принуждать vs вынуждать

What is the difference between принуждать vs вынуждать (to force s.o., to compel s.o.)?

Thanks is advance :-)

As I understand it, принуждать is when you're forced by someone to do something that you'd rather not do; вынуждать is something that you're forced to do by circumstance, by something other than a person. ...am I making sense :) ?

For example, "Пилот был вынужден на аварийную посадку из-за неисправности в двигателе."

"В Харькове учителей принуждают голосовать за Януковича" - couldn't think of anything appropriate. This one's from yandex.

Yeah, I think you're right basically. But a person can вынудить as well.
My try:
вынудить кого-то = to put someone in that conditions when he has no choice
(он постоянно опаздывал на работу, часто приходил пьяный, иногда не приходил вообще, он вынудил меня уволить его)
принудить кого-то сделать что-то = to make someone do something (like by force)
быть вынужденным = to have no choice

JFYI: принуждать is a formal word, a spoken version is заставлять.

So as a bottom line you can think that:

"принуждать" means "to force someone to do something directly "

while

"вынуждать" basically means "to make curcumstances that will force somebody to do something", i.e. to force indirectly

Another example to compare two words

"Вася принуждает младшего брата делать зарядку."

So the fabula here is that Vasya says his brother something like, 'If you won't do the morning exercises, I'll beat you hardly'

OR

"Вася вынуждает младшего брата делать зарядку"

Here Vasya might tell his brother, 'Hey, I'm strong and you are loser. And you'll be loser forever'. So his brother just can't stand it and ries powerlifting :)