A block slides on an inclined plane.
When the user checks the appropriate option, the "hill" is removed and replaced with two contact forces: FRICTION FORCE and NORMAL FORCE. The contact forces originate at the midpoint of the bottom of the block.
If the user chooses, In addition, a GRAVITY FORCE originates at the center of mass of the block.
If the user chooses, the block may also be removed. The reader should inspect the location of the origins of each force.
Finally, if the user chooses, the block may be collapsed to a particle. Notice the shifting of the origins of the forces, enabled by the point-wise principle of Euclidean Space. The object is a particle, which is the physical analog to a point -- it is infinitesimally small and the mass of the entire body is assume to be at this particle. All forces are assumed to act on the particle. While this shifting is not essential to the solution of the problem, it does demonstrate that care must be taken when decomposing forces.