The h Bar

Akash. B

5:17 AM

hi

John Rennie

@Akash.B morning :-)

Akash. B

@JohnRennie same to you

@JohnRennie can you give me a career guidance ?

John Rennie

@Akash.B I'm not especially qualified to give advice with careers, but I'm happy to listen if you have concerns ...

Akash. B

@JohnRennie I want to be a physicist

John Rennie

How old are you at the moment - if you don't mind answering, I'm only asking to judge what stage of school you're at

PM 2Ring

5:28 AM

@PranshuKhandal I suppose it might be possible to do magnetic levitation if the upper magnet's centre of mass is below the centre of the lower magnet, like the classic balancing trick involving a needle, a cork, and two forks:

Akash. B

@JohnRennie I will be 16 by July 21

John Rennie

I really, really wanted to be a physicist when I was your age. In fact I had wanted to be a physicist as far back as I remember, even as a really small child.

PM 2Ring

John Rennie

But looking back, at that age I had no idea what physicists actually did. I guess I just thought it seemed fun.

Akash. B

@JohnRennie what made you interested in physics?

@PM2Ring hmm this seems familiar

John Rennie

5:32 AM

@Akash.B because it explains how the world works. Remember that this was about the time men first walked on the Moon, and space travel seemed really exciting. Also I read lots of science fiction and really wanted to build a hyperspatial drive.

(I never did build a hyperspatial drive. Oh well.)

PM 2Ring

@Akash.B Here's a similar thing involving a hammer & a wooden ruler:

37

Q: Hanging a hammer from a table and a stick so that its midpoint is outside of the support of the table

I came across this pic on the internet today. At beginning I thought it is just not possible because the centre of mass is way off so gravity will generate torque making the stick and hammer fall. Later I thought that the heaviest part of hammer could've balanced the centre of mass and so it co...

John Rennie

@PM2Ring ooh, I must try that! :-)

Akash. B

@JohnRennie how was your marks in mathematics ?

John Rennie

@Akash.B right from an early age I got top marks in maths.

PM 2Ring

It's totally possible; I just replicated it. — PM 2Ring Jan 26 '17 at 13:40

John Rennie

5:36 AM

@PM2Ring :-)

Akash. B

@JohnRennie I rarely get good marks

John Rennie

@Akash.B Looking back, I'd say the key thing is to figure out what you enjoy doing then do that.

PM 2Ring

IIRC, one of my grandfathers (who was a builder) taught me the trick with the cork & 2 forks.

John Rennie

In my case I was a stereotypical geek. I used to do maths in my spare time just for fun.

Friends of mine enjoyed doing different things, e.g. sport, and spent all their time doing that.

Akash. B

@JohnRennie just for fun?

John Rennie

5:39 AM

@Akash.B I'm afraid so :-)

Akash. B

It ruins my fun

John Rennie

Most physicists I know are basically the same. They do really hard physics because they enjoy it. But different people enjoy different things. Like I said, you need to work out what you enjoy then spend your spare time doing that.

PM 2Ring

I remember the 1st Moon walk. I was in 5th grade, and normal lessons were suspended while we watched it on a little black & white TV. (We didn't get colour TV in Australia until the mid 1970s.

John Rennie

@PM2Ring I have a vague memory that it was in the middle of the night in the UK and my dad woke me and my brother so we could watch it.

Akash. B

@JohnRennie but i still love physics

PM 2Ring

5:43 AM

@JohnRennie I can relate to that. I still do. :) I taught myself differentiation & simple integration in 3rd form, 2 years before we learnt it in class.

John Rennie

@PM2Ring it's a sad life, but someone has to live it :-)

PM 2Ring

:D

PM 2Ring

5:59 AM

Is this comment reasonable?

even though the "front end" and "back end" of the photon may be very far apart That sounds like you're mixing together the wave description of light with the particle description. When a fundamental quantum entity is detected you should model it as a localised point-like particle. — PM 2Ring 3 hours ago

PM 2Ring

6:38 AM

@PranshuKhandal Here's a short PDF with an example of static maglev that only uses a single contact point to maintain equilibrium. Hamsa.

Captain Bohemian

6:52 AM

@JohnRennie I used to think math and physics are quite different.

@Akash.B I also love physics as soon as I know it, but I don't actually have that strong love with math.

actually even until now, I still think physics and math are not that similar.

I only treat things which only appear in math, probably what those mathematicians call pure math, as math.

math appearing in various disciplines aren't real math.

PM 2Ring

7:16 AM

@CaptainBohemian Yes, they're different, although some people, eg Tegmark & his followers think that the fundamental basis of reality is mathematical. I'm kind of sympathetic to that notion, and I was a firm believer of it in my youth, but these days I think that that Platonic philosophy is confusing the map with the territory.

However, there is an intimate relationship between physics & maths, since physics uses mathematics to model reality. We don't try to describe reality directly. Instead, we create models that hopefully capture a subset of reality. We then explore the implications of the model, and test it to see how well the model correlates with our observations.

So if there are aspects of reality that are intrinsically non-mathematical then modern physics has no way of handling them. But that's a very big "if". ;)

@PranshuKhandal Ok. I've just spent half an hour messing around with a pair of flat disc magnets, a pair of forks, and a wooden clothes-peg to hold everything together. I couldn't achieve stable levitation, and any slight deviation from the central axis quickly forces the upper magnet + forks to move away from the central axis.

My forks are made of a slightly magnetic stainless steel, but I don't feel that had much of an effect. So I think your idea of a bowl shaped upper magnet would have the same instability, even if the centre of mass of the bowl were directly below the lower magnet.

PranshuKhandal

7:38 AM

@PM2Ring thanx for trying that, but i believe using 3 might work better, lol

3 fork

:D

But even if COM is below other magnet, the magntic fields are like top surface of ball

and the situation is like balancing a ball (even with the forks), over other ball

even the COM is below the other ball, its near impossible to balance it

Physics Meta

1

Q: negative rep score when neither question nor my answer were downvoted

My answer to this question- Wood: A Naturally Occurring Composite Material? was green-checked as "accepted", although neither the question nor my answer were upvoted (both show zero). However, my rep tally shows a red -2 for my answer. Can anyone explain why this is so- was a user removed, for...

support

PM 2Ring

8:06 AM

@PranshuKhandal Exactly. The way the magnets pushed each other felt a lot like trying to balance one ball on top of another.

PranshuKhandal

8:19 AM

@PM2Ring the pdf is amazing

PM 2Ring

8:35 AM

@PranshuKhandal It's very nice work, especially considering the author's a high school student.

Captain Bohemian

@PM2Ring actually not all physicists know a lot of math techniques. Some physicists focus on using nonmathematical techniques to understand physics, such as experiment or engineering and don't know the detail of math underlying physics. I think a professor who was my seminar teacher is that way. He always frowned on my lab members giving presentations full of math. He often criticized our math-filled presentations lack phyics.

user8718165

8:55 AM

hello @JohnRennie

John Rennie

@user8718165 hi

user8718165

@JohnRennie Why do warm stainless steel utensils stick to table covers which have a plastic coating on them? I mean it doesn't melt and stick.

Is it because of air pressure difference?

John Rennie

@user8718165 I suspect the top layer of the plastic coating softens under the heat and moulds itself to the surface of the utensil.

user8718165

But that doesn't leave any plastic melt on the utensils after pulling them

John Rennie

@user8718165 obviously I can't know for certain because I can't see your tablecloth. But I would guess the coating isn't melting - it's just softening.

PM 2Ring

9:05 AM

@CaptainBohemian That relates to what I said earlier about confusing the map with the territory. When we say that X must happen because the maths says so, we must bear in mind that the maths is merely a map, and we're confident that it gives correct results because prior observations are consistent with it, and all attempts (so far) to find counter-examples have failed.

OTOH, nature is not obliged to behave according to our mathematical models. It's up to us to construct mathematical models which adequately capture how nature behaves. So in science, the bottom line is what our observations tell us, not what the maths tells us.

user8718165

@JohnRennie Thanks al lot...Got it:-)

John Rennie

Plastics tend not to have a precise melting point like e.g. ice. They have a range of temperatures over which they get softer and softer.

This is called a glass transition.

Glass transition

The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials), from a hard and relatively brittle "glassy" state into a viscous or rubbery state as the temperature is increased. An amorphous solid that exhibits a glass transition is called a glass. The reverse transition, achieved by supercooling a viscous liquid into the glass state, is called vitrification. The glass-transition temperature Tg of a material characterizes the range of temperatures over which this glass transition occurs...

user8718165

@JohnRennie wow didn't know that...also the stainless steel ones stick harder than the melamine ones

John Rennie

I suspect steel has a higher specific heat so it stays hotter for longer.

user8718165

@JohnRennie Thanks a lot...got it:-))

Captain Bohemian

9:10 AM

@PM2Ring you are probably correct, but I am so poor at experiment that I often prefer to believe in math than experiment.

PM 2Ring

@CaptainBohemian It gets tricky though, because our theories strongly influence how we observe natural phenomena. We can easily ignore or misinterpret data that our model isn't equipped to handle. A crude example: medieval inventors interested in heavier-than-air flight often added feathers to their contraptions. Birds fly, and all birds have feathers, therefore flying things need feathers. ;)

Captain Bohemian

for example, when I did the experiment of photoelectric effect, it doesn't reflect what textbooks say; it doesn't demonstrate light is discrete as photons, but I ignored it and believe what textbooks say.

PM 2Ring

It can be disheartening when a demo doesn't behave like the textbook says, and it's easy to accept the authorities when you test stuff that's already been tested thousands of times. It must be exciting, but also a little scary when you do cutting-edge work, and there are no authorities to fall back on.

Captain Bohemian

@PM2Ring I only contend with professors or teachers when I find the math I derive doesn't follow what textbooks say. I don't tend to do that when the experiment I do doesn't follow textbooks say.

PM 2Ring

I never tested the photoelectric effect at school. But we did do Millikan's oil drop experiment to determine the charge on an electron. It was a nice feeling to see the quantization coming out of the data, and to get a value that was consistent with the textbook value.

Captain Bohemian

9:24 AM

@PM2Ring when I was a teaching assistant for Millikan's oil drop experiment, the data my students gave me often differ dramatically from what textboks say.

ChoMedit

In my experience, Milikan's oil drop experiment is terribly hard to get original value..

PM 2Ring

Some people just aren't cut out to do labwork. Wolfgang Pauli was notorious for "causing" stuff to go wrong. See en.wikipedia.org/wiki/Pauli_effect IMHO, it's interesting (but also slightly embarrassing) that a great scientist like Pauli genuinely believed in this psychic effect.

Captain Bohemian

actually the schools I studied didn't treat physics experiments very important. They emphasize physics lectures more.

PM 2Ring

@ChoMedit Our results weren't fantastic, but we definitely did get quantization, and our value was reasonably close, but definitely not 6 sigma standard. :)

Captain Bohemian

they think physics experiments are just to let us get a feeling, and we don't really need to know the detail, so we don't usually know how the instruments work out those experiments.

actually it's difficult for us to know the mechanism underlying those instruments because we don't know electronics.

PM 2Ring

9:33 AM

My last high school teacher was great. And if we wanted to try stuff that went beyond the experiment in the textbook, he encouraged us. Eg, we did an experiment to make a crude vacuum tube diode. He was very pleased when my group decided to turn our diode into a triode.

PranshuKhandal

hey everyone

i have a fidget spinner, and i love rotating it

it is best stable when plane of rotation is perpendicular to direction of gravitational field

otherwise, it applies an awkward force on my hand

but isn't it similar to charges, rotating in magnetic field

when they rotate, magnetic field tries to bring their axis of rotation in parallel to its own direction

ia this similarity significant in any way

as we have seen many similarities in electric, magmetic and gravitational forces

should it be asked on main site??

charge -> electric field and magnetic field

mass -> gravitational firld

*field

PM 2Ring

9:49 AM

Oh oh, newish member xray0 is on an editing spree.

I just left them a comment:

@xray0 Your edits are helpful, but please do them in small batches so you don't flood the front page with old questions. See physics.meta.stackexchange.com/questions/11150/… — PM 2Ring 1 min ago

@PranshuKhandal I think it's similar, but I'd like to see others' opinions.

PranshuKhandal

10:08 AM

Hey @JohnRennie

John Rennie

@PranshuKhandal hi

PranshuKhandal

what do you think about this??

about relation in gravity and Magnetism

i think there are some differences

you can rotate fidget in both directions

but this is not the case with charges

John Rennie

@PranshuKhandal I'll have to get back to you on this. I'm busy at the moment.

Anonymous

In case people didn't notice yet. :P

GodotMisogi

10:20 AM

Damn it, @Blue!

Anonymous

Ninja'd.

Anonymous

:P

John Rennie

Ah, it must have just become April 1st somewhere in the world.

Anonymous

Yesh

GodotMisogi

Why does PSE have virgin sans font while MSE has Chad Comic Sans?

Anonymous

10:29 AM

@GodotMisogi ...

Anonymous

That's a good question...maybe we should as on Meta SE. :P

GodotMisogi

You're too late; I already got a screenshot of the cancerous emо̄ji gif

Anonymous

Screenshot of a gif?

Anonymous

That's no good. You should have gotten hold of the link.

GodotMisogi

I-I'll sue!

Anonymous

10:34 AM

17

Q: How to disable "time travel" entirely?

Every time I open a question I get this oh so funny 90s feel with scrollers and whatnots. In every question I need to click it off. Is this an attempt to keep people from using the site for a few days or how do I tell you "please never ever do anything like this if you want me to keep contributi...

support bug user-interface april-fools time-travel-mode

Anonymous

Gotta love people complaining. :)

Anonymous

@GodotMisogi In case you didn't know, you can still find the link in the message history. ;)

GodotMisogi

@Blue Thanks, I'll see you in court

PM 2Ring

FWIW, the plain mobile view is normal.

Physics Meta

0

Q: Help needed. format turned colored and with bubbles when I hit a question

A nonsense format comes up when I hit on the list of Physics a question to look at it. Colors and bubbles and distracting fuss. Help please. It happened after I rejected and edit by xray0, but it could be a coinidence. ( for many of the corrections I do not see a difference, for some there is gr...

support format

Anonymous

10:46 AM

@PM2Ring It's a bug...they're apparently working on it. The back to the future button should actually disable it on all pages.

Anonymous

Sorry y'all. It's a bug. We're working on a fix. Thanks for reporting it. We'll get this adjusted shortly. — Catija ♦ 2 mins ago

PM 2Ring

@Blue Thanks.

PM 2Ring

11:04 AM

Oh boy. Those people complaining on SE Meta wouldn't have coped on XKCD when Mod Madness was a thing. For about 2 weeks, crazy word filters made life very interesting. ;) A couple of those filters are now permanent. Eg, "tweaking" gets automatically converted to "twerking".

In other news, xray0 seems to have gotten the message. Or has found something else to amuse themself. ;)

ACuriousMind

12:10 PM

I love the little flames around "Hot Network Questions"

Transcript for