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

Homework Help: Uncertanties and errors question

  1. Sep 9, 2010 #1
    *Before I start, I just want to say that this is only my second day in IB Physics. I had never taken Physics at in in high school prior to IB Physics, so I really had to read up and pretty much self-teach myself a bit of it over the summer. Of course, even now I still have absolutely no idea what I'm reading (but neither does anyone else in my class). The answers and explanations to these problems are only based on my meager understanding of Physics.*

    1. The problem statement, all variables and given/known data
    You measure the oscillations of a pendulum four times, and find that it makes 15 complete swings in times of:

    8.13 s, 8.22 s, 8.19 s, and 8.15 s.

    You calculate a standard deviation (read from your calculator) of 0.0403112887416037 s.

    The correct way to report the answer (with the proper number of significant figures!) is to say that the period is: ? seconds

    With an uncertainty of: ? seconds

    *There is little tolerance for error in this specific question*

    2. Relevant equations

    -I entered the variables in my calculator just to see what the average was. I got an average of 8.17 seconds using the sig-fig calculator and the standard deviation was the same.
    (There really aren't any relevant "equations" in this problem)

    3. The attempt at a solution

    -Based on what I learned, you can only express uncertainties in one sig-fig, and that it must match the level of precision. So, based on that I wrote down: 8.17 ± .04 seconds. But, apparently this is wrong. Why? Any help is gratefully appreciated.
    Last edited: Sep 9, 2010
  2. jcsd
  3. Sep 12, 2010 #2
    I'm not sure if there is more to this problem that I don't know about, but this is all of the information I have so far, as I'm still trying to figure this problem out. *Also, I noticed that a pretty lackluster thread titled *help* seemed to be getting more attention when, clearly, the OP didn't read the FAQ. -.-*
  4. Sep 12, 2010 #3


    User Avatar
    Homework Helper

    Is the question asking you to find the actual period? Because the data you show is the time it takes the pendulum to go 15 swings, not one (which is what the period would be).

    Am I misreading what you've written?
  5. Sep 13, 2010 #4
    I copied the problem directly from the website from which it was assigned, so I suppose it is asking me to find the actual period.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook