The h Bar

12:45 AM

@bolbteppa oh lawd

Slereah

6:12 AM

There are plenty of criticism of math textbooks

Some by none other than Feynmann

Emilio Pisanty

7:12 AM

@DanielSank facebook.com/381748875331496/posts/1200900936749615

3

8:28 AM

Feb 20 '15 at 15:17, by ACuriousMind

Lie-to-children

A lie-to-children is a simplified explanation of technical or complex subjects as a teaching method for children and laypeople, first described by science writers Jack Cohen and Ian Stewart. The word "children" should not be taken literally, but as encompassing anyone in the process of learning about a given topic regardless of age. It is itself a simplification of certain concepts in the philosophy of science. Because some topics can be extremely difficult to understand without experience, introducing a full level of complexity to a student or child all at once can be overwhelming. Hence elementary...

vs

18 hours ago, by bolbteppa

Lies My Teacher Told Me

Lies My Teacher Told Me: Everything Your American History Textbook Got Wrong is a 1995 book by James W. Loewen, a sociologist. It critically examines twelve popular American high school history textbooks and concludes that the textbook authors propagate false, Eurocentric and mythologized views of American history. In addition to his critique of the dominant historical themes presented in high school textbooks, Loewen presents themes that he says are ignored by traditional history textbooks. == Themes == In Lies My Teacher Told Me, Loewen criticizes modern American high school history textbooks...

DanielSank

9:41 AM

@EmilioPisanty Haha, thanks. You're the second person to send me that.

10:25 AM

@JohnRennie I have a question!

John Rennie

10:37 AM

@Akash.B hi :-)

11:19 AM

@JohnRennie hi again

I have a doubt regarding newton's law of gravitation and 2nd law of motion

One law says that force experienced by a body is constant while the other is saying that it varies with distance

Which is right?

John Rennie

@Akash.B hi

The second law doesn't say that the force is constant. It just relates the force to the acceleration.

In fact you have to combine the two laws to get the gravitational acceleration.

Emilio Pisanty

@DanielSank well, it does have your name written all over it =)

DanielSank

11:41 AM

Hi, everybody.

hi pal

welcome

12:24 PM

@JohnRennie okay let me say

The force that earth attracts is given as "my"

Srry mg

Right !

Since acceleration due to gravity is a constant can't we say that force is constant as per second law?

Mass is also a constant

yes, continue please

So can't you find something fishy here?

what do you find "fishy"?

When we analyze universal law of gravitation

It says that force varies with distance

But when we take a glance at second law

between which two masses?

12:30 PM

Between earth and an object

Acceleration and mass is constant

So force is constant

@skullpetrol are you understanding? What I meant

not really, but continue your line of reasoning please...

Okay

Let me start from scratch

What is universal law of gravitation?

The force between an object and the earth is directly proportional to the product of their masses and inversely proportional to their distances

Note the point inversely proportional to the distance

Okay now let's get on to the second law

Let me reduce it to it's equation that is $$f=ma$$

Here acceleration due to gravity is constant which is 9.8m/s and so mass is constant

So what does it mean ?

Force is a constant

As per second law

@skullpetrol so got it right now?

not 9.8m/s, but 9.8m/(s^2)

Okay sorry about that

np

may I suggest you read this

the value of g is equivalent to the ratio of (G•M_earth)/(R_earth)^2

12:46 PM

Did you get what I am saying?

JMac

@Akash.B Acceleration is only approximately constant

I think this page will answer your question about the distance @Akash.B

1:03 PM

@skullpetrol well if I throw a ball upwards

The r varies right?

Here r really means the distance between the body and object , right?

how much is that variation compared to the radius of the earth?

1:32 PM

It's not about how small

It's still bound to the fact that force varies

I am looking for an accurate explanation

More Anonymous

1:52 PM

Hey guys for once i want to post an answer

But its an original answer

I have asked a friend to verify it

Would anyone be willing to be a 2nd checkpoint of this derivation?

I've already tried googling it (can't find it) :(

JMac

2:22 PM

@Akash.B The accurate explanation is that the acceleration is only approximately the same for small variations of distance from the centre of the earth. If you do the math, you can see that it really doesn't change much based on height, especially for regular people doing things on Earth's surface. It's not exactly the same, but often the change is so small that it can be ignored.

Anonymous

2:47 PM

@DanielSank Heyo! I noticed you're a co-author on Google's supremacy paper. Could you answer this if you get time? :D

2

woah, you exist!

Anonymous

@danielunderwood Hiii!

Anonymous

Yeah, I've been a bit busy lately...didn't pop in much :P

school/research I suppose?

blue? is that really you :-?

welcome back pal

skillpatrol

2:55 PM

did somebody say blue has returned :P

Anonymous

@danielunderwood Yeah, internship and job placement season :)

Anonymous

Was preparing for the software internships...didn't manage to get one though. So applying to the research internships for now :P

Anonymous

@skullpetrol Hehe, yes. How're you doing? :D

I'll trade you a full software job for a research internship hah

@SanchayanDutta fine thx

2:58 PM

Is this for next summer? Do you guys have the same May-Aug break as we have in the US?

Anonymous

This year's summer was mostly spent on doing some Mathematica calculations on the geometry of entanglement stuff (PPT/NPT bound entangled states)

Anonymous

@danielunderwood Yup, for summer 2020. However, most people who do well in the internships are offered a full-time job. We had folks from Microsoft, Amazon, and Samsung coming in this year and a few of my classmates managed to get internships there. I did relatively badly as I haven't practised competitive programming in a long while. Brushing up on my C++ skills now (STL!!!!) :P

Anonymous

How're you doing? New job or continuing at the previous data science company?

3:18 PM

Oh nice! Though "competitive programming" doesn't sound pleasant to me

Well it's the one that I started in January, but more data engineering and security than data science. I do get the occasional day to do data analysis though, so it's decent!

Q: Can we consider MR Imaging questions as on-topic unless they ask for specific engineering solutions?

@JMac So what if i throw a ball from aeroplane?

Flying at almost 40000 feet

Physics Meta

1

Context: This question on basic principles of image formation in medical MRI was asked in May 2014, received an accepted answer at the time, and was left unchallenged until August 2019, at which point I decided to attempt to summarize in some detail the topic in an answer that was well received. ...

discussion

JMac

3:40 PM

@Akash.B It would be slightly different, but less than 1% change in the acceleration

4:07 PM

@Akash.B 40k feet is about 12 kilometers. there's a lot more atmosphere to go at that point: nasa.gov/mission_pages/sunearth/science/atmosphere-layers2.html

user2723984

4:19 PM

does anybody know what's the deal with the quantum supremacy paper? It seems it was retracted soon after it appeared, now it's possible to find it on the web but not on official sources

I thought the point was that it wasn't officially published yet, just leaked?

user2723984

if I look online I only find sensationalist articles saying that google can now compute the meaning of life or something

@Semiclassical ah, so even the first appearance wasn't official?