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Are projectile spells like fireball affected by gravity and arc from their origin to their destination, or do they travel in a straight line?
I’d like an explanation from both an official and logical standpoint.
For example can I lob a fireball over a wall assuming there’s no ceiling in the way if I’m also using a spell that allows me to see targets through the wall. I once heard it compared to a catipult and that made me wonder if you could use it similarly.
Really, it shouldn't matter. D&D is not a physics simulator, as tends to get pointed out frequently here, with the additional caveat that they only do what they say they do.
The general rule is really that things like gravity work as expected regarding 'real world' situations, such as its affect on objects and creatures. But anything else, like spells, you just have to go by the rules.
Fireball says:
A bright streak flashes from your pointing finger to a point you choose within range
Emphasis mine. You select the point. That's where the fireball blossoms. How the 'bright streak' moves to this point is irrelevant.
Other rules worth pointing out are the "Clear path to target", which has a tacit assumption that the path is a straight line.
And...regarding areas of effect:
For a sphere (like a fireball):
You select a sphere's point of origin, and the sphere extends outward from that point
Again, pointing out the fact that you simply choose the point of origin.
And for a line:
A line extends from its point of origin in a straight path up to its length
Here, the straight path is explicitly pointed out.
D&D is not a physics simulator and it does not care about arcing or straight lines. There are rules for targeting a spell, and if those are met, the spell can be cast and can hit. It doesn't matter to the game if they arc, travel in a straight line or do a tango dance before reaching, because that makes no difference for the rules.
If for some reason you really wish to know if a fireball arcs or moves in a straight line in your specific game, ask your DM to make a personal interpretation, because they're really the only person at this point who can make a "ruling".
I'll be quoting from the rules as written on D&Dbeyond. Emphasis mine.
Targets
A typical spell requires you to pick one or more targets to be affected by the spell's magic. A spell's description tells you whether the spell targets creatures, objects, or a point of origin for an area of effect (described below).
A Clear Path to the Target
To target something, you must have a clear path to it, so it can't be behind total cover. If you place an area of effect at a point that you can't see and an obstruction, such as a wall, is between you and that point, the point of origin comes into being on the near side of that obstruction.
So no, you can't lob spells over walls, therefore it must be a straight trajectory.
