Scenes from Return of the King in which physics might be discussed:
- Gollum hanging down towards the beginning
- The arrow fired by Legolas to pierce Wormtongue
- Saruman's plunge
- The distance of the Palantir and how far it rolled
- Sam's fall down the stairs after leaving Frodo, perhaps including the fall of the Lembas crumbs
- Siege towers for the assault against Gondor
- The Witchking's mace; wielding it, dislodging it from the ground, etc.
- Grond and other siege weapons
- The return-fire from Gondor (using sections of their own wall)
- The difference of siege weapons between the lever action of Mordor and the sling-type action of Gondor
- The Nazgul terrorizing the people and weapons on the tops of Gondor...the distance it took for the Gondorian victims to fall before hitting the roofs below
- Bracing the door (brace versus the force from the other side, being banged on by the troll with the hammer) when Gandalf and Pippin are waiting for the breech of the second (third/fourth?) tier gate, when they discuss the white shores
- Denethor's flaming plunge
- How Aragorn, Legolas and Gimli would likely have sustained injuries from their jump off the ship if they'd made it in real life
- Legolas versus the Oliphants...sliding off the trunk and landing unharmed right in front of Gimli
- Aragorn dropping the Evenstar pendant, and its subsequent shattering
- Gollum's fall
- The fall of one of the Dark Riders when his mount is attacked by an eagle
- The destruction of the Dark Tower (Golly, I hope you've already seen the film!
)
Covered enough topics? I'm guessing if you want to narrow in, the siege weapons would be a good thing to go with. It's a topic of physics that still affects battle strategy today, and has several facets of interest in the movie.