Everything difficult about Fart Together comes from one design decision: the raft is shared and your inputs are physical rather than commanded. There is no "steer left" button that overrides a teammate. Understanding how the physics actually resolves is the difference between a group that clears a course and a group that spends ten minutes arguing about who broke it.
When you push, you are applying a force to the hull at a point in time. That force has a direction and a magnitude and it persists for a moment before other forces act on it. In practice this means the raft's motion is the accumulated sum of what every player did over the last couple of seconds - which is why the boat keeps moving in the direction you last pushed even after you stop.
The critical consequence: inputs do not average out. If you push left and a teammate pushes right with equal force, the expected result is a boat pointing forward. The actual result is a boat that has been torqued in both directions and is now spinning, shedding speed in the process. Compounding beats cancelling, and that is the whole game.
Three separate inputs matter, and confusing them is the most common way a new group loses a run:
Since there is no engine, power is also your brake. Releasing gas bleeds speed off slowly, and actively pushing backwards to slow down bleeds it off faster - at the cost of throwing the raft's heading off whatever it was. Deceleration is a negotiation too.
The lurch is the failure mode every group meets: the raft is travelling cleanly, two players react to the same obstacle at slightly different moments, and the hull snaps into a spin that dumps all the speed. The recovery instinct - everyone pushing to correct at once - is exactly wrong, because four simultaneous corrections is four times the torque.
The recovery that works is one player calls it, one player acts. Everybody else stops pushing for a beat, lets the spin bleed out, and then a single push in the agreed direction resets the heading. This is a communication problem more than a reflex problem, and it is why voice chat makes such a large difference in this game.
The studio is upfront that the raft does not perfectly simulate real-life raft physics - "In fact, we probably shouldn't say that at all" - and that the deliberately loose feel is where much of the comedy lives. Some players find unfair bounces frustrating, and the developers have indicated that per-group-size balance is still being tuned in Early Access. Expect the physics to shift between updates.