diff --git a/elastica/experimental/interaction.py b/elastica/experimental/interaction.py
index 253688971..cd2c86266 100644
--- a/elastica/experimental/interaction.py
+++ b/elastica/experimental/interaction.py
@@ -3,11 +3,11 @@
 
 import numpy as np
 from elastica.external_forces import NoForces
-from elastica.interaction import (
-    find_slipping_elements,
-    apply_normal_force_numba_rigid_body,
-    InteractionPlaneRigidBody,
+from elastica.contact_utils import (
+    _find_slipping_elements,
 )
+from elastica.contact_functions import _calculate_contact_forces_cylinder_plane
+from elastica.interaction import InteractionPlaneRigidBody
 
 from numba import njit
 from elastica._linalg import (
@@ -66,7 +66,7 @@ def apply_forces(self, system, time=0.0):
         )
 
 
-@njit(cache=True)
+@njit(cache=True)  # type: ignore
 def anisotropic_friction_numba_rigid_body(
     plane_origin,
     plane_normal,
@@ -93,7 +93,7 @@ def anisotropic_friction_numba_rigid_body(
     (
         plane_response_force_mag,
         no_contact_point_idx,
-    ) = apply_normal_force_numba_rigid_body(
+    ) = _calculate_contact_forces_cylinder_plane(
         plane_origin,
         plane_normal,
         surface_tol,
@@ -122,7 +122,7 @@ def anisotropic_friction_numba_rigid_body(
         + kinetic_mu_backward * (1 - velocity_sign_along_axial_direction)
     )
     # Call slip function to check if elements slipping or not
-    slip_function_along_axial_direction = find_slipping_elements(
+    slip_function_along_axial_direction = _find_slipping_elements(
         velocity_along_axial_direction, slip_velocity_tol
     )
     kinetic_friction_force_along_axial_direction = -(
@@ -151,7 +151,7 @@ def anisotropic_friction_numba_rigid_body(
         + kinetic_mu_backward * (1 - velocity_sign_along_binormal_direction)
     )
     # Call slip function to check if elements slipping or not
-    slip_function_along_binormal_direction = find_slipping_elements(
+    slip_function_along_binormal_direction = _find_slipping_elements(
         velocity_along_binormal_direction, slip_velocity_tol
     )
     kinetic_friction_force_along_binormal_direction = -(