1. Limited time only! Sign up for a free 30min personal 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!

Find the curvature?

  1. Jan 17, 2015 #1
    1. The problem statement, all variables and given/known data
    Find the curvature of r(t)=2ti+2tj+k.

    2. Relevant equations
    None.

    3. The attempt at a solution
    The answer is 0 in the book.
    I know the formula for curvature is k(t)=abs(r'(t)xr"(t))/abs(r'(t))^3. I know that r'(t)=2i+2j and r"(t)=0, so r'(t)xr"(t)=0? How to find r'(t)xr"(t) and r'(t)^3?
     
  2. jcsd
  3. Jan 17, 2015 #2

    Mark44

    Staff: Mentor

    Yes.
    r'(t)r''(t) = 0, which you already found. What is |r'(t)|? Note that this means the magnitude or length of r'(t).
     
  4. Jan 18, 2015 #3
    So how do I find abs(r'(t))? That's where I got stuck.
     
  5. Jan 18, 2015 #4

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    The notation |r'(t)| does not mean the absolute value of r'(t), it means to find the magnitude of the vector r'(t). Think Pythagoras.
     
  6. Jan 18, 2015 #5

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    The problem is that Math10 quoted the formula using abs() instead of modulus.
    It should be ##k(t)=\frac{|\dot{\vec r}(t)\times \ddot {\vec r}(t)|}{|\dot{\vec r}(t)|^3}##
     
  7. Jan 18, 2015 #6

    Mark44

    Staff: Mentor

    Three of us have told you that |r'(t)| does not mean "absolute value". It means "magnitude" or "length" of the vector r'(t).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Find the curvature?
  1. Finding the Curvature (Replies: 2)

  2. Finding Curvature (Replies: 4)

Loading...