1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Valid Units of Measure for Trig Argument

  1. Sep 20, 2006 #1
    Quick question. If i pass into a trig function something like cos(3pi*15 seconds), do I drop the seconds from the resultant answer since it's not a valid unit of measure for theta?
     
  2. jcsd
  3. Sep 20, 2006 #2
    that's right.
    the inside of the bracket for any trig identity has units of rad (or degrees if you think that way)
    it's common convention to just drop the units though, since rads aren't really a 'unit'.
     
  4. Sep 20, 2006 #3

    jtbell

    User Avatar

    Staff: Mentor

    The argument (the thing in brackets) of any trig function has to be an angle. Seconds are not valid units for angles. If in your example, the [itex]3 \pi[/itex] has units of radians/second, then the units would work out properly.
     
  5. Sep 20, 2006 #4

    Integral

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    If your problem is well expressed you will find that the factor (in your case) of 3 [itex] \pi [/itex] has units of 1/s . Thus you do not drop the seconds, they cancel out.
     
  6. Sep 21, 2006 #5
    Are radians when used in this way normally expressed per second?
     
  7. Sep 21, 2006 #6

    jtbell

    User Avatar

    Staff: Mentor

    Radians per second are the units of angular speed ([itex]\omega[/itex]), which is a very common quantity in problems dealing with rotational motion, simple harmonic motion, and waves.

    Some people prefer not to name the radians explicitly when doing units-analysis because they're not "really" units in the same sense as meters, seconds, etc. Recall that the radian is defined as the (unitless) ratio of two distances: the length along an arc of a circle divided by the radius of the circle.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Valid Units of Measure for Trig Argument
  1. Unit circle and trig (Replies: 10)

  2. Measuring units (Replies: 2)

Loading...