Merge pull request #454 from RocketPy-Team/doc/fix-positions-document…

…ation

DOC: fix positions and coordinate system documentation page

docs/user/positions.rst

@@ -58,7 +58,7 @@ And with ``coordinate_system_orientation = nose_to_tail``:
 
 .. important::
 
-  - The coordinate system origin is the point where the axis intersect. This
+  - The coordinate system origin is the point where the axes intersect. This
     point is not explicitly specified and can be chosen by the user. All 
     positions given by the user must be relative to this point.
   - The coordinate system origin does not need to be inside the rocket. It can
@@ -102,13 +102,13 @@ the coordinate system origin at the center of mass without motor:
 
 .. important::
 
-  - The coordinate system origin is at the tip of the nose cone. This point is
-    not explicitly specified and can be chosen by the user. All positions given
-    by the user must be relative to this point.
-  - Since the coordinate system origin is at the tip of the nose cone, the
-    position of the nose cone is **zero**. 
-  - We are using the ``nose_to_tail`` coordinate system orientation. This means
-    that the ``center_of_mass_without_motor`` is positive.
+  - The coordinate system origin is at the center of mass without motor. This
+    point is not explicitly specified and can be chosen by the user. All
+    positions given by the user must be relative to this point.
+  - Since the coordinate system origin is at the center of mass without motor,
+    the position of the ``center_of_mass_without_motor`` is **zero**.
+  - We are using the ``tail_to_nose`` coordinate system orientation. This means
+    that the position of the nose cone is positive.
 
 .. _addsurface:
 
@@ -226,15 +226,15 @@ an arbitrary point and the
 
 .. note::
 
-  Liquid motors are do not have the ``grains_center_of_mass_position`` parameter.
+  Liquid motors do not have the ``grains_center_of_mass_position`` parameter.
 
 .. figure:: ../static/positions/nozzletocomb.png
   :align: center
   :alt: Rocket coordinate system origin
 
 .. note::
 
-  We have, in this case:
+  In this case:
 
   - ``nozzle_position`` is negative.
   - ``grains_center_of_mass_position`` is negative.
@@ -248,15 +248,15 @@ And with ``coordinate_system_orientation = combustion_chamber_to_nozzle``:
 
 .. note::
 
-  We have, in this case:
+  In this case:
 
   - ``nozzle_position`` is positive.
   - ``grains_center_of_mass_position`` is positive.
   - ``center_of_dry_mass_position`` is positive.
 
 .. important::
 
-  - The coordinate system origin is the point where the axis intersect. This
+  - The coordinate system origin is the point where the axes intersect. This
     point is not explicitly specified and can be chosen by the user. All 
     positions given by the user must be relative to this point.
   - The coordinate system origin does not need to be outside the motor. It can