Which specific law of physics is broken by the "double jump"?

Question

So, there's a cliche in computer gaming known as a "double jump". This can be described as: >A character jumps from a solid surface, and then is able to extend their jump by carrying out the jump action again in mid-air, starting their ballistic arc again from that position. I appreciate that, barring some rocket propulsion, this is not physically possible, but which specific law would have to be suspended in game dynamics in order to allow this to happen?

Answer 1

This type of motion would violate Conservation of Momentum, a fundamental principal of physics that is a direct consequence of combining two fundamental Laws of Nature: Newton's 2nd Law of Motion and Newton's 3rd Law of Motion.