The obvious physics: Forces, F=ma, reaction time, 3rd Class Levers (Arms)
Less obvious physics: Inertia
After my boyfriend and I had just finished watching an excellent, Matrix-style MMA fight between two lightweights named Bensen Henderson and Anthony Pettis, my boyfriend started browsing through previews of other fights. He landed on a preview for a heavyweight fight and both of us just went, "Whoa!"
Me: "Those fights must be epic! They're so strong!"
Boyfriend: "They are slower."
More inertia, eh? I guess I will be brushing up on my MMA fights this school year to find some examples of slower-moving heavyweights and quicker-moving lightweights.