymerase II stops working?

Posted: 22 Feb 2020 11:24 AM PST

Does the degree of polyploidy in plants have anything to do with the intensity of solar radiation they receive?

Posted: 22 Feb 2020 10:50 AM PST

Saturday, February 22, 2020

What is the difference between a cell which is alive and one which is not?

What is the difference between a cell which is alive and one which is not?


What is the difference between a cell which is alive and one which is not?

Posted: 21 Feb 2020 02:40 PM PST

How do supersonic planes operate?

Posted: 21 Feb 2020 07:25 PM PST

Wondering how supersonic planes actually work? I couldn't find anything on the google so I was questioning if you worthy redditers could enlighten me.

submitted by /u/guyoto
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What's the difference between the metrics in differential geometry and general relativity?

Posted: 21 Feb 2020 05:07 PM PST

This past semester I took a general relativity class and a differential geometry class.

In general relativity, we talked very early on about the metric tensor of a system of coordinates, like spherical or cylindrical coordinates, as basically a 3x3 diagonal matrix g=[g1; g2; g3] used to calculate length.

On the other hand, in differential geometry, after talking about parametric surfaces, the metric was defined to be a 2x2 matrix g=(E; F; F; G), with E, F, G being the first fundamental form of the surface.

Now, obviously, the two matrices cannot be equal, one being 2x2 and the other being 3x3. So I thought maybe they just have some of their elements to be equal. Which happens to be true but could be just coincidence. The metric of a sphere and the metric of spherical coordinates seem to be two completely different things, yet they share the same name and seem to have similar functions.

I even emailed my professors, the GR one had no idea what I was talking about, the DG one just told me I should read up on do Carmo's book on Riemannian geometry, which I was able to find, but was a bit over my head and couldn't find what I was looking for. I tried googling the question but I couldn't find anything related, so I don't think I was phrasing the question correctly. So what is the difference between the metric of a parametric surface and that of a system of coordinates? Is there some connection between them?

submitted by /u/harry353
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Is a metric and a metric tensor the same thing?

Posted: 21 Feb 2020 05:09 AM PST

Hi all, I am new to differential geometry, but I am reading about metrics and metric tensors now. My understanding is that metric tensors tell you how to find the length between 2 infinitesimally close points, while a metric provides a distance measure between any 2 points. My question is: are the 2 concepts equivalent or otherwise connected? If you have a metric, i.e. a distance measure, can you always find a metric tensor? What about vice versa? Save me!

submitted by /u/bobbytan85
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How did the Space Shuttle "balance" itself when the SRB's were dropped?

Posted: 21 Feb 2020 12:14 PM PST

I was watching a video of the last Space Shuttle launch and after a while, the two solid rocket boosters were dropped, and the SS was flying with only the big main tank attached. Since the three engines were so off-centre from the centre of mass (I presume), how did the whole thing not spin out of control?

submitted by /u/ruup20
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Questions about High and Low Explosives?

Posted: 20 Feb 2020 11:40 PM PST

First, I am not trying to make an explosive device, I am purely curious as to the chemistry and how they explode.

I understand that gunpowder is a low explosive, so it would need to be pressurized to make an explosion, so thats why it is good as a propellent for bullets.

But I have some questions...

  1. Do high explosives, such as tnt or picric acid have to be contained or pressurized for them to explode or do they explode if they are just on a plate since the pressure and the explosion is so fast?
  2. Could the military add a high explosive to a low explosive (gunpowder), and make the gun powder a high explosive?
  3. How come you need a certain amount of a high explosive to explode a low or another high explosive? (This is super confusing because I would think if you took a high explosive like tnt and tried to set off another high explosive like anfo ig, but videos show it not working.)
  4. Lastly, if the military were making warheads or missiles, would they use a high explosive to start the explosion, would the missile have a high, super sensitive explosive to then explode a low explosive? Or would this not work?
submitted by /u/Nick_9903
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How does a PC obtain an IP address?

Posted: 20 Feb 2020 11:36 PM PST

I am pretty new when it comes to IT, but I am trying.

The question is - According to what data does DHCP assign an IP address to your PC? Is it according to some components inside?

And if so, when I upgrade my PC over time, how does my IPv4 stay the same when there are not the same components inside?

submitted by /u/yolopes_nocz
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How do you differentiate essential fatty acid from non-essential fatty acid?

Posted: 20 Feb 2020 10:26 PM PST

Since both of them can either have a saturated carbon, or unsaturated carbon, I couldn't quite grasp how they differ.

How can one distinguish it from the other?

Edit: i forgot to mention, how do they differ "structurally"?

submitted by /u/Zephynx4476
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Why are there prominent HZE ions in cosmic rays, instead of a high variation?

Posted: 20 Feb 2020 09:18 PM PST

I am doing some reading and came across ultra-high energy cosmic rays, including HZE ions. According to Wikipedia (great source, I know) carbon, oxygen, magnesium, silicon, and iron are prominent HZE ions. But why those specific nuclei, that seem almost random?

submitted by /u/Eluisys
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Friday, February 21, 2020

If 2 photons are traveling in parallel through space unhindered, will inflation eventually split them up?

If 2 photons are traveling in parallel through space unhindered, will inflation eventually split them up?


If 2 photons are traveling in parallel through space unhindered, will inflation eventually split them up?

Posted: 21 Feb 2020 05:02 AM PST

this could cause a magnification of the distant objects, for "short" a while; then the photons would be traveling perpendicular to each other, once inflation between them equals light speed; and then they'd get closer and closer to traveling in opposite directions, as inflation between them tends towards infinity.

submitted by /u/dysthal
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Why do MRI machines require such extremely strong magnetic fields?

Posted: 20 Feb 2020 04:25 PM PST

Is it possible to send light into orbit?

Posted: 20 Feb 2020 08:38 PM PST

Forgive my ignorance, I'm not very smart in this area of science as far as astronomy/physics.

But I was thinking about how light can be bent when it goes around massive objects. If light can be Bent then if you were to get something with insane mass like a black hole, would it be possible to send light into orbit without letting it reach the event horizon?

submitted by /u/peepeehelicoptors
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How do air bubbles in a carbonated drink influence the volume of the drink?

Posted: 20 Feb 2020 04:37 PM PST

Hello,

so yesterday I was about to drink a drink that is heavily carbonated and I wanted to make it a bit more subtle bubblewise so I was about to shake the hell out of the bottle.

Before I've done that I began to wonder whether due to the shaking and bubbles leaving the drink will make the water drop a bit so since it was in a transparent bottle I marked where the water reached and shook it.

Once I've done that I noticed that the water level actually dropped but once I released the pressure and screwed off the lid it came back to it's original point.

I find this reaction quite an interesting one so I would like to know what makes the water drop and rise again since afaik the liquid is basically not compressable so it shouldn't drop enough to become that noticeable. Thank you

submitted by /u/czempi
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Does depression cause brain damage? Does it make you dumber?

Posted: 20 Feb 2020 02:33 PM PST

Is the Ethiopian Lion (Panthera leo roosevelti) a valid subspecies of lion or is it a part of Panthera leo nubica?

Posted: 20 Feb 2020 08:27 AM PST

The Ethiopian Lion is also known as the Abyssinian Lion or the Addis Ababa Lion. I'm reading so much conflicting descriptions online, so I'd love if an expert could chime in. Thanks!

submitted by /u/shawbin
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What's the difference between ultrasound and echocardiogram?

Posted: 20 Feb 2020 02:36 PM PST

1st year med student here. I understand the difference in use cases (ultrasound works anywhere, echocardiogram is specific to heart. ECG measures liquid flow, ultrasound is just an image, etc.) I'm confused about the technological differences. Is an echocardiogram based on ultrasound? The exact same machine? a completely different machine? Why is an echo so much more expensive than ultrasound? Is there any difference between a "cardiac ultrasound" and what you would see with echo?

submitted by /u/SanicDaHejog
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Why is the Pacific plate so flat?

Posted: 20 Feb 2020 02:07 PM PST

If you look at all of the continental plates, most of them have a significant amount of sub-aerial landmass. The only one that doesn't is the Pacific plate, which is almost entirely devoid of sub-aerial land. Why is this?

submitted by /u/Luke-P
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(pardon me for any mistakes, English isn't my first language)Why doesn't sodium move freely after giving chlorine an extra electron , i mean now both has a complete shell it should be free to move right? yet they seem to stick together as NaCl

Posted: 20 Feb 2020 03:21 PM PST

another question that i had which related to this topic is; once both of them have complete outer shells, why do we then refer to them as being charged? if, say, sodium has one extra electron and wants to give it out, then it'll be a positive ion, but after that it has given its electron to chlorine, why is it referred to as a positive ion even though now it has no charge

submitted by /u/ballsackoftitanic
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Is there any liquids floating in space?

Posted: 20 Feb 2020 01:52 PM PST

For example like a lake sized mass of liquid. If it's possible what would the liquid have to be the liquid form of since water would eventually freeze.

submitted by /u/Hazmat616
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How big can the gaps be in a faraday cage to still be functional?

Posted: 20 Feb 2020 11:15 AM PST

E.g. will a 1x1x1 km cube (only edges) protect against a lightning or electricity (230V 50Hz)?

submitted by /u/SoftLinkArmor
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Why are cases of dementia more common in North America and Europe compared to the rest of the world?

