How is your shoulder recovery coming along @JohnRennie sir?

@user85795 hi :-)

I'm fine now, thanks :-)

Glad to hear it!

:-)

Hi All...

Hello @JohnRennie Sir..

I have a question about force. According to newton's second law $F = ma$ , we already setup standard and devices for measuring distance and time so that we can calculate acceleration using these.

But there are two unknown terms remain to calculate if we take standard measurement of force we can calculate mass and vice versa. In this what is standard Force or Mass?

@123 What do you mean by standard measurement?

@VincentThacker We know 1 meter distance and 1 second time. How do we know/measure 1 Newton force?

1 Newton is by definition the constant force you need to accelerate 1 kilogram of mass with a constant acceleration of $1\frac{\mathrm{m}}{\mathrm{s}^2}$

note that Newton, meter, etc. are called units and not "standard measurements"

Hello @ACuriousMind . It means we take 1Kg mass as standard in F = ma, How we calculate 1Kg mass before using this.

@123 The units are defined using SI base units

You can check them out at en.wikipedia.org/wiki/SI_base_unit

Time and length are SI base units

Hello @ACuriousMind . It means we take 1Kg mass as standard in F = ma, How we calculate 1Kg mass before using this.

@123 See en.wikipedia.org/wiki/International_System_of_Units#Base_units

defining units properly is the field of metrology

@ACuriousMind Ookay. I have read KnK book. In this they used 1N force as standard measurement for calculating 1kg mass.

I don't know what "standard measurement" means

again, the name for things like the Newton or the meter is unit

My mistake to use wrong words. I meant to say that defining 1N force

@123 Nope. Force comes from mass. Not the other way around

kg is more fundamental than newton

@VincentThacker That's satisfactory answer thanks a lot. Why plank's constant taken to measure mass?

because it's convenient for high-precision measurements

an older definition was to just say "N atoms of this substance are 1 kg"

@ACuriousMind Plank's constant is just number/constant.I think there is nothing to do with physical quantity.

but getting exactly N atoms of a 100% pure substance is rather difficult, while measuring Planck's constant is much easier

Look at the meter and the second. If you can accept defining the meter via the speed of light and the second, then you must also accept defining the kilogram via Planck's constant, it's the same principle

@ACuriousMind Ooooo. I see. Thanks...

Emilio has an excellent answer here discussing the recent changes to these definitions

@ACuriousMind Thanks a lot. I read this thread.

What is purpose of using constant k in newton's second law... F = k.ma

can someone provide a counter example?

and why value of k = 1 is taken?

or a general loop proof? I don't get how to approach ?

@123 if you want the option of having a constant there, you first need to provide a definition of "force" other than $F=ma$

@ACuriousMind I don't understand. Pls explain. This constant is used in book where they define $F \proportional a$

you need to define $A$ and $B$ separately before you can talk about $A$ being proportional to $B$

In most circumstances, I would view $F = ma$ as the definition of force

it makes no sense to talk about perhaps writing $F= kma$ with some unknown $k$ - unless you have a different definition for $F$, you're free to choose $k$ and this just changes your definition of $F$

I am confused because book used "F" proportional "a" then they written F = k.ma the value of k = 1 is considered why?

how did this book define force, then?

I don't have book right now but i can share you after some hour. Where they define F = k.ma

@ACuriousMind Force is defined to be proportional to mass

that's not a definition

definitions have equal signs in them, for one

just saying "X is proportional to Y" doesn't define X

I am calling my friend to share the book page.

