Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Hi! I'm Dashin! And I'm 13!

  1. Mar 26, 2012 #1
    (No, I'm not 13!, I'm 13. I am not THAT old)

    Hi! I'm not sure where to put a "Hello" message, so I suppose here will do. Great to be here.

    Before you think "GTFO 13 year old", I love Complex Numbers (I prefer "Complex" to "Imaginary" because "REAL" numbers are actually figments of our imagination also) and I also love the satisfying answer of e^(pi*i)=-1, and the way it works.

    So, um, yeah. Not sure what else to say here. I'm a bit of a Math Nazi when it comes to rounding, in that I hate to do it. "A Ball Falls to the Ground at accelleration of 10 Newtons per second"... It falls at 9.81 (still roughly), not 10.

    So... Um... Great to be on a forum with smart people for once.

    ~ Dashin

    EDIT: Great, a math Nazi. I'm actually 13.490303762009785, not 13.
    Last edited: Mar 26, 2012
  2. jcsd
  3. Mar 26, 2012 #2
    Given that you didn't provide a unit of measurement, it sort of works if you are 13! in 1/15*seconds. :biggrin:

    Welcome to PF! Incidentally, what's your favourite fish?

    Ahem. Thou shalt keep significant figures in mind, or risk the wrath of the physicists. :wink:

    Heh. You're only *supposed* to think that. Most of us are just insane. Shhh, don't tell anyone.
    Last edited by a moderator: Mar 26, 2012
  4. Mar 26, 2012 #3
    Happy birthday Dashin.
  5. Mar 26, 2012 #4
    *facehoof* I was being rough, and I meant YEARS old. And... *facehoof*



    Uh, Okay.

    I'm ACTUALLY 13.490303762009785
    Last edited by a moderator: Mar 26, 2012
  6. Mar 26, 2012 #5


    User Avatar
    Science Advisor

    Welcome to the forums Dashin.

    I hope you enjoy your time here and I hope you get a lot out of these forums: I like many others here, do on a regular basis: it's a great community :)
  7. Mar 26, 2012 #6
    It seems like a great community - I got asked about fish.
  8. Mar 26, 2012 #7


    User Avatar
    Science Advisor

    Yeah don't worry about that, those guys are nuts ;)

    If you are curious its a weird initiation rite here kind like an induction ceremony into a tribe kinda thing.
  9. Mar 26, 2012 #8
    Good to have you on board, young Sir.

    I see you're from the UK. Did you skip a few grades to A-Level Maths or is your knowledge of complex numbers and kinematics a result of independent study? In any case, kudos to you. :-)
  10. Mar 26, 2012 #9
    Uhm, Okay? Did I answer correctly?
  11. Mar 26, 2012 #10


    User Avatar
    Science Advisor

    Yeah dude you're fine: your not a witch and we won't burn you at the stake ;)
  12. Mar 26, 2012 #11
    Yeaaaah... this is totally to do with Math...
  13. Mar 26, 2012 #12
    *slaps Dashin with a big, fat, codfish*

    http://files.myopera.com/Chyren/files/fishSlap1a.gif [Broken]

    Now you're officially one of us. Welcome to the PF cult. :biggrin:
    Last edited by a moderator: May 5, 2017
  14. Mar 26, 2012 #13


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    Hi, Dashin!
    Rounding numbers are often the most sensible thing to do, bevause keeping "too many" digits falsely imply a higher degree of accuracy to measured numbers than you actually have.

    Suppose you have to measured numbers 3.7 and 4.3. Your measuring tool is not good enough to distinguish between numbers lying between 3.65 and 3.75, and "3.7" is your measured number for the possible INTERVAL of numbers 3.65 to 3.75. We say you know the "number" to two significant digits, in this case.

    Simliarly, "4.3" stands for any number within the interval 4.25 to 4.35, and we know the "true" number to two significant digits as well.

    When you multiply, for example, 3.7*4.3=15.91, you are to round this off to..two significant digits, i.e, give the answer as..16


    Consider the HIGHEST product the two number intervals could produce, i.e 3.75*4.35=16.3125

    The LOWEST number that interval can produce through multiplication is 3.65*4.25=15.5125

    Thus, your "exact" answer, 15.91 gives the FALSE IMPRESSION that your product must lie between 15.905 and 15.915

    Instead, keeping the answer to two significant digits, i.e rounding 15.91 to 16, then you are saying the "true" answer must lie between..15.5 and 16.5, which is absolutely..TRUE!

    THAT is the real importance of rounding, not to introduce a false level of accuracy in your answers for inexactly measured numbers.
    The best thumb rule is:
    You are to round off your answers to the least number of significant digits in the measured numbers you do algebraic operations on.
  15. Mar 26, 2012 #14
    Oh yeah, obviously for measurements xD
  16. Mar 26, 2012 #15


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    And isn't 9.81 a measurement?
    Suppose you have given the mass of an object to one significant digit, say 2kg.
    If you are to estimate the gravitational FORCE acting upon the object, it is meaningless to keep the acceleration due to gravity at 9.81, but round it off to one significant digit, i.e, 10 (ending zeroes are NOT significant digits).

    Thus, the force upon the object will be 20 N, to one significant digit's accuracy, i.e, the EXACT force lying somewhere between 25N and 15N
  17. Mar 26, 2012 #16
    But not for e or [itex]\pi[/itex]?
  18. Mar 26, 2012 #17
    *le shrug*
    Fair enough.

    I will use as many digits as possible for e or Pi. (obviously no more than 40 for Pi - the amount needed for atoms spanning universe)
  19. Mar 26, 2012 #18


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    isn't "e" the exact value of..."e"?
  20. Mar 26, 2012 #19
    The amount of digits you bother to use is what we're talking about here
  21. Mar 26, 2012 #20
    with numbers like pi and e I usually just use the calculator button >.>

    and round later
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook