The h Bar

1:43 AM

Hi!
@AaronStevens @Gert @KyleKanos @stafusa why are you put [on hold] to my question?
https://physics.stackexchange.com/questions/512877/object-motion-in-air-with-air-resistance
It is actually not "Homework-like questions and check-my-work questions". Did I try to solve it myself? Yes. My solution was defective, so I don't deny that. Actually, I have a big task. It is not Homework or whatever, it is something like "small research work". And asking this question is just a small step to do it. Nobody wants to help me, but one person can.

More Anonymous

@ACuriousMind Would you be okay telling me about "seems to conflate statistical probabilities with inherently quantum probabilities"? I mean we do have $\langle U \rangle = \sum_i p_i U_i $. I know the "all micro-states are equally probable is being challenged" but I'd like to believe that temperature can still be defined even if this is not being measured

Physics Meta

2:04 AM

3

Q: Can we do better at reducing bike-shedding?

"Bike-shedding" is a phenomenon where there is excessive discussion of a topic because it seems easy, so everyone feels that they are competent to discuss it. We seem to have a couple of recent examples: How do I experimentally measure the surface area of a rock? Are we really moving at the spe...

discussion

schn

2:39 AM

How come $mv \cdot \Delta v = \Delta (mv^2/2)$?

John Rennie

6:17 AM

@schn that isn't true, but the infinitesimal form of it is true. We can see this using the chain rule:

Abhas Kumar Sinha

@PM2Ring @Secret Hello! :) Are you safe there? I heard a lot of wildfires there?

Powercuts, food everything okay?

John Rennie

$$ d(v^2) = \frac{d(v^2)}{dv} dv = 2v dv $$

Abhas Kumar Sinha

@schn Agree with @JohnRennie You meant probably infinitesimals like $dv$ rather than $\Delta v$ or you may approximate it, for very small values...

Slereah

9:24 AM

@JohnRennie Heresy!

John Rennie

Hey, when did I claim to be a mathematician? :-)

Every physicist knows that derivatives are fractions really, and those mathematicians are just being spoilsports.

The Monk

10:07 AM

972

Q: Is $\frac{\textrm{d}y}{\textrm{d}x}$ not a ratio?

In the book Thomas's Calculus (11th edition) it is mentioned (Section 3.8 pg 225) that the derivative $\frac{\textrm{d}y}{\textrm{d}x}$ is not a ratio. Couldn't it be interpreted as a ratio, because according to the formula $\textrm{d}y = f'(x)\textrm{d}x$ we are able to plug in values for $\text...

calculus analysis math-history nonstandard-analysis

:D

Secret

11:18 AM

@AbhasKumarSinha We are safe, the fire are far away from our place

John Rennie

11:32 AM

Ironically we have torrential rain and flooding in the UK.

Avnish Kabaj

11:43 AM

103

Q: How do I experimentally measure the surface area of a rock?

I hope this is the right place to ask this question. Suppose I found a small irregular shaped rock, and I wish to find the surface area of the rock experimentally. Unlike for volume, where I can simply use Archimedes principle, I cannot think of a way to find the surface area. I would prefer an ...

measurements

I thought that there would a standardised way to do this

*z

Abhas Kumar Sinha

@Secret well, glad to hear... What about @PM2Ring ? He probably lives near Sydney. Fires are approaching there. National Emergency was also declared there.

Avnish Kabaj

2:19 PM

A scheduled chat meeting is about to begin

How do I figure out that I like research or not

Slereah

2:33 PM

@AvnishKabaj How do you feel about reading papers and working out differential equations

Avnish Kabaj

3:29 PM

@Slereah blehhh

Novalium Company

3:43 PM

,,, ,, ,, ,,,,,

im joking sory

plz no mute

Abhas Kumar Sinha

@NovaliumCompany hey sup buddy?

@Secret any idea of @PM2Ring ? he has not been here for hours...

@NovaliumCompany klol, I was about to do the same

@Slereah How to read complex papers? I've tried reading few, but they way too far and complex for my level... :(

John Rennie

4:02 PM

@AvnishKabaj Seriously?

Avnish Kabaj

4:20 PM

@JohnRennie Yes

John Rennie

@AvnishKabaj you have to want to do it more thn you want to do anything else.

Avnish Kabaj

Hmm

That's the tricky bit

John Rennie

A PhD is years (how many years depends on the country) of having no money but doing something that you find intensely intresting.

If you don't find it intensely interesting it's just years of having no money :-)

Avnish Kabaj

Brrr

Secret

a PhD with scholarship is years with a lot of money and interesting things

(provided you skip lunch that is)

tpg2114

4:22 PM

@Secret Define "a lot" -- it's more than no money, but it's way way way less that you would make with a job

Avnish Kabaj

I never really thought what I wanted to do with my life before jee

Secret

ah fair

tpg2114

It's pretty well known that a PhD doesn't make much financial sense. The opportunity cost is high, and salary growth is (usually) more limited unless you want to leave hands-on research to make more

Abhas Kumar Sinha

@JohnRennie I've seen even 6 years for the people completing PhD and as early as 3 and half years

tpg2114

All the more reason that you have to really enjoy doing it

Avnish Kabaj

4:25 PM

How do you find that passion

Like everyone's like

Abhas Kumar Sinha

:52524190 very less for survival....

