The white Rhino

What is the difference between violence and physical force? Can someone use violence in an attempt to prevent a crime from being committed? For example, would a person be justified (morally, ect) if that person knew about another person's plan to cause harm to another person? Where are the boundaries between violence and physical force? Also where would this fit in with natural law? Please educate me.

I just wanted to give a big shout out to Stefan Molyneux for all the hard work and effort he's put in into all of his videos. I recently started watching his videos a few weeks ago and I was at first skeptical about him and his presentations. After fact checking his sources I was hooked and I look to him to help guide me towards the truth. In fact my favorite video is the Gene wars series. He has helped break the "Brainwashing" that government schools call education as I was a staunch Marxist till I was 17. That's when a lightbulb clicked on and said none of these things work in real life. So if you read this Stefan, thank you very much!! I look forward to all of your videos and presentations; I hope to be on one of your shows as well!!