Problem Solving Strategies

yuvraj singh

5:34 AM

@JohnRennie, morning.

John Rennie

@yuvrajsingh hi :-)

user8718165

Good Morning sir :-) @JohnRennie

John Rennie

@user8718165 hi :-)

user8718165

@JohnRennie Sir, winter bash's on :-) I also need hats :-(

yuvraj singh

I recently posted a question, on space. Stack exchange.

@JohnRennie

0

Q: Space and Newton laws

Actually I am a high school student reading about Newton law, like inertia, momentum, and third law. When I start thinking about space, is Newton law are sufficient to describe, events that happened in space. Can we govern everything in the universe for eg. We drive angular velocity, of an plane...

Is it rightly framed, or any error you find in the question ¿

John Rennie

5:38 AM

I think you need to make it clear whether you mean Newton's laws of mechanics, or Newton's law of gravity.

Newton's laws of mechanics apply when velocities are low in comparison to the speed of light, and for faster speeds we need to use special relativity.

Newton's law of gravity applies for weak to medium gravitational fields, and for stronger gravitational fields we need general relativity.

yuvraj singh

@JohnRennie ah, OK sir.

I will update my question.

Actually sir if u notice, I have written an event in last.

John Rennie

For example do you know about the anomalous precession of Mercury?

Or you might be interested in this question:

105

Q: Could we send a man safely to the Moon in a rocket without knowledge of general relativity?

I'm wondering if it's possible to send a man to the Moon using equations consistent with Newtonian gravity and without the elaborate tools of Einstein gravity. Are the predictions made by Newtonian gravity sufficiently precise to plan a successful voyage? If not, where would the Newtonian equatio...

newtonian-mechanics newtonian-gravity rocket-science moon space-travel

yuvraj singh

Through general relativity right sir.

John Rennie

Yes

yuvraj singh

@JohnRennie i have read something about it.

If I say anything wrong please correct me OK.

This precession rate had been precisely measured using data collected since the 1600's, and it was later found that Newton's theory of gravity predicts a value that differs from the observed value. That difference, which I am calling the anomalous precession, was estimated to be about 43 arcseconds per century in Einstein's time.

I have heard that general relativity predicts an additional correction that is almost exactly sufficient to account for that 43"/century difference

This was the lines which I remember.

John Rennie

5:48 AM

@yuvrajsingh Yes, that's correct.

yuvraj singh

@JohnRennie actually I was reading your answer.

@JohnRennie please go to my question again, they are closing it with a stupid reason.

John Rennie

I'm not sure your question is really on topic for the Space Exploration SE. Unless you were specifically asking about how general relativity needed to be taken into account for planning space missions.

It sounds more the sort of question I'd ask here or on the Astronomy SE.

yuvraj singh

@JohnRennie I have some questions, can you. answer please.

Rest I will delete the question.

John Rennie

Monday mornings are pretty busy for me. I need to start work in about 20 minutes then I'll be working for hours. But if you have a quick question I'll try and answer it.

yuvraj singh

It might get lengthy, once you finishes the work. Ping me.

John Rennie

6:01 AM

OK

yuvraj singh

In morning I was watching this

Queen Elizabeth II Speech: State Opening Of Parliament (1960) | British Pathé

►

@JohnRennie

John Rennie

Yes?

yuvraj singh

OK, is the house Speaker in Britain is queen.

Or king.

John Rennie

There is a role called "The Speaker of the House" but that is an appointed role not the King or Queen.

Speaker of the House of Commons (United Kingdom)

The Speaker of the House of Commons is the chief officer and highest authority of the House of Commons, the lower house and primary chamber of the Parliament of the United Kingdom. The current Speaker, Sir Lindsay Hoyle, was elected Speaker on 4 November 2019, following the resignation of John Bercow. The Speaker presides over the House's debates, determining which members may speak and which amendments are selected for consideration. The Speaker is also responsible for maintaining order during debate, and may punish members who break the rules of the House. Unlike presiding officers of legislatures...

M. Guru Vishnu

@JohnRennie, Hi sir. May I ask a quick doubt from Polarization?

John Rennie

6:09 AM

@M.GuruVishnu Yes

M. Guru Vishnu

@JohnRennie, Sir, when a light ray is incident at Brewster's angle, how would you explain that the reflected ray is polarized completely but the refracted ray isn't in an intuitive manner? (I read a question on PSE which wasn't useful to me)

John Rennie

I'm not sure there is an intuitive way to explain this.

The reflection and transmission coefficients are calculated by requiring that the electric and magnetic field of the light be continuous across the interface. In principle this is a simple requirement, but in practice it gets very complicated.

M. Guru Vishnu

@JohnRennie By intuitive way, I meant by not using Fresnel equations (which I don't know) sir.

John Rennie

You end up with the Fresnel equations and these are pretty complicated.

@M.GuruVishnu that's the problem, I don't think there is an intuitive explanation. Or at least I don't know of one.

M. Guru Vishnu

Ok sir. I'll just accept them as a fact and proceed. Thank you for your time :-)

yuvraj singh

6:33 AM

@JohnRennie morning hi, Alesha here.

Can you answer my quick question.

John Rennie

@yuvrajsingh hi. I'm working now I'm afraid. I'm going to be working for several hours. Monday mornings are very busy for me.

yuvraj singh

It is a short one.

I promise it will not take much time. @JohnRennie

John Rennie

@yuvrajsingh Go on then :-)

yuvraj singh

Actually, I have difficulty in understanding one easy question, question says a man can, t see distinctly object at distance more than 60cm.the power of the lens will be.

Now my query is. @JohnRennie

There tow cases when men can, t see the object either light rays converge before the retina or light rays converge beyond the retina.

So how do I identify which cases is applying here.

John Rennie

The implication is that the man can see things well when they are closer than 60cm but not when they are farther away than 60cm.

yuvraj singh

6:40 AM

Yes.

John Rennie

So at infinity the rays are converging before the retina, then as the object gets closer the image distance $v$ increases until it matches the distance to the retina at $u = 60cm$.

yuvraj singh

OK,

So, what about power then

John Rennie

Well the power is just $1/f$ isn't it?

So you calculate $f$ from the info you're given and from that calculate the power.

Oh wait. You mean you're being asked the power of the lens needed to correct the man's eyesight?

yuvraj singh

Yes.

John Rennie

@yuvrajsingh The total focal length of the lens in the man's eye and the correcting lens needs to be equal to the length of the man's eye, i.e. the distance to the retina. Yes?

That way he gets a perfectly focused image when the object is at infinity.

yuvraj singh

6:49 AM

So 1/f=1/v

That is equal to retina distance.

John Rennie

Let's call the retinal distance $\ell$, then the total focal length has to be $\ell$ so the total power has to be $1/\ell$.

yuvraj singh

OK.

John Rennie

The power of the lens in the eye is $1/f_{eye}$ and the power of the correcting lens is $1/f_{lens}$, and powers add. So we end up with:

$$ \frac{1}{\ell} = \frac{1}{f_{eye}} + \frac {1}{f_{lens}} $$

And you can calculate $f_{eye}$ from the fact the man can see a clear image at $u = 60cm$.

yuvraj singh

So what I take for v, for the eye lens. @JohnRennie

John Rennie

@yuvrajsingh you known that when $u = 60cm$ the image distance $v = \ell$. Yes?

Because at 60cm the man can see the image clearly.

@yuvrajsingh Yes?

yuvraj singh

7:00 AM

OK.

John Rennie

So:

$$ \frac{1}{f_{eye}} = \frac{1}{60} + \frac{1}{\ell} $$

And you can use this to substitute for $1/\ell$ in the first equation.

yuvraj singh

But still l is unknown here.

@JohnRennie

Sorry sorry, my mistake. Tha KS sir.

I have wastes your time.

John Rennie

:-)

yuvraj singh

10:19 AM

@JohnRennie. Hi.

John Rennie

@yuvrajsingh hi :-)

yuvraj singh

Are you free now.

@JohnRennie

John Rennie

10:36 AM

@yuvrajsingh I'm doing bits and pieces of work, but I can chat as well :-)

user8718165

3:56 PM

hello sir @JohnRennie Is your lunch finished sir?

