class_docstr: The class used to define vectors.
  
  It along with ReferenceFrame are the building blocks of describing a
  classical mechanics system in PyDy and sympy.physics.vector.
  
  Attributes
  ==========
  
  simp : Boolean
      Let certain methods use trigsimp on their outputs
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docstr: Returns the free symbols in the measure numbers of the vector
  expressed in the given reference frame.
  
  Parameters
  ==========
  reference_frame : ReferenceFrame
      The frame with respect to which the free symbols of the given
      vector is to be determined.
  
  Returns
  =======
  set of Symbol
      set of symbols present in the measure numbers of
      ``reference_frame``.
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code: def free_symbols(self, reference_frame):
      """Returns the free symbols in the measure numbers of the vector
      expressed in the given reference frame.
  
      Parameters
      ==========
      reference_frame : ReferenceFrame
          The frame with respect to which the free symbols of the given
          vector is to be determined.
  
      Returns
      =======
      set of Symbol
          set of symbols present in the measure numbers of
          ``reference_frame``.
  
      """
  
      return self.to_matrix(reference_frame).free_symbols
  
imports: from sympy import S, sympify, expand, sqrt, Add, zeros, acos, ImmutableMatrix, simplify
  from sympy.simplify.trigsimp import trigsimp
  from sympy.printing.defaults import Printable
  from sympy.utilities.misc import filldedent
  from sympy.core.evalf import EvalfMixin
  from mpmath.libmp.libmpf import prec_to_dps
label_desc: Use image node_id 33 for calling the Vector obj's underlying member method code with example usage: obj.free_symbols(reference_frame) and returns: self