This variable can be used to set whether or not the instance can
be affected by rotational forces (default is false). If
this is set to true, no external force (either from coded
impulses or forces, or from collisions) will affect the rotation
value of the instance and this would have to be set manually using
phy_rotation = 0;
phy_fixed_rotation = true;
The above code will switch the instance to have a fixed rotation, then set the rotation angle.