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

Why use unit vector for this, and not for that?

  1. Feb 11, 2009 #1
    the car problem in my text uses the unit vector, and the second one doesn't...

    how come?


  2. jcsd
  3. Feb 11, 2009 #2


    User Avatar
    Homework Helper

    The second problem is more complex and requires vectors to take care of the 3 directions involved. The first (car) problem has only one direction so no need for vectors.
  4. Feb 11, 2009 #3
    but it did the opposite of just that.

    the car used 'unit' vector....

    while the second does not use the 'unit' vector
  5. Feb 12, 2009 #4
    The first problem is asking for a moment about an axis. I'm pretty sure this is why you have to employ the unit vector in your calculations. If i recall correctly (been awhile since I was in statics) the unit vector here will be j or [0i 1j 0k]. Is that familiar?

    The second problem is asking for a moment about a point.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook