system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do long rivers work?

The Mississippi River is 2,320 miles long and only drops 1,475 feet in elevation over that length, an average of 7.6 inches per mile. It seems like the water shouldn't be able to keep flowing with such a minor elevation change.
gpt
Why wouldn't it? The water that gets into the river from its surroundings needs to get somewhere (because water tries to spread in all directions) and ultimately, when the river is filled with water, the only possible way for the water to flow is in the direction of the drain no matter how small the elevation drop is.