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Tuesday, May 29, 2018

Does washing off fruits and vegetables before eating them actually remove much of the residual preservatives and/or pesticides?

Does washing off fruits and vegetables before eating them actually remove much of the residual preservatives and/or pesticides?


Does washing off fruits and vegetables before eating them actually remove much of the residual preservatives and/or pesticides?

Posted: 28 May 2018 10:07 PM PDT

Does radioactive decay reduce an object's mass?

Posted: 28 May 2018 10:25 AM PDT

I've been trying to understand e=mc2 and one implication of that seems to be that emitting radiation (energy) would mean that an object's mass decreases. At least on a theoretical level, maybe not measurably. Is this the case? If not, how can that be reconciled with the equation?

submitted by /u/ds1749320
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Is there a limit to how strong magnets can be? Or can we make stronger and stronger magnets with technological development/resources?

Posted: 28 May 2018 03:20 PM PDT

If there is a limit, what sets it? If not, what is needed for a stronger magnet?

submitted by /u/jonsins42
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How do firefighters put out fire on top floors of skyscrapers?

Posted: 29 May 2018 05:32 AM PDT

I mean, they can't possibly have 50-floor ladders

submitted by /u/Gaumir
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How do we know the percentages of life that were wiped out in mass extinctions?

Posted: 29 May 2018 07:27 AM PDT

I did a little digging in the sub(and Google) but couldn't find a question like this. How would we know that the Permian extinction wiped out roughly 90% of the planets population for example? From what I understand most of the fossilized remains we have recovered only represent a practically non-existent percentage of life that has existed throughout history. How can we even estimate current extinction rates, I haven't seen a list of the supposed dozens of extinctions occurring daily?(Though if they exist I would be very interested in seeing it)

submitted by /u/Dabaus94
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Can single-cell organisms get cancer?

Posted: 28 May 2018 11:40 AM PDT

After element 20, the neutrons begin to outnumber the protons in stable isotopes. Why do they need the extra neutrons?

Posted: 28 May 2018 01:00 PM PDT

If sunscreen absorbs UV light, does that mean that sunscreen makes you warmer?

Posted: 28 May 2018 02:34 PM PDT

I have read that what makes sunscreen work is partly that it absorbs UV light. As everyone knows, objects in colours that absorbs visible light gets warmer in the sun (like a black t-shirt). Does that mean that you get warmer in the sun with sunscreen than without?

submitted by /u/mountwebs
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Why is forming a chemical bond described as exothermic, whilst it appears to be endothermic?

Posted: 28 May 2018 10:16 PM PDT

Little bit of background info: Currently I study UK A-Level Chemistry and physics, so please don't expect too much.

Recently, when studying energetics (enthalpy changes, bonding, etc.) I noticed what appeared to be contradicting statements.

For chemical bonding, in terms of energetics, we are taught exclusively that bond breaking is endothermic, and bond forming is exothermic (in all cases).

This however contradicts other information that I have read in terms of bonding within carbon; that is that when carbon forms four covalent bonds, the electrons in the 2s sub-shell move to the (higher energy) 2p sub-shell making a hybrid orbital with four electrons.

If electrons move to a higher energy level to allow bonds to form, such an interaction would require energy to be taken in by electrons to be in an excited state, and therefore be endothermic.

It is taught in our syllabus however, that bond forming is exothermic.

I have no doubt that my syllabus is correct, but could someone offer an explanation as to why this is the case?

I asked both of my chemistry teachers, yet couldn't get an explanation, and searching the web fails to find specific enough results.

Footnote: Sorry about the formatting, and any grammatical errors, this was posted on mobile. and for the unrelated title, I really didn't know what to put considering the question mark was compulsory.

EDIT: Thank you all for all of the excellent quality, understandable answers, and I look forward to reading into this concept a little more after the school break as it does seem quite interesting.

submitted by /u/lasqi
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Can photons be slowed down by gravity?

Posted: 28 May 2018 02:01 PM PDT

If gravity can curve light, can it slow it?

submitted by /u/alonchalo
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Why does being exposed to radiation increase your chance of cancer in the future?

Posted: 28 May 2018 02:14 PM PDT

By this I mean, why does it increase your chances later in life and not just as soon as you are exposed

submitted by /u/PM_ME_BOXBOX_NUDES
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Why are both neutrons and protons required for stable nuclei (excluding hydrogen)? Why is there a more-or-less specific ratio between neutrons and protons?

