Physics Discussion Thread

Vayutuvan · Post by **Vayutuvan** » 08 Oct 2013 23:03

At least what I remember is that SLAC people got a Nobel before Salam, Weinberg and Glashow. If that is correct, then it is a case of experimental people getting before the theoreticians. Were these two back-to-back prizes connected as intimately as this year's prize and CERN? May be CERN will get it for a whole lot of related/unrelated experiments. Did they get a Nobel yet?

Amber G. · Post by **Amber G.** » 09 Oct 2013 01:37

Some may like this..Higgs boson in simple terms ...

Amber G. · Post by **Amber G.** » 09 Oct 2013 01:44

Here for more serious people, it is explained in one (or little more) minute..

Enjoy:

Bade · Post by **Bade** » 09 Oct 2013 01:47

matrimc, I don't think they have given a Nobel to an institution in Physics at least, unlike peace prizes.

Carlo Rubbia and Simon Van der Meer were the last CERN guys to get it. That was for W,Z discovery.

SaiK · Post by **SaiK** » 09 Oct 2013 01:57

might as well stay with god concept!

Bade · Post by **Bade** » 09 Oct 2013 02:18

^^^ That is for the paranormal thread.

Only normal thoughts allowed here.

SaiK · Post by **SaiK** » 09 Oct 2013 02:25

i mean, higgs boson is not after all god right? it excludes gravity

btw, why only higgs got nobel and not our sathyendra bose? not fair!

Mort Walker · Post by **Mort Walker** » 09 Oct 2013 05:06

Bade wrote:^^^ That is for the paranormal thread. Only normal thoughts allowed here.

Are you talking about the metaphysics and astrology dhaaga?

Bade · Post by **Bade** » 09 Oct 2013 05:47

I guess, yes.

Vayutuvan · Post by **Vayutuvan** » 09 Oct 2013 06:57

SaiK, Nobel cannot be awarded posthumously. The rumor was that they were about to relax a couple of times - for Gandhi (peace) and for von Neumann (let me call him JVN for short) (?) (economics). JVN's work in all areas (Math, Physics, Applied Math, Computers) is far reaching and widely applicable. Same with MKG.

Bade · Post by **Bade** » 09 Oct 2013 07:12

SN Bose's work has no direct connection with Peter Higgs et al. It just happens to be a Boson and not a fermion so to speak. Higgs particle is not the only Boson, and any particle with an integer spin is also called a Boson like the photon.

SN Bose or for that matter MN Saha did exceptional work, and both of them deserved to get it IMO just like Raman from that era.

Philip · Post by **Philip** » 09 Oct 2013 07:14

This post has used "escape velocity" to transfer elsewhere in the BR cosmos!

Bade · Post by **Bade** » 09 Oct 2013 07:17

^^^^

I do not see how this is relevant for this thread. Better stick it in Modi thread for all the pindi-mentalists.

SaiK · Post by **SaiK** » 09 Oct 2013 07:23

phillip thoda higgs-boson cocktail piya hoga.

so pooch time.. does higgs-boson particle travel at >= 'c' ?

Vayutuvan · Post by **Vayutuvan** » 09 Oct 2013 08:06

Drop the > sign. Even equality may be a question mark. Maybe mass less particles can (otherwise as v -> c, m -> infinity and l -> 0 - Lorenz contraction).

Bade · Post by **Bade** » 09 Oct 2013 08:43

Basically it will require an infinite amount of energy to accelerate a non-zero mass particle very very close to the velocity of light. So not possible !

johneeG · Post by **johneeG** » 09 Oct 2013 12:03

SriKumar wrote:
johneeG wrote: Saar,
in your example, bus moves because the bus is in contact with the road. There is a friction between road and bus tyres. .....
Tires or no tires, the bus' final velocity will be unchanged (or zero, if the bus is stationary to start with). Assume that the bus is stationary to start with. When a person moves forward, the bus will move back a bit in response to the person pushing it backwards. The person accelerates forward, and the bus accelerates backwards in response (tires or no tires). When the person hits a front wall in the bus, it will stop the bus. The momentum of the bus and the person will balance out. But forget this example, it just confuses the matter.

I am unable to understand what you are saying. Where exactly is the bus situated in your example? What is the environment of the bus?

SriKumar wrote: Check the link you provided.

There is a clear reason the overall container will not move, even though the gas is escaping. The reason is that escaping gas molecules will not create an _unbalanced_ force (which is needed to make the chamber move). Because when the gas molecules come out with a certain velocity (and therefore momntum) they hit the wall of the _same_ container that they came out of. Check the diagram. There are 2 chambers but both chambers are in one container.

The example in your link is _not_ analogous to the original situation you are trying to prove (even though the gas is indeed escaping from a pressurized chamber into a vacuum chamber). It is not analogous because after release, the gas still sits inside the same container.

As soon as the nozzle is open, the gas escapes and the chamber becomes vacuum. The gas that escapes does not do any work. This is called 'Free expansion'. Secondly, once the gas escapes into the vacuum, they should be seen as individual molecules, not as gas. Because gas is only defined in pressure. Once there is no pressure(in vacuum, there is no pressure), then the gas is not defined.

Because the gas escapes as soon as the nozzle is opened, the combustion is not possible. So, how does the rocket move without combustion?

Theo_Fidel wrote:I don't know anyone who seriously expects that we will ever understand everything. This is the classic fish bowl problem. And we are stuck inside the fish bowl. The entire dark matter thing was only revealed recently due to oblique information that did not match up. We can only interpret what we can detect.

You mean regardless of how many years people devote to understanding the world, people will never be able to understand it completely?

Ok, fine. If people cannot understand the universe completely, can they the people at least understand the fundamental concepts guiding the universe, or is this also not possible according to you?

Bade wrote:When people start equating physics with philosophy and slowly by extension with religion, I know we have a big problem. But then it is not my problem. It is up to the people who constructs such connections to clear their own cobwebs.

I think the issue with you is that you are stuck with the labels instead of concentrating on concepts or content. You are like,"this is 'physics', so it must be true. This is 'philosophy', so it must be in such a manner. This is 'religion', so it must be bogus. ....etc"

You are only looking at the tags. As for me, I am only concerned with the truth or reality(whatever that maybe). Religion, science, philosophy,...etc are all talking about the same thing. If they differ with each other, then one of them must be correct while others must be wrong.

Anyway, I wrote an elaborate post giving a step by step way of my conclusion. If there was something that was not correct or rational, then you can easily pinpoint it. That would be immensely helpful in clearing the cobwebs, if they exist.

In fact, this is a great opportunity to you. I see that in many of your posts you speak disparagingly about religion or philosophy. I gave you an opportunity by elaborately posting to thrash that point of view. Instead of doing that, you are posting a very lazy and biased comment.

Generally, with short posts(or comments), it is difficult to make criticisms. But, with long elaborate speeches or posts, one opens up oneself to all kinds of attacks from all sides. Because one betrays one's mistakes when one speaks for long. So, I opened up myself to any criticism by posting that post here. You could rip it up to pieces if you think it deserves that.

Link for a post that compares the modern science with religions

Bade · Post by **Bade** » 09 Oct 2013 18:02

^^^ One does not need long elaborate posts if the content is meaningful. Of course a lot of things cannot be put in words. If anyone can do that with current formalism of say General Relativity then they deserve accolades. I have not come across any so far. I am not talking about popular articles on the subject, but the full mathematical formalism. So to understand one really has to learn the math.

But someone like you come around and make statements with no basis. It all sounds well and logical in English, but it is just that. It does not mean anyone has understood your statements any better.

Your statement on religion, philosophy and physics being the same thing is laughable. Can you verify the concepts of religions with any independent experimental proof ? Less said about philosophy the better. Religion at best can be described as codified or fossilized philosophy. Physics has no such codes. If you fail to see the difference, no one can help you understand it better. You are free to live in your delusional world, a world which a lot of physicists are not willing to accept as close to reality.

And if you believe physics is not a complete understanding, well you can ignore it...but then people like you who harbour these ideas want to hitch to any statements of physics and want to draw a parallel in religion or philosophy and claim it. Good luck and I at least am not buying it.

SaiK · Post by **SaiK** » 09 Oct 2013 18:07

does that mean, a negative mass particle existence can be proved?
context: non-zero mass

Bade · Post by **Bade** » 09 Oct 2013 18:13

No experimental proof exists for negative mass particles as far as I know.

Amber G. · Post by **Amber G.** » 09 Oct 2013 22:07

JohneeG - (and others)

Much more than long posts, I will be more interested if you can reply/comment on any of the ordinary problems I posted at:
http://forums.bharat-rakshak.com/viewto ... 8#p1521388

That can show much more about understanding of some basic principles of physics and one can learn much more.... What's more, one need not use big words and talk about stress tensors and general theory of relativity ..

Let us see if any one here is willing to answer/discuss these questions. None of the questions require more physics than one learns in UG level. (And some of these are related to some of the issues we have recently discussed here)

Amber G. · Post by **Amber G.** » 09 Oct 2013 22:42

Let me comment on a very interesting aspect (physics vise) of a discussion related to "falling bullets) .. (Please read the following quote and a few messages above and below for context)

Bade wrote:matrimc, you would need a infinitesimally small cross section, but at the same time a large mass to reduce the effect of drag. This leads to the necessity of a thin infinite wire to accommodate more mass. But then the even this will have a large surface area along the sides which will experience drag too. Only way to minimize the effects of the drag then, is to make sure it falls vertically down, otherwise the cross sectional area will change depending on tilt.

Anyway, the best is to make plots of Vt vs mass and A and look for surface minimum to get the smallest Vt possible to look for the opposite effect of least K.E. for safe bullets, so that abduls can fire in the air merrily without too much concern.

Newton himself noticed and wrote about it, and so did quite a few others. (And I have seen it being discussed in a few advance physics classes)

Interestingly the range of a bullet (or an arrow, or a spear for that matter), at first approximation, depends mainly on length and little on the muzzle velocity.

(Shape and density of projectile matters, but these aspects are fixed by other considerations)

It may sound strange, but it is correct. Even if you double the muzzle velocity of a bullet in a typical rifle (keeping other aspects the same) the range of the bullet will remain practically the same!

What's more, assuming the bullet is made of lead (or any one particular material) the range, as a first approximation, depends mainly on the length of the bullet!

(This is why torpedoes (or arrows or spears shot by a spear-gun) are long.. )
(This is why bullets in a long range rifle are longer than bullets in hand guns)

(BTW, The equation given by Bade, a few posts above, also make that aspect clear

)

Theo_Fidel · Post by **Theo_Fidel** » 09 Oct 2013 22:48

johneeG wrote:You mean regardless of how many years people devote to understanding the world, people will never be able to understand it completely?

Ok, fine. If people cannot understand the universe completely, can they the people at least understand the fundamental concepts guiding the universe, or is this also not possible according to you?

Saar,

I have devoted my life to a teeny tiny area of struc. engineering and I still don't know everything. Every year new things are found and commonly understood rules are over turned. And this is with fully deterministic systems and fully repeatable testing to destruction. Even then there are failure modes that are not repeatable and pop up spontaneously. So you have to understand I'm a little more uncertain about these things.

There is only one universe. You can not test it to destruction. So now tell me how you plan to understand it. I have one simple question for you why is the mass ratio between an Electron and a Proton = 1,836.152672....
Why not 1,835.152672...

We only know some of the rules the universe follows. Nothing fundamental has been shown to us AFAIK. We don't even know what quarks are though we can mathematically organize them. I think understanding is beyond us mortals. Only thing available to us is some small glimpses of reality. The double slit experiment is one such glimpse of reality. The Higgs discovery is another such glimpse if less enigmatic.

To give you an idea of how little we know, recently there was a paper describing how the universe could be a 3-D hologram of a 2-D structure projected into our space. Incredibly this solution was found to be largely mathematically consistent with what we observe. Now this does not mean the universe is really this way but it only reveals our ignorance and almost total lack of understanding.

Take another item Time. We have no idea what it is. Quantum mechanics makes no use of it. Yet we are sure it exists and relativity says it is woven into the fabric of space itself. So what sort of understanding is possible without understanding time.

Amber G. · Post by **Amber G.** » 10 Oct 2013 00:20

venug wrote:
And yes gravity assisted sling-shot trajectories are planned for space flights to observe Sun for example, don't remember the name of the spacecarft, but they wanted to use the gravity of Saturn(?) to 'sling' the spacecraft into Sun's orbit...interesting stuff.

Gravity assisted sling-shot trajectories are more routine (for both braking and accelerating purposes)
For example this from today's news..
Juno probe SCREAMS past Earth on way to JUPITER

NASA's Juno spacecraft is about to say goodbye to Earth with a flyby designed to give it a 12,000 km/h speed boost on its way to Jupiter. And as a test of one of its experiments, radio hams are invited to get together and say “hi” to the probe. Juno

member_22872 · Post by **member_22872** » 10 Oct 2013 01:01

AmberG ji, one question, in the case of long ranges like that of sniper rifle bullets, won't aerodyanmic design also have a say on the range? some bullets might even enter supersonic speeds and shocks can dampen the speed hence the range of the bullet? and angular velocity imparted to some bullets might increase the heat dissipation as well.

Theo_Fidel · Post by **Theo_Fidel** » 10 Oct 2013 01:16

Venu,

WRT range, look up the Thunder Well incident. The understanding is the plate was launched out of the Solar system!! Though there are skeptics.

http://en.wikipedia.org/wiki/Operation_Plumbbob

member_22872 · Post by **member_22872** » 10 Oct 2013 01:46

Theo (I apologize, to me without a ji sounds rude), very interesting, but in the case of the plate, assuming a sound speed of 330m/s, it is clearly in hypersonic regime. I am not sure why they even assumed that the plate would survive a 200 mach flow where high surface temperatures would dominate once it hits the atmosphere. This is also the reason as you might already know for heat shield on the shuttle and reentry vehicles which are subjected to 20-25 mach flows(approx). But in case of the bullet even though it might not experience such high temperatures, drag could play a role...me thinks.

member_22872 · Post by **member_22872** » 10 Oct 2013 02:21

AmberG ji, my attempt at Q1:

1) If one sleeps under a tree, one will not get wet from morning dew. (or not as wet as if one sleeps under open sky)
Because the tree:
a) Absorbs star light
b) Keeps air from rising
c) Emits infrared radiation
d) Blocks the clouds
e) Tree is older than Chernobyl, hence it absorbed all radioactive Cs and produces heat
f) No, it is not true, you get almost as wet..

C seems to be making sense. The reason being the C3/C4 of plant respiration cycle would mean more CO2 at night emitted by trees. CO2 absorbs and emits IR, thus local temperature increase leading to evaporation of dew droplets?

member_22872 · Post by **member_22872** » 10 Oct 2013 02:27

P2 A nuclear reactor cannot explode like a nuclear bomb because
a) It contains too much Uranium
b) It contains no uranium
c) Nuclear reactor depends on slow neutrons
d) It is carefully designed to shutdown quickly
e) None of the above, on average there is one explosion every year
f) Not e) but there were a few in Fukushima.

neutrons slowed by moderators.

Theo_Fidel · Post by **Theo_Fidel** » 10 Oct 2013 02:34

Thanx for not using Ji.

The camera caught it intact out of the well and the lower bound is 66km/s. The fastest object ever on earth! I agree vaporization is most likely but there is a small chance it got through. There are calculations that show that large objects that ablate will get through. It would only spend about 1 Sec in the bulk of earths atmosphere.

Don't want presume about Amber but I think she is talking about range not accuracy or Ballistics. Beyond certain velocities the atmospheric drag is more or less fixed, no matter the shape, the object will 'forcibly' streamlined. Bullets are shaped the way they are for ballistics and penetration. This is what a rail gun projectile looks like. It depends on pure kinetic energy for kill power. Obviously it does not look like a bullet.

negi · Post by **negi** » 10 Oct 2013 02:46

2 A nuclear reactor cannot explode like a nuclear bomb because
a) It contains too much Uranium
b) It contains no uranium
c) Nuclear reactor depends on slow neutrons
d) It is carefully designed to shutdown quickly
e) None of the above, on average there is one explosion every year
f) Not e) but there were a few in Fukushima.

I think 'c' is the right answer but I have a question on this subject.

While conventional nuclear reactors require slow neutrons for initiating and sustaining nuclear fission , how does fast neutron then cause a fission in a U-235 pit used in an atom bomb ? Does the high % of U-235 in the pit as against a low % of U-235 in the fuel rods has something to do with this, how do I get to visualize this with some equation ?

negi · Post by **negi** » 10 Oct 2013 02:53

P3. Plutonium can explode with fewer generations than can Uranium because:
a) Plutonium fission releases more neutrons
b)Pu fission releases more energy
c)Pu does not require moderator
d)Pu turns into Uranium

johneeG · Post by **johneeG** » 10 Oct 2013 03:02

negi wrote:2 A nuclear reactor cannot explode like a nuclear bomb because
a) It contains too much Uranium
b) It contains no uranium
c) Nuclear reactor depends on slow neutrons
d) It is carefully designed to shutdown quickly
e) None of the above, on average there is one explosion every year
f) Not e) but there were a few in Fukushima.

I think 'c' is the right answer but I have a question on this subject.

While conventional nuclear reactors require slow neutrons for initiating and sustaining nuclear fission , how does fast neutron then cause a fission in a U-235 pit used in an atom bomb ? Does the high % of U-235 in the pit as against a low % of U-235 in the fuel rods has something to do with this, how do I get to visualize this with some equation ?

Critical mass which is made up of target ring and projectile ring. Both these rings are made up of U-235. These two rings together form the critical mass of uranium. The critical mass is the least amount of Uranium required to initiate a chain reaction in a nuke bomb.

Some say, all that is nonsense and that nuke bombs don't work. Eg: Link

1) If one sleeps under a tree, one will not get wet from morning dew. (or not as wet as if one sleeps under open sky)
Because the tree:
a) Absorbs star light
b) Keeps air from rising
c) Emits infrared radiation
d) Blocks the clouds
e) Tree is older than Chernobyl, hence it absorbed all radioactive Cs and produces heat
f) No, it is not true, you get almost as wet..

hmm... I never thought about this.

I read somewhere that trees release CO2 in the night and take in O2. CO2 increases greenhouse effect that means it retains the heat from the sun, if I am not wrong.

It seems clear skies are needed for the formation of more dew.

I think b), c) & d) are correct. But, strictly speaking I don't know about this one. Maybe f) is also true. I need to read up on this one.

I guess it depends on the kind of tree...

member_22872 · Post by **member_22872** » 10 Oct 2013 03:07

Theo, I think, even though it spends just 1 sec, very high temperatures, thousands of Kelvin could evaporize the plate...you already know our sun's surface temperature is 6000C and no metal exists may be even beyond 2000C in solid form. On the other hand few meteorites survive renetry, that could mean that their speeds are much less, but with 1 sec, yes you could be right, there is a slight chance to assume may be they would be able to catch it on film burning( but again, you wink and it's lost). It is at times difficult to fathom the magnitude of temperatures and what it can do to metal.

There was a program on NG, where they talked about iron rain on a planet as iron evaporated at planet's surface temperatures vaporizes iron and it rains molten iron when it condenses.

negi · Post by **negi** » 10 Oct 2013 03:07

P5 Professor Anwar Jamaal Kidwai (in the movie Ek Tha Tiger) walks a dog. The dog (weighing 52 pounds)
pulls on the leash, (pulling AJK), with a force of 200 N . According to Newton's third law, equal and opposite force of 200N is applied by the leash on the dog. In the movie we see that dog does move.This is is best explained by:

Answer: I think this is best explained by Newton's second law of motion because all the forces acting towards the dog are not balanced.

negi · Post by **negi** » 10 Oct 2013 03:16

JohneeG your response does not answer my question even after a critical mass is formed essentially what is happening is a neutron is causing an atom of U-235 to split/fission and they are not being moderated as such , my question is why do the energy levels of a neutron have to be different for fissioning a U-235 atom in a conventional reactor vs a fission weapon ?

member_22872 · Post by **member_22872** » 10 Oct 2013 03:17

While conventional nuclear reactors require slow neutrons for initiating and sustaining nuclear fission , how does fast neutron then cause a fission in a U-235 pit used in an atom bomb ? Does the high % of U-235 in the pit as against a low % of U-235 in the fuel rods has something to do with this, how do I get to visualize this with some equation ?

Please entertain this nanha wannabe's soch:
To make a nuke reaction go critical you need 1. Enough fast Neutrons 2. Short half life and enough Radio active material.

More neutrons means more reactions. Fast neutrons means high KE enough to sustain nuclear transmutations to another fast half life radio active material like U235...in case if reactors, moderation is done to reduce the number of neutrons and/or slowing down the neutrons...in case of A-bomb no control exists once it is initiated.

negi · Post by **negi** » 10 Oct 2013 03:29

venug wrote:in case if reactors, moderation is done to reduce the number of neutrons and/or slowing down the neutrons...in case of A-bomb no control exists once it is initiated.

In case of a conventional reactor number of neutrons are controlled by control rods basically keeps the effective neutron multiplication factor under check; their energy is what is reduced by a moderator . My question is in a gun type device we have a neutron source or initiator so it releases a neutron just like it would in a reactor so why won't that neutron/neutrons need to be slowed down ? (Please note there have been fission type atomic devices tested which employed use of moderators)

On second thoughts there are neutron deflectors in a fission weapon so in theory if a lot of neutrons are produced in short span of time they will collide with each other and if these are inelastic in nature these neutrons should slow down .

member_22872 · Post by **member_22872** » 10 Oct 2013 03:37

I think it boils down to design, how much slowing you need to have a desired effect...and if slowing is necessary at all. What use is a nuke, when if time to react is very small( in terms of Tdetonate-Trelease) for example.

member_22872 · Post by **member_22872** » 10 Oct 2013 03:40

In fact no collision is elastic ever. There is always energy and momentum loss.