GooD MorNInG... Yo..

What is special feature of conservative force??? Beside line integral of closed loop is zero or work is independent of path. Like i need explanations, it is always uniform in space or behave similar in all direction etc..

I need physical explanations.

@123 you're gonna need to be more specific. the entire purpose of potential energy takes advantage of that path independence

Hi @SirCumference I want to understand the general behavior of conservative field in space.

@satan29 Lagrangian mechanics is pretty straightforward. Your JEE studies will have left you with all the mathematical tools you need. You just need to find a good book (or online resource).

There are some recommendations there.

This is just your hourly reminder to use \langle and \rangle instead of < and >

is it okay to infringe someone's copyright on this if the holder doesn't find it?

It's never OK to infringe copyright, but copyright normally allows you to use excerpts from works on sites like this.

I recently flagged a post which tempted to infringe the copyright but someone declined it saying SE neither can protect nor enforce copyright infringement

@SrijanSuryansh what was the post? Can you post a link to it?

unfortunately it is deleted now

Ah, yes, I saw that as well and I also flagged it as a copyright violation.

I'm a bit surprised you got a negative response from a moderator.

@JohnRennie and yours got accepted right?

I didn't check.

Ah, I just looked and my flag got rejected as well!

despite the fact you are a moderator

There might be some legal issue that means the SE have advised mods not to take any action on copyright infringement.

@SrijanSuryansh I'm not a moderator!

A lot of people think I'm a moderator because I'm so active on the site, but I'm just a regular user like you.

ohk

The Physics room is a private room (despite the name).

@JohnRennie ok

It was being used to help the room owner with their JEE preparation.

A lot of the chat here is with students seeking help with their JEE studies. I guess you have that to come.

no but yes i do prepare for jee

Are you giving it next year?

2022

OK, a couple of years yet :-)

Hi

you said physics!

@soheil hi :-)

Can you solve my question it is both about math and physics?

Thanks :)

@JohnRennie but i'm just taking it as a backup i want to study Astronomy but IIT is not good for that

@SrijanSuryansh so you'll be applying to an IISER?

Over the years I've helped a lot of JEE students and they've told me about how it works. I don't know a lot about it though.

@JohnRennie So do I

@SrijanSuryansh @SrijanSuryansh There is an aeronautics branch but you might be already aware of that

@AkshatSharma unfortunately it is not of good standards .

@SrijanSuryansh Perhaps, I don't know much about that

That is what I've been told

Ah ok

How to write LateX for arrow cross words with value.

for example i want to show $\cos180\deg$ cross cos angle with value 1.

\times

Is anyone there?

...

@Turbo hey

@NiharKarve hey!

I wanted to ask - a problem has an asteroid of radius 1km illuminated by sunlight. The question asks what area should be used to calculate the solar power absorbed by the asteroid.

The answer is 3.14km^2 but my first thought is 6.2km^2 as it's half the area of the sphere which is 4pir^2

What am I missing?

the "effective" area on which the sunlight falls is just a circle with radius = 1 km

@satan29 why isn't it half a sphere? e.g. when you look at the moon one half is illuminated

that is true, but when we talk about power, it is Intensity * (area normal to the path of light)

not just intensity * area

this will be explained better by a diagram, wait

@Turbo if you think about the area of light that is about to hit the asteroid, it'll be pi r^2. The intensity of light is uniform throughout this area.

@Nihar gotcha!

Thanks :)

No problem :)

@JohnRennie @SrijanSuryansh Moderators are not responsible for policing copyright violations, see e.g. meta.stackexchange.com/a/240769/263383. We act against plagiarism and we want links to articles and books to be to stable sources (arXiv, DOI, see also physics.meta.stackexchange.com/a/4564/50583), but we don't usually do anything just because something infringes copyright

How did the test runs for the mulled wine dispenser go?

:^)

@skullpatrol hold on, give ACM some time to mull it over

it works as designed

@ACuriousMind thanks for informing

@JohnRennie you there?

@satan29 hi

did you get my ping from the physics room?

Sorry I've been busy all morning.

if we sit on a giangatic gyroscope inside a airplane then we will experience zero turbulence right?

@SrijanSuryansh the gyroscope would keep you pointing in a constant direction, i.e. you won't rotate, but you'd still be subject to linear forces if the plane shakes up and down or side to side.

@JohnRennie does orientation of gyroscope decides in which direction it will be pointing constantly?

A gyroscope works because it has an angular momentum due to its rotation, and angular momentum is a vector. The direction of the angular momentum vector can only change if we apply a torque to it.

But when gyroscopes are used in inertial guidance systems in airplanes they are mounted in a device called a gimbal that prevents any torque being applied. Since no torque can be applied the direction of the angular momentum vector cannot change i.e. the spin axis always points in the same direction.

ohk thanks(ʘ ͜ʖ ʘ)

I tried to calculate the distance travelled by the lowermost point in case of pure rolling

are utilised distance travel by the point is equals to distance travelled with respect to centre of mass plus distance of centre of mass

Due to which I got wrong answer is it due to the fact that we cannot write distance this way because it is a scalar

It's not clear at least to me what you've just explained @PrateekMourya

In one revolution the distance travelled buy lower post point with respect to centre of mass is 2 Pi R

The distance travelled by centre of mass is 2 Pi R

Since the combined rotation and translation is superposition of the motion of centre of mass and motion with respect to centre of mass

So I simply added them

Yo....

hello peeps

how do we type gradient in mathjax?

nabla?

yes

AHHH mybad i was just typing \grad

itll be \nabla i guess

yes

$\nabla$

It works

I've wondered why we so desperately want to calculate correlation functions in QFT for a while since it's a seemly quite abstract quantity. But is it simply because they appear in the LSZ reduction formula?

Like, is the LSZ formula an industry standard formula for calculating qft amplitudes?

@Charlie yes

:O

also, in non-hep contexts like condensed matter the correlation functions - as expectation values of polynomials in the fields - often relate to important quantities of the matter system you considering

Ah I see

The a) part of answer and in 1st picture and the explanation in second picture why are they different

I mean in 1st picture it says that level of submergence decreases and in the second it says due to pascals law

This might be a pretty rogue queaiton

But I'm looking at some data from a telescope and it's giving me a had of 1e8?

Which seems super wrong right

@PrateekMourya They are different situations. I presume they are neglecting the slight change in density of the air when the atmospheric pressure changes; which might have a small effect on buoyancy, but unless the density changed significantly, it would probably be completely negligible. Meanwhile in the kerosene case, the density does change significantly. The ice block goes from being in contact with something of very low $\rho$ on top (so $\Delta P$ is small).

When that air gets replaced with kerosene, the density of the fluid surrounding the block is suddenly much different on the top 90%, which changes the force balance and therefore the resting position. If you poured kerosene on top of the water a boat was resting in and it submerged the boat too, the boat would go higher above the water level; but now it's submerged in kerosene.

Lol they assumed constant density of kerosene to solve next part of question

So we assume zero density of air

@PrateekMourya Which is totally fine. The density change due to pressure is generally low for fluids, compared to a gas like air. It's the fact that the low density air surrounding the object was replaced with relatively quite dense kerosene that changed the balance, not any change in the kerosene's density.

Do we assume negligible density of air

@PrateekMourya Yeah. If you do the math with density of air you can see how it doesn't really make a difference.