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From A New Hope to Revenge of the Sith to The Last Jedi, we see starships blown up in battles in space. The larger ships, like Star Destroyers and Dreadnoghts, don't just blow up, however. They partially explode and fall. Larger structures, like the Death Star, explode. Smaller ships, like X-Wings and TIE Fighters, explode. While we can assume that certain weapons will affect smaller ships differently than their larger counterparts, this disharmony is a bit confusing.

What causes larger ships to 'fall' when blown up in the Star Wars universe?

Typically when you're in space above a gravity well, you stay "up" by falling sideways so fast that you just keep circling around the object/planet. That's what it means to be in orbit.

In Star Wars, we rarely see ships in orbit. They usually just hover over a single place. Rather than moving sideways to stay up, they utilize Repulsorlifts to accomplish this feat, directly counteracting the effects of gravity wanting to pull them down.

When a ship is damaged or destroyed however, the repulsorlifts fail. Since there's no longer anything holding them up against gravity, they then begin to fall back towards the object/planet.

Now, regarding the discrepancy between large and small ships. If you launch a missile at a small ship, the power of the explosion compared to the size of the craft is more than enough to blow it into tiny pieces, wherein the force of the explosion launching those pieces every-which-way is more apparent than the pull of gravity for a time. If you were to take that same missile and launch it at a large ship however, it would do substantially less structural damage relative to its size (and impart less relative force), even if it is still capable of doing sufficient critical damage to disable it.

If a small ship were to take critical damage without being blown to tiny pieces, we should expect it to fall just as larger ships do. This just rarely happens.

Lastly, the Death Star was known as an orbital battle station, and it's almost always in orbit when we see it (Yavin, Endor, Jedha, Scarriff). It would make little sense for a craft the size of a small moon to use repulsorlifts, since it has no need to stop above a planet, or lower/raise itself relative to the surface (it's not like it needs to land). So when it explodes, gravity has no apparent effect, because it's acting equally on it the same as it always had been, continuing to fall sideways. The debris we do see falling and burning up are the parts blown towards the planet by the explosion itself.

Because Star Wars battles are Naval battles, roughly WW2 era.

What you are seeing is those starships "sinking", like how a large naval ship sinks on a planet.

There may be arbitrary in-world justifications for it. But fundamentally it is the same reason why fighters do banking turns and behave as if they are flying through air, and why bombers "drop" bombs.

For the same reasons explosions in space go boom, fighters have wings, and so on*. It's because the writers and directors are either ignorant of physics themselves, or they think they have to appeal to an audience that's ignorant of physics.

*Especially the reason that maybe 99% of Hollywood car crashes result in fires and/or explosions. In the real world, less than 1% of crashes result in fires, and only a small fraction of those result in explosions: https://one.nhtsa.gov/cars/rules/regrev/evaluate/807675.html or visit your local auto wrecking yard and notice how few burned vehicles are brought in.

The Star Wars universe is a movie universe.

The general consensus among movie makers goes like this:

1. Small vessels get blown apart. This is a departure from classic war movie depiction of aircraft destruction, and serves to demonstrate that the weapons involved are very powerful.




2. Giant vessels, such as Death Stars, are the point of space battles, and as their destruction signifies the climax of the battle, their end is, well, climactic. Complete destruction.




3. Merely large vessels, when destroyed, are more visually impressive when the destruction is partial, with an explosion followed by flaming debris. So that's what you get. Here the visual trope is the destruction of capital ships in WWI and WWII.