I am rich now, friends.

[JohnDG]

Go outside and punch somebody in the face. You will get an equal (punch) and opposite (person) reaction.

Well.. how hard did I punch them?

Well, if it takes 9 pounds of force to break a bone, equivalent to about 40 Newtons.

So if an average arm is 3.16kg roughly, then we can calculate;

So given A = F/M, 40/3.16 = 12.65 (12.65 Newtons/kilograms = 12.65 (kilograms meters/second2)/kilograms = 12.65 meters/second2)

If you can manage 12.65 meters per second from your fist (or almost 30 miles per hour) I can almost guarantee there will be no reaction from the person I punch as we break a bone in their face.

If I punch correctly and introduce my own bodyweight behind the punch, combined with inertia of the swing, I might even be able to get this down quite low.

So if you manage to get the math right, you can certainly ensure that you will not get an equal (punch) and opposite (person) reaction as they cry on the floor with a broken face (despite the likely broken hand as well of course).

Just sayin', mathematical truths applies to anecdotes too.

(BTW Maths and Physics majors.. please don't cringe too much.. )

I hope you don't spend time dwelling on this kind of stuff during an actual fight.