John Rennie

@user8718165 yes. If you want to ask anything I'm free.

skillpatrol

And freedom tastes of reality?

John Rennie

@skillpatrol reality is over-rated. I avoid it if at all possible.

skillpatrol

:D

yuvraj singh

4:15 PM

@JohnRennie, hi.

John Rennie

@yuvrajsingh hi

yuvraj singh

Sir, can I ask your typing speed per minute.

John Rennie

I'm a really slow typist.

yuvraj singh

I am too.

There are some INSTIUTE which provide typing course.

John Rennie

I never learned to touch type, and now I'm getting old my fingers are starting to stiffen up so I'm even slower :-)

yuvraj singh

4:17 PM

Ah,.

John Rennie

@yuvrajsingh actually I wish I had learned to touch type. If you have the opportunity to go on a touch typing course I would take it.

yuvraj singh

Actually I am learning it online.

John Rennie

Pretty much all the programmers I know who have taken touch typing courses have found it very useful.

3

@yuvrajsingh if the online course is good then go for it

yuvraj singh

Yes.

He is a very good teacher, which genuine method.

John Rennie

@user8718165 you found a hat typo! :-)

yuvraj singh

4:19 PM

But he said we have to practice every session 7 times.

John Rennie

@yuvrajsingh see how it goes I guess.

user8718165

@JohnRennie Yeah sir.... :-)

yuvraj singh

Actually today lecture he said.

John Rennie

If you can do fewer repetitions and still type fast then go for it.

yuvraj singh

To put our figures on second row. Asdf leave gh. For second and fingers.

John Rennie

4:21 PM

@user8718165 I suspect your post will be closed because it's not really a physics SE related post. It should probably have been on the mother meta.

yuvraj singh

@JohnRennie problem is that, I am using laptop, so I am not sure whether it really help to increase speed.

John Rennie

@yuvrajsingh how are you finding it? Are you finding his advice works?

user8718165

@JohnRennie okay sir...Can I post there?

yuvraj singh

@JohnRennie, yes, his first advice was to type correct, rather increasing speed.

John Rennie

@user8718165 yes, if no-one else has posted about it already.

@yuvrajsingh that makes sense I guess.

I don't really know because I'm such a bad typist! :-)

yuvraj singh

4:25 PM

Let see, today I completed 45min, typing first lecture homework.

skillpatrol

why not relearn now sir?

John Rennie

@skillpatrol I don't care about it enough to put the effort in :-)

skillpatrol

ok

yuvraj singh

@JohnRennie can you make me room owner.

John Rennie

@yuvrajsingh have you found it made your typing better?

@yuvrajsingh yes, let me see if I can figure out how to do that ...

yuvraj singh

4:27 PM

Actually today it was first day., so actually I missed the process but yes it works.

user8718165

@JohnRennie sir I also want a hat :(

Feeds

John Rennie has added yuvraj singh to the list of this room's owners.

skillpatrol

congrats @yuvrajsingh^

John Rennie

@user8718165 You have to work for the hats! :-)

yuvraj singh

So gentle, the room is discussion for pure physics. It is better to discuss non physics related talk on Chitt chat and stuff

Feeds

4:31 PM

John Rennie has added user8718165 to the list of this room's owners.

John Rennie

I can see this going horribly wrong :-)

user8718165

@JohnRennie thanks for the Christmas Gift sir :-)

skillpatrol

@yuvrajsingh speed typing comes much, much later... after a lot of practicing the accurate typing style

11 mins ago, by yuvraj singh

@JohnRennie, yes, his first advice was to type correct, rather increasing speed.

user8718165

@sammygerbil Hello :-)

user8718165

4:52 PM

@JohnRennie sir, when your avatar is small (one-line messages) you look like a pirate XD

John Rennie

@user8718165 :-)

jeea

7:08 PM

Hello
I am trying to develop a 2d physics simulator, like gravity and other mechanics stuff. If anyone can guide me whether to write my own engine or use already available engine like box2d

If anyone has such knowledge then please help me!

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Problem Solving Strategies