Avnish Kabaj

You just gotta follow your passion

Secret

indeed

Abhas Kumar Sinha

@AvnishKabaj become an entrepreneur

Avnish Kabaj

You'll know what you want to do

But I doooooooont

tpg2114

4:26 PM

@AvnishKabaj Try it and see -- use opportunities in undergrad to work in a research lab.

Abhas Kumar Sinha

Entrepreneur [ the Self Made ] Epic Motivational Speech

►

@tpg2114 very less payment...

Secret

Also PM2Ring does not get on alot, but then I may be wrong since I have not been quite active in SE in general

tpg2114

@AbhasKumarSinha It's not about the money -- if it was only about money, then somebody shouldn't be thinking about getting a PhD

Secret

You know what I want: I want to abolish this whole concept of money completely

it is so obstructive

Avnish Kabaj

@tpg2114 will have to grab a senior

Abhas Kumar Sinha

4:27 PM

@tpg2114 completely agree

Avnish Kabaj

@Secret lenin opens one eye

Abhas Kumar Sinha

@Secret agree.

tpg2114

@AvnishKabaj It's well worth it to put in the effort as an undergrad before committing to graduate school. Research isn't for everybody, and the grind of grad school isn't for everybody either. Working a semester or two in a lab will give you the chance to see what it's like (both the work and the culture)

Abhas Kumar Sinha

@AvnishKabaj which collage/branch?

Avnish Kabaj

@tpg2114 as per my knowledge they don't let it students work in a lab over here but you can approach a prof with a 'project'

Abhas Kumar Sinha

4:31 PM

@AvnishKabaj ah okay... a lot of scope..

John Rennie

@AvnishKabaj have you ever found yourself putting in a lot of effort to learn something, not because you needed to learning it but just because you were fascinated by it? It could be anything. Science, or programming, or building model railways.

Avnish Kabaj

@JohnRennie Organic Chem in 11th

Chem stack

Abhas Kumar Sinha

@JohnRennie this is actually a good question... This was needed...

@AvnishKabaj bhai tab samjho ho gya....

Avnish Kabaj

I just devoured clayden

John Rennie

@AvnishKabaj well that's exactly the personality trait you need to do a PhD. There is no logical reason for doing one - the only reason is that you want to.

Maybe you'd be interested in doing a PhD in organic chemistry.

Avnish Kabaj

4:34 PM

Luckily I do have chem in my branch

Let's see

Thanks

Jiminion

When I was in school, Phds seemed to be about doing what the professor wanted to get done, not anything of one's own volition. I guess the trick is finding a topic that both you and your supervisor are excited about.

Semiclassical

the other thing to bear in mind about a phd is that there's a matter of supply and demand involved: there's more places producing PhDs than there are tenure-track positions

Novalium Company

@AbhasKumarSinha why do u keep posting this?

Abhas Kumar Sinha

@NovaliumCompany when I posted before? ;)

Semiclassical

so don't assume that getting a phd automatically means you'll be able to stay in academia

Abhas Kumar Sinha

4:47 PM

@Semiclassical you are a phd?

Semiclassical

yeah

Abhas Kumar Sinha

@Semiclassical background, area?

Semiclassical

condensed matter theory

mostly stat mech / quantum problems

Abhas Kumar Sinha

@Semiclassical quantum computing?

Semiclassical

not yet

though it'd be interesting to go down that route

Abhas Kumar Sinha

4:49 PM

@Semiclassical ah okay...

@Semiclassical everyone is

well, how to become a perfect theoretical physicist?

like landau and lifshitz....

Semiclassical

shrug

Abhas Kumar Sinha

shrug

Physics Meta

5:04 PM

0

Q: Do Physics Hot Network Questions help or harm the site?

There has been some small discussion in the comments of a recent post about Physics SE questions appearing in the list of Hot Network Questions (HNQ). It was also brought up that Physics SE can choose to be removed from this list, but even if this is not a choice to be made, I think a discussion ...

discussion feature-request

Abhas Kumar Sinha

5:25 PM

@NovaliumCompany ah okay... Good Night. I've to go to my dreams to save the world! :)

Novalium Company

@AbhasKumarSinha cool. from what?

Abhas Kumar Sinha

@NovaliumCompany zombies, aliens, vampires and dinosaurs

Novalium Company

@AbhasKumarSinha u might wanna throw AI there, as most likely to happen

Abhas Kumar Sinha

@NovaliumCompany hehehe... Let's not trouble people more here... .. .

Novalium Company

I agree... ... .

Abhas Kumar Sinha

5:29 PM

@NovaliumCompany okay, bye.. ... ...

ACuriousMind

@Slereah Derivatives may not be fractions, but that equation is perfectly valid in terms of differential forms nonetheless!

You don't have to throw the baby out with the bathwater here

Semiclassical

if nothing else, it's a perfectly good shorthand for what you'd do if you did a $u=v^2$ substitution in $\int du$

yuvraj singh

@JohnRennie hi.

John Rennie

@yuvrajsingh hi :-)

yuvraj singh

How you doing. @JohnRennie

John Rennie

5:40 PM

@yuvrajsingh it's cold, windy and raining in the UK right now :-)

ACuriousMind

So, normal day then?

John Rennie

But tomorrow is forecast to be sunny so I'll go for a cycle ride in the sunshine tomorrow and that will cheer me up :-)

@ACuriousMind that's winter in the UK for you :-)

I don't mind it being cold, I don't mind it being windy and I don't mind it being wet. But all three together I'm not so keen on :-)

Actually I'm about to slump into my armchair with a drink and a book I'm really enjoying, so life isn't too bad right now.

JMac

It's been snowing here overnight and all day so far (besides like 30 minutes of rain since lunch). First real snow of the year and it seems like we might get over 20 cm today. Sliding around the streets is always fun.

John Rennie

@JMac in the US? Or Canada?

JMac

@JohnRennie Canada.

John Rennie

5:46 PM

Ah yes, you guys get serious snow. Chester gets a few inches of snow once or twice a year.

JMac

I'm living a bit further north and away from the coast than my home province (for work), so I'm not really used to this much snow this early either. Apparently it's still 14°C back home for me.

John Rennie

Anyhow, my armchair calls. I'll see everyone tomorrow.

JMac

Enjoy your relaxation.

Novalium Company

Russia gets 5 feet of snow everyday and they're all like drinking vodka

Avnish Kabaj

6:25 PM

@NovaliumCompany does modern Russia not get electricity

Aaron Stevens

6:59 PM

@JMac Had a minor dusting here last night and many schools either delayed opening or completely closed for the day. Southern US wimps

Aaron Stevens

7:18 PM

@Malavika Hello

@Malavika Yes, I do

@Malavika As I said before, inertia is technically just mass.

@Malavika No. It is mass.

@Malavika I am not sure what that has to do with inertia. Inertia is not a force, at least not in the sense of Newtonian physics

@Malavika You can argue that certain systems exhibit "inertia" in that they resist change of some kind. I think that is colloquially fine.

But in terms of physics, inertia is just mass.

@Malavika You don't need to. They are the same thing.

Yes. Tell me what the difference is between the two statements I will give below

An object with more inertia will "resist" a force more

An object with more mass will "resist" a force more

"Inertia" is the property of objects to "resist changes in motion"

That is exactly what mass is

More mass, more "resistance"

If you want to be really technical, I suppose one could argue that inertia is a property of having mass.

But I think that makes inertia not really definable then

I think it is sufficient to just talk about mass

Inertia is a concept that I always try to avoid if possible. For this reason here. It confuses people

Just use mass

@Malavika At that point I think it is just semantics.

But inertia is definitely not a force like gravity, electric force, etc.

ACuriousMind

7:49 PM

@AaronStevens In certain contexts, it is useful to distinguish between inertial and gravitational mass, i.e. "that which resists motion" and "the charge of gravity".

If you use just "mass" for the former, you need a different word for the latter

Aaron Stevens

@ACuriousMind That is a good point, although is there actually any distinction?

ACuriousMind

@AaronStevens Well, not in our universe ;)

Aaron Stevens

Cannot mass be "that which resists motion" and "the charge of gravity"

@Malavika Which universe do you currently reside in?

I am fine with saying inertia is a property of mass though

ACuriousMind

@AaronStevens It is essentially the content of the equivalence principle in general relativity that this is indeed the case - mass is both. But in a pre-GR (e.g. Newtonian) understanding of physics, there is no reason for this at all!

Aaron Stevens

@ACuriousMind Yes, that is correct

ACuriousMind

7:53 PM

So in order to appreciate GR's contribution to the resolution of this "mystery", one would need to first introduce the concepts as distinct.

I'm not saying that one should insist on this distinction in other contexts, though

Aaron Stevens

Yes, I agree with all of that.

@Malavika I am not sure I am following what you are saying

@Malavika I think you would have to know what friction is before you imagine a world without friction

Imagine a world without brangafiddles

If you don't know what a brangafiddle is, then you will have a hard time imagining what a world without them would look like

@Malavika it's fine to think of a world without inertia. But if you don't know what inertia is then you don't know what to exclude from this new world

All you can learn from that thought experiment is what arises from that property. But you can't learn what the property itself is from that thought experiment.

@Malavika oh ok. Yeah I suppose if someone else tells you what that world would look like then it gives you an idea of the concept. So it's a good explanatory tool rather than an exploratory tool