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!

Degrees of freedom an constraints

  1. Jan 11, 2012 #1
    I'm not quite sure I get the idea of a degree of freedom for a system. First of all: Is there freedom in characterizing the DOF for a system - i.e. will specifying the DOF for a system relative to any coordinate system always be the same?
    Next let me do an example: If we have 2 particles free to rotate about any axis, what is the total DOF for that system? Is that 12 or 6? Because I normally see 6, but isn't that just because you see the particle as a point? On the other hand it perhaps doesn't make sense to say that a single particle can rotate.
    Next let's imagine that we put a constraint on the system saying that the distance between the two particles must stay fixed. I have then been told that the total DOF are 5. But how do I realize that? And does this number account for rotational DOF?
     
  2. jcsd
  3. Jan 11, 2012 #2

    hotvette

    User Avatar
    Homework Helper

    One way to look at this is to ask the question: how many numeric values does it take to completely describe the state of the system? You first have to have some assumptions about valid states: translation, rotation, time, etc.

    In the case of 5 DOF, I am guessing that position is the only valid state (i.e. rotations aren't allowed). In that case, the first particle is described by 3 spatial coordinates. The 2nd particle can be anywhere on a fixed sphere around that particle. In spherical coordinates, r is fixed but theta and phi can be anything, thus 2 extra DOF for a total of 5 DOF.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Degrees of freedom an constraints
  1. Degrees of freedom (Replies: 6)

  2. Degrees of freedom (Replies: 4)

  3. Degrees of freedom (Replies: 2)

  4. Degrees Of Freedom (Replies: 6)

Loading...