Posted: 28 May 2018 02:57 PM PDT

And what causes instability in neutron-rich nuclei, if it's the protons that destabilize the nucleus due to electrostatic repulsion?

submitted by /u/unia_7
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Why can't we convert the kinetic energy of the tires spinning back into energy to charge the battery of electric cars?

Posted: 28 May 2018 05:51 PM PDT

Can a proton that is the result of beta minus decay undergo beta plus decay and the resulting neutron undergoes decay again and so on? If so, how many times?

Posted: 28 May 2018 09:12 PM PDT

Artificially/Naturally I understand that mass is converted into energy and if so, how many times can it happen?

submitted by /u/karrablaster123
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Is there a reason for the hexagonal pattern on the doors of microwaves?

Posted: 29 May 2018 03:26 AM PDT

Or is it just better if we don't see what's in there 100% clearly?

submitted by /u/endisnearhere
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If a molecule can only have fixed energy levels then why is a Boltzmann distribution a smooth curve?

Posted: 28 May 2018 01:12 PM PDT

Hi, If a molecules energy level is quantized, why does a Boltzmann distribution look like this: http://noyesharrigan.cmswiki.wikispaces.net/file/view/MD_distribution.png/250991340/MD_distribution.png

and not a linear distribution?

submitted by /u/Box_xx
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Was it possible to see the first moonlanding via a telescope on our planet?

Posted: 28 May 2018 12:46 PM PDT

If a nuclear apocalypse were to happen, and every single nuclear weapon in the world was used, how long would it take for the accumulating fallout to decay and make the surface habitable?

Posted: 28 May 2018 06:32 PM PDT

Why are weather patterns so different in different parts of the United States?

Posted: 28 May 2018 02:15 PM PDT

I don't mean so much the climates, rather the manifestation of weather. On the East Coast, it will rain for days on end, while in the desert, in the West, it will rain very hard for about half an hour and then it will be sunny for the rest of the day. What factors cause such a difference in the way that weather occurs?

submitted by /u/ChezKicks
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Do large nuculii extend beyond the range of the strong force?

Posted: 28 May 2018 12:44 PM PDT

Why do storms develop after a hot day? And why do these storms sometimes get forecast but then seem to get pushed back later and never end up developing?

Posted: 28 May 2018 12:35 PM PDT

Self-explanatory title, but I just wondered because we have had a few hot days in the UK, and each day a storm has been forecast for early-mid afternoon. Then by the time it gets to midday it is pushed back later, and later.. what makes it so difficult to predict when/if a storm will develop after a hot day?

submitted by /u/SublimelySublime
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Could electromagnetic power be transmitted over long distances as magnetic flux instead of electric current?

Posted: 28 May 2018 09:09 PM PDT

My understanding of electromagnetism isn't as complete as I would like, but as I understand it, magnetic flux would rather be contained within ferromagnetic material than in the dielectric surrounding it, which seems like it should be better for power transmission than electric current which is in the dielectric surrounding the electric conductor. This difference makes it seem like the magnetic flux "resistance" (or what is the correct term?) of a ferromagnetic wire or chain should be lower than the resistance of electric wire.

The flux might be alternating, rotating or possibly even both alternating and rotating depending on what is able to be transmitted most efficiently.

It seems like at least one big advantage of using magnetic flux instead of electric current would be in the use of cheap iron wire or chain rather than more expensive aluminum, copper or copper-plated electric wire.

I assume someone must have already thought of this if it really is a viable idea, so what am I forgetting?

submitted by /u/dalkon
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Monday, May 28, 2018

How come when hot metal is placed in cold water, it does not shatter like glass?

How come when hot metal is placed in cold water, it does not shatter like glass?


How come when hot metal is placed in cold water, it does not shatter like glass?

Posted: 27 May 2018 10:36 AM PDT

Can metals evaporate? If so, can the gas be condensed back into solid metal?

Posted: 27 May 2018 11:45 AM PDT

How does Vitamin D absorbed from the sun vs. orally supplemented Vitamin D affect the human body?

Posted: 27 May 2018 01:06 PM PDT

I've heard that Pangaea didn't have much in the way of mountain ranges, but shouldn't a supercontinent comprised of plates that smashed together have some massive mountain ranges? How do we know one or the other is true?

Posted: 27 May 2018 09:06 AM PDT

Why do amputated body parts not grow back even if bones can heal themselves?

Posted: 27 May 2018 08:11 AM PDT

Does everything emit radiation?

Posted: 27 May 2018 04:01 PM PDT

https://en.m.wikipedia.org/wiki/Planck_temperature

This makes it seem like everything thar isnt at absolute zero emits radiation, and we can measure the temperature of an object by measuring the wavelength of the light it emits

Can I put a person in some kind of faraday cage and take their surface temperature by measuring the amount/quality of EM energy they emit?

Can I measure the temperature of a light bulb based on its color?

submitted by /u/jehan60188
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Why can't your immune get rid of bacterial STDs like syphilis etc?

Posted: 27 May 2018 09:23 AM PDT

Since cats don't sweat/perspire; Does moving air, from a fan for instance, cool them off in hot weather?

Posted: 27 May 2018 12:00 PM PDT

Do large asteroids impacting Jupiter reach the surface or do they begin swimming in the thick atmosphere at a certain altitude?

Posted: 27 May 2018 12:53 PM PDT

With Juno amazingly confirming the clouds of Jupiter to go as far as 3000km down, I was wondering if an asteroid could actually reach the surface or if it would be stopped by the increasingly dense clouds on Jupiter.

submitted by /u/zebleck
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What happens to the bullets that are shot into the air?

Posted: 27 May 2018 02:06 PM PDT

They surely fall down after a while right? If correct, they can easily cause damage or even harm to someone

submitted by /u/frey1337
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Are electric and magnetic fields made out of photons (since the photon is the force carrier)? If so, why aren't those fields affected by a physical barrier like visible light is?

Posted: 27 May 2018 04:01 PM PDT

Photons are force carrier particles that carry the electromagnetic force; if so, how come those fields aren't affected by a physical barrier? I've heard that fields aren't made out of anything, but I've also heard that they are an exchange of particles.

submitted by /u/qwerty-_-123
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How do nutritional scientists empirically test if certain types of food are "healthier" than others (e.g. white vs brown rice)?

Posted: 27 May 2018 12:28 PM PDT

How did scientists measure the speed of light?

Posted: 27 May 2018 08:03 AM PDT

With the speed of light being so fast, how do scientists measure it? I would think the instruments we use now wouldn't be able to detect something moving that fast.

submitted by /u/ivaldx
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Why do we tear up when we laugh too hard?

Posted: 27 May 2018 10:10 AM PDT

Why do we "lose our appetite" when we see things we find disgusting, or otherwise unappealing?

Posted: 27 May 2018 09:53 AM PDT

Has a link been found between red meat and heart disease in any mammal other than humans?

Posted: 27 May 2018 05:05 AM PDT

There are many obligate carnivores that eat red meat almost exclusively. Can this diet cause heart disease? And if not, what are the adaptations that humans do not have?

submitted by /u/platypus_stalker
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How does the body signal beard follicles to start growing and why does it sometimes happen after puberty?

Posted: 27 May 2018 09:00 AM PDT

Does Bell's inequality rely on photon polarisation being undefined before measurement rather than simply unknown?

Posted: 27 May 2018 09:27 AM PDT

My reading of EPR is that simple values such as momentum must have a value even when not measured, which flies against the uncertainty principle and wavelike nature of particles.

I've tried reading Bell's papers and subsequent ones and I can't tell whether they rely on the photon having an uncertain polarisation before measurement, but a hidden variable defining the outcome of the measurement, rather than an unknown polarisation before measurement and the outcome of the measurement being probabilistic.

Can someone point me to anything that helps me understand this better?

submitted by /u/yeast_problem
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I understand why transition metal compounds have different colours and flame tests, but why are pure metals like copper, gold, and iron diffierent colours?

Posted: 27 May 2018 07:39 AM PDT

If you bailed out of an airplane flying at supersonic speeds would the wind rip off or burn off your skin?

Posted: 27 May 2018 04:29 AM PDT

Sunday, May 27, 2018

If the universe is (generally speaking) flat, how come, as seen from telescopes, nothing lies on a single plane? Images of the CMB aren't 3D models, so why do we see galaxies in every direction?

If the universe is (generally speaking) flat, how come, as seen from telescopes, nothing lies on a single plane? Images of the CMB aren't 3D models, so why do we see galaxies in every direction?


If the universe is (generally speaking) flat, how come, as seen from telescopes, nothing lies on a single plane? Images of the CMB aren't 3D models, so why do we see galaxies in every direction?

Posted: 26 May 2018 03:35 PM PDT

Is the speed of gravity constant?

Posted: 26 May 2018 05:03 PM PDT

So I know that gravitational waves travel at the speed of light (in a vacuum) but are there circumstances where the speed of gravity changes? If so what are these circumstances?

submitted by /u/The_Rickest-Rick
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How I can I picture a radio wave in 3d space?

Posted: 26 May 2018 03:58 PM PDT

I only ever see them depicted as sine waves online, but my guess would be that 'sine waves' are to radio waves as what '12' is to a carton of eggs.

Is it possible to picture how they are around me in my environment?

submitted by /u/browngirls
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How did terrestrial animals and insects like Mongoose and Spiders get to islands far from land like Hawaii or Guam?

Posted: 26 May 2018 11:14 AM PDT

Supermassive black hole accretion rates, are they constant?

Posted: 26 May 2018 04:28 PM PDT

This article: http://www.astronomy.com/news/2018/05/snapshot-second-gaia-release-results-so-far states that we have found a supermassive black hole of 20 billion solar masses 12 billion light years away that is accreting at the rate of 1% every million years.

That rather sounded like a compound interest statement, so I plugged the numbers into a calculator to figure out how large it would be after 12 billion years (now), and got 143,719,397,330,047,128,616,744,826,647,657,321,145,325,176,127,225,856 billion solar masses.

That seems like a lot. Do we expect it to have stopped it's accretion at some point, or is the article miss-stating that fact (it also breaks it down as solar masses per day).

Also, what's the Schwarzschild radius of something that massive?

submitted by /u/voidref
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If sex steroids pass through all cells, how can only one follicle be matured and one egg released at a time for women in the menstrual cycle?

Posted: 26 May 2018 11:27 AM PDT

What is “Cosmic Background Radiation”?

Posted: 26 May 2018 11:34 AM PDT

Are (metallic) superconductors good mirrors?

Posted: 26 May 2018 09:31 AM PDT

I recently gained the insight that mirrors work because the electrons in the metal sheet, when an photon hits, move until their electric field is equal in strength to the photons electric field, creating the reflected oscillating field- a reflected photon. The electrical resistance of the material hampers this flow to create an opposing field. So I wonder whether superconductors, having no resistance, are mirrors, and if they are, how good they are? Are all superconductors mirrors, or only ones made of specific materials? Do they reflect all wavelenghts equally?

TL;DR: Learned resistance makes mirros worse, asking if superconductors are great mirrors.

P.S. If you find my english objectionable, not my first language.

submitted by /u/MoeWind420
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Can you squeeze an electron?

Posted: 26 May 2018 08:22 AM PDT

Can you squeeze an electron and make its volume smaller?

This question came into my mind when I've heard that "If you remove all the space in the atoms, the entire human race could fit in the volume of a sugar cube". But to create a black hole, you would need to compress them in a smaller volume. So the conclusion is : black holes suqeeze electrons/protons. Is this true?

submitted by /u/Zapakitu
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Do Bees differentiate types of pollen/show a preference for one type of flower over another or is it all functionally the same to them?

Posted: 26 May 2018 11:56 AM PDT

In the many-worlds theory of QM, is there a theory of how many universes branch of from a single quantum observation?

Posted: 26 May 2018 06:22 AM PDT

Here are 3 examples that getting answers for might clear things up.

First is a fundamental uncertainty: let's say the universe consists of one electron, whose spin equally likely up or down. You observe it. Does the universe branch into two universes, one for each option? Or infinite universes, with half at spin-up and half at spin-down?

Next is a case where maybe the outside world matters: Let's say there's an electron, and an potential barrier, and the electron has a 50% chance of tunneling through it. When you observe it, does the universe split into two branches? Or infinite?

Finally, let's say the same electron has some irrational chance of tunneling through (lets say sqrt(3) chance). When you observe it, what exactly happens? I can't see how the universe would split into a finite amount of states after this.

The reason I ask about spin AND tunneling is, I don't know if many-worlds reasoning only applies to fundamental observations, or system-observations.

As a follow-up question: when people who know what they're talking about think about this stuff, do they picture universes being created for each decision, or two universes that were sitting on top of each other to begin with, diverging?

submitted by /u/asdfwaevc
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What size/speed/density would a meteor have to be to fly through Jupiter?

Posted: 26 May 2018 04:24 AM PDT

Do the laws of thermodynamics apply to subatomic phenomena?

Posted: 26 May 2018 05:53 AM PDT

I was studying thermodynamics for my materialsscience course and I started to wonder.

It is assumed in thermodynamics that energy is constant but I guess you could look at the fission of a nucleus as chemical reaction. Not sure, what do you think?

submitted by /u/RadChad14
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Why do height requirements exist for some rides and what studies have been done to determine the standards?

Posted: 26 May 2018 09:50 AM PDT

Does every closed system have a maximum and minimum value of entropy?

Posted: 25 May 2018 11:00 PM PDT