class_docstr: A single degree of freedom translational forced mass-spring-damper.
  
  Notes
  =====
  
  This system is well known to have the governing equation:
  
  .. math::
      m \ddot{x} = F - k x - c \dot{x}
  
  where $F$ is an externally applied force, $m$ is the mass of the particle
  to which the spring and damper are attached, $k$ is the spring's stiffness,
  $c$ is the dampers damping coefficient, and $x$ is the generalized
  coordinate representing the system's single (translational) degree of
  freedom.
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code: def test_force_acuator(self):
      stiffness = -self.k * self.pathway.length
      spring = ForceActuator(stiffness, self.pathway)
      damping = -self.c * self.pathway.extension_velocity
      damper = ForceActuator(damping, self.pathway)
  
      loads = [
          (self.attachment, self.F * self.frame.x),
          *spring.to_loads(),
          *damper.to_loads(),
      ]
      self.kanes_method.kanes_equations(self.bodies, loads)
  
      assert self.kanes_method.mass_matrix == self.mass_matrix
      assert self.kanes_method.forcing == self.forcing
  
imports: import pytest
  from sympy import S, Matrix, Symbol, SympifyError, sqrt
  from sympy.physics.mechanics import ActuatorBase, Force, ForceActuator, KanesMethod, LinearDamper, LinearPathway, LinearSpring, Particle, PinJoint, Point, ReferenceFrame, RigidBody, TorqueActuator, Vector, dynamicsymbols
  from sympy.core.expr import Expr
label_desc: Use image node_id 2 for calling the TestForcedMassSpringDamperModel obj's underlying member method code with example usage: obj.test_force_acuator() without return types