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

Time Doubt

  1. Feb 17, 2013 #1
    Hey peple i always have this doubt ^^ the people say the day have 24 hours right? so the day begin at 00:00 a clock for example if the day 1 begin at 00:00 a clock ends 23:59 and 59 secounds right ?? so isnt 24 hours cause lack 1 secound right??? thanks for future answers.
  2. jcsd
  3. Feb 17, 2013 #2
    Hi, darksoda,
    the last second of the day begins at 23:59:59, but the day does not end at the beginning of the last second; it ends at the end of the last second.

    It's like having 10 Lego blocks in a row, and measuring only 9 because you measure from the beginning of the first block to the beginning of the last block.
  4. Feb 17, 2013 #3
    thanks for the answer so lets see if i understand ^^ 0:00 is other day right ? so this one secound is counted before 0:00 ?
  5. Feb 17, 2013 #4
    Its sort of for the same reason that when you go on a vacation you stay for seven days but only for six nights. You are counting by the end point, but as Dodo said the more important thing to count is the duration of the whole second.
  6. Feb 18, 2013 #5
    Well, this is similar to asking how many times in a day does the hour hand point to 12.

    If one meant "in a day" to mean a single instance of a day, then the end points of the day are included and the answer is 3 because it starts at 12, passes 12 at noon, and ends at 12.

    But, if "in a day" was meant to mean over some series of days, then you have to adjust the idea of a day length so as to not count the 12's twice as the ending of one day and the beginning of the next. Each day length interval has one end point included and the other open... with an additional interval end point either at the beginning or end of the series.

    So you set a convention that either says 12 is the beginning of a day, or 12 is the end of a day when two days are contiguous. That gives each day 2 12's but leaves on extra 12 either at the beginning or end of the series of days, depending on which convention you choose.

    So for one day you would have 3 12's (1x2)+1... (stealing the formula from below, but this is not how the calculation would be for the one day instance; but its consistent)
    For two days, 5 12's (2x2)+1
    three days, 7 12's (3x2)+1
    So number of days=N, then number of 12's is (Nx2)+1

    The series trends to 2/day...
    1 day->3/1=3
    2 days->5/2=2.5
    3 day->7/3=2.3333
    100 days-> (201 12's)/100=2.01
    1000 days-> (2001)/1000=2.001
    10,000 days->20,001/10,000=2.0001

    ...where the indefinite length of the series of days allows the number of 12's "per/day" to be general ("2"), for any finite segment of the indefinite series where either convention gives each day one inclusive and one exclusive end point for its length interval.
    But that must be seen similar to a "rate". The number of actual 12's counted in a finite series of days standing apart from the indefinite series must include the additional 12 that is the beginning or end of the finite series, depending on the convention chosen.
  7. Feb 18, 2013 #6
    0:00:00 is the exact frontier between last night and this morning. The numbers are, so to speak, located *between* the span of the whole seconds: the first second begins at 0:00:00 and ends at 0:00:01, the 2nd second goes from 0:00:01 to 0:00:02, and so on.
    Last edited: Feb 18, 2013
  8. Feb 18, 2013 #7
    thanks for all who answer so we really count the final secound ^^
  9. Feb 18, 2013 #8


    User Avatar
    Staff Emeritus
    Science Advisor

    Look at a watch, when the second hand is on 59 it takes 1 second to flick to 00. This is the 60th second.
  10. Feb 19, 2013 #9
    Why wouldn't we? Any time before 00:00:00 counts as the same day, because 00:00:00 is exactly when the next day starts. So, between 11:59:59 and 00:00:00 is one second of time passing in the same day.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook