system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What determines whether liquid being poured out of a glass is going to pour out and down the side of the glass rather than straight out?
gpt
It's all to do with the speed of the water as it passes over the lip. If the water is moving slowly then it will not overcome the force holding it to the glass (adhesion). However if it moves quickly, the water has more momentum and it can break free and pour away from the glass.

If the water cannot "break free" of the surface then it will simply roll over the lip of the glass and trickle down the outside.

The spout on a jug, you'll notice, curves downward slightly when the jug is held  at a pouring angle. Obviously the more vertical the water stream the faster it flows, so jugs pour nice clean streams if water.