@ACuriousMind They define $a \propto F$ and $a \propto \frac{1}{m}$ then

$a \propto \frac{F}{m}$ and $a = K. \frac{F}{m}$

@ACuriousMind 1drv.ms/u/s!AozWlUoG8z4tnhhxcYoyRMwUyQLm?e=a8mBSm Page-1 of book topic

1drv.ms/u/s!AozWlUoG8z4tnhlvSxc0AUfV7tYC?e=1OLxet Page-2

Your book is confused, Newton's first law is not a "definition of force".

joshphysics' answer here does a good job of explaining the definition of force in the context of Newton's laws

It is govt. text book here for 10th standard students.

that doesn't mean it's good :P

I have read mechanics books but i don't understand. They claimed newton's first law said inertial frame exist. How newton's law tell us that?

as joshphysics says, the presentation of Newton's laws in many cases is not very careful or detailed

To explain how one should think about Newton's laws, I can't do better than his answer, really

@ACuriousMind I have read his answer one week earlier but now after your sharing i am reading it very carefully. Thanks

I have also read in book by Robert Hanlon they said newton's law is not give us the definition of force it gives us effect of force as things are happening in cause-effect.

@ACuriousMind If bus is moving with constant acceleration rightward we feel force leftward to change our state. But why in free fall we won't feel upward when falling downward???

@123 see physics.stackexchange.com/q/196136/50583

@ACuriousMind Thanks I read

@ACuriousMind N atoms of a substance will also weigh differently based on their disposition

Hi everyone. What does a red highlighted post mean? These red highlights disappear when I open PSE in incognito mode.(I'm using Edge)

It looks like a visual thing to make the separation between posts clearer

since only every other post is highlighted

@Charlie there isn't a pattern

Maybe it highlights links that you have/haven't clicked on? Otherwise I have no suggestions left

no

and these appear only on PSE

I...don't see anything red in these pictures

I'm somewhat colorblind, can you describe in a bit more detail what you mean?

There's a very light red shade on some posts

That colour is definitely not red, it's closer to yellow

I mean...the yellow highlight is for posts that are tagged with at least one of your "watched" tags

oh i see

I've never heard anyone describe that color as red

thanks

:-)

my bad

(and of course it disappears in incognito mode because there you're not logged in and hence have no watched tags)

yeah

@ACuriousMind yeah it's yellow

0-6-26-2 in CMYK apparently

now I wonder, @EVO - are you colorblind, do you have really bad color settings on your display, or has your native language different color descriptions from English and 'red' was a guess for the translation of what you really wanted to say?

or some combination thereof...

@ACuriousMind they could also have some night mode/blue light filter on, that could make white look yellow and yellow more reddish

(that arguably falls into "bad color settings")

@fqq I do find it really fascinating that we all take colors as "obvious" but there's really nothing except convention that determines what colors count as "different"

> This article is written like a personal reflection, personal essay, or argumentative essay that states a Wikipedia editor's personal feelings or presents an original argument about a topic. (September 2011)

@ACuriousMind AFAIK I'm not color blind. But I don't think it's yellow, it's more like a light red shade

My brother agreed with me

I too think there is some red in it, but I always thought of it as yellow. Maybe some sort of combination.

this is actually so weird

theres no way that shade can be called red..or maybe I am color blind

Could be my display....?

@EVO probably,yes

Hm, interesting

mmm closer to yellow

Check these colors on your screen

where?

Click the linked word "these"

you linked the "Berlin and Kay" section of the Wiki article from fqq

Put there was'nr any images

*BUt

*wasn't

Scroll down please

There isn't any image

@EVO I think they are referring to the "List of colors in various languages" which you can expand

Yes^

aah thx

np

They are fine. I think it was that light shade of Yellow + Red that made the confusion. I believe it's my display's colour gamut.

suppose i have a bunch of images on my desktop. How do I add them as links in a question? (no pictures, just the links)

@satan29 you can use the image upload as normal and then just change the embedding to a normal link

whether an image link is embedded or a normal link is just different markdown

@ACuriousMind how do I change it to a normal link?

For those curious about their colour vision, try the free X-Rite Color Challenge and Hue Test. It only takes a few minutes. If you're using a blue light filter, turn it off before you do the test.

@satan29 Just use the normal Markdown link syntax [Link description](URL)

@PM2Ring thanks, I got it

What came first p(a/b)=n(a intersection b)/n(b) or p(a/b)=p(a intersection b)/p(b)

@PM2Ring Nice. Score: 2 - should be pretty good(?) also considering that the screen I'm on right now is not the best

I got 0 which is supposed to be "perfect". Still looks kind of red-ish to me though.