Force, compel, coerce, constrain, oblige are comparable when meaning to make a person or thing yield to the will of a person or to the strength or power of a thing.
Force, the ordinary and most general word in this group, implies the exertion of strength, typically physical strength, or the working of something (as circumstances or logical necessity) analogous in moving power or effectiveness to such strength.
Sometimes the term takes a simple object, naming the person forced or the thing brought about by force; in such cases the verb often carries additional implications acquired from its idiomatic use in a particular phrase; thus, to force a woman is to rape her; to force a door is to break it open; to force laughter or a smile or tears is to make oneself laugh or smile or cry against one’s will; to force bulbs is to hasten their development by artificial means.
Compel differs from force chiefly in typically requiring a personal object; any other type of object such as a reaction or response is possible only in extended or poetic language when the specific connotations of compel (as the exertion of irresistible power or force or a victory over resistance) are to be carried by the verb.
Compel commonly implies the exercise of authority, the exertion of great effort or driving force, or the impossibility for one reason or another of doing anything else.
Coerce suggests more severity in the methods employed than compel does; commonly it connotes the exertion of violence or duress or the use of threats or intimidation.
Constrain stresses more than does compel, its closest synonym, the force exerted by what presses or binds; it usually suggests the influence of restrictions, self-imposed or placed upon one by force, by nature, by necessity, or by circumstances, that compel one to do a stated or implied thing, live a stated or implied way, or think certain thoughts.
Oblige usually implies the constraint of necessity, sometimes physical necessity, but equally often moral or intellectual necessity. The term also is used with reference to a person or thing which is regarded as authoritative or as having the right to determine one’s course or acts.