Posted: 20 Feb 2020 11:04 AM PST

How do forms of kinship descent pertain to a society's economic mode of production?

Posted: 20 Feb 2020 08:31 AM PST

When looking at patrilineal, matrilineal, bilateral, etc. forms of kinship descent, how are these cultural familial relations advantageous to certain modes of economic production? I know people don't form kinship rules out of boredom, so what motivates individuals to organize social relations in these specific ways?

submitted by /u/spudfolio
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How did the Deepwater Horizon oil spill get plugged up? Is it permanent, or will the containment method eventually erode away / break due to pressure?

Posted: 20 Feb 2020 06:44 AM PST

I just saw an add for Stelara a drug to treat Chrohns disease. One of the cautions was as follows: “Tell your doctor .... *if anyone in your house needs or recently had a vaccine*. Why would someone in your house NEEDING a vaccine or receiving one impact how a drug affects someone?

Posted: 20 Feb 2020 08:45 AM PST

I just saw an add for Stelara a drug to treat Chrohns disease.

One of the cautions was as follows: "Tell your doctor if you have an infection or flu like symptoms or sores, have had cancer or developed new skin growths or if anyone in your house needs or recently had a vaccine.

Why would someone in your house NEEDING a vaccine or receiving one impact how a drug affects someone or pose a risk?

submitted by /u/onepostonlyilied
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Are there moons with moons of their own?

Posted: 19 Feb 2020 09:43 PM PST

Are there any moons that have moons of their own? Is this even a theoretical possibility?

submitted by /u/muffireddit2
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How does ice skating work?

Posted: 20 Feb 2020 09:32 AM PST

I'm just curious because I have heard of a pressure melting theory

submitted by /u/xkxkxkxkxkx
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Why can’t we see stars on photos taken from the ISS?

Posted: 19 Feb 2020 10:37 PM PST

Why is mononucleosis (“mono” or “the kissing disease”) called mono-nucleolus?

Posted: 20 Feb 2020 10:45 AM PST

Thursday, February 20, 2020

Why is the Chernobyl New Safe Confinement only rated to last 100 years? What happens after 100 years pass? What determines how long it lasts?

Why is the Chernobyl New Safe Confinement only rated to last 100 years? What happens after 100 years pass? What determines how long it lasts?


Why is the Chernobyl New Safe Confinement only rated to last 100 years? What happens after 100 years pass? What determines how long it lasts?

Posted: 20 Feb 2020 05:41 AM PST

In July of 2019, the New Safe Confinement building over the remains of reactor 4 of Chernobyl was completed. It is the largest moving structure ever made by mankind, and it is designed to last 100 years.

But what happens after the 100 years are up? What determines how long the structure is to last for? Will it start leaking radiation in the final years of its life?

I'm flairing this as engineering, since I'm not sure what territory this falls under.

submitted by /u/EfficientSail0
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How does this work?

Posted: 20 Feb 2020 05:05 AM PST

If magma is lava that is under ground, does a volcano spew out magma or lava? When does magma become lava?

submitted by /u/GameIsMyName12
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Is the antarctic plate/continent magnetically attracted to the south pole?

Posted: 20 Feb 2020 01:06 AM PST

How small can an object be and still have a measurable gravitational pull?

Posted: 19 Feb 2020 11:43 AM PST

Can photon sieves reduce noise/background in epifluorescent microscope imaging?

Posted: 19 Feb 2020 03:41 PM PST

I read that scientists are using photon sieves to block unwanted 'light' and increase the resolution of telescopes in space. Can photon sieves, or something similar, be used in fluorescent microscopy to reduce light diffraction recorded by the camera sensor and increase resolution? Similar idea to space, but a different spectra of light. It kind of reminds me of confocal microscopy, but the spatial filter is placed later in the light path, if I understand it correctly. The penalty is a drastic cut in total light that reaches the sensor, but maybe it could be compensated by longer exposure times and averaging frames. I could see useful applications in biology. Thoughts?

submitted by /u/griffithsd
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How does negative and positive void coefficient work in regards to nuclear reactors?

Posted: 19 Feb 2020 05:58 AM PST

This is mostly in regards to Chernobyl, but could someone explain how a water-water moderator/coolant results in a positive void coefficient and how a water-graphite moderator/coolant results in a negative void coefficient? Perhaps I just don't know what the difference between a moderator and a coolant is.

submitted by /u/politics_user
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why is Eve from the bible named that way?

Posted: 19 Feb 2020 11:35 PM PST

in Hebrew, it sounds completely different from the way English people pronounce it.

submitted by /u/Marvellover13
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They say human brain is made-up of 100billion..how is this estimation made?

Posted: 19 Feb 2020 02:10 PM PST