It's to do with liquid pressure. The top of the liquid's surface has lower pressure than the bottom of the liquid, so when you pour with the container's mouth on top, there's less force being exerted on the expelling liquid, resulting in a lower rate of flow. As such, it becomes easier to control the flow of the liquid and there will be less spillage.
If you are to pour with the container's mouth at the bottom, the liquid experiences higher pressure, resulting in a greater rate of liquid flow, causing spillage.
An easier way to see this happen is to take a full bottle of water and punch holes on the top, the middle and the bottom. Notice that the water flow at the bottom goes the furthest while the water flow on top goes the shortest.
You forgot to mention what causes the liquid to flow irregular is the way air fills the container. With the mouth at the bottom it enters in the form of bubbles, causing the flow to be irregular. With the mouth at the top air flows in a constant amount it won't cause major flow discontrol. That's why the more empty the container is, the easier is to avoid spillage when serving the wrong way.
...Or you can pour slowly, even with the lip on the bottom end. Once there's sufficient flow going, you just need to keep it steady so the airflow isn't interrupted.
I find that having the lip on top is harder to pour, but that usually happens when you've got too little liquids in the carton to start with.
...Or you can pour slowly, even with the lip on the bottom end. Once there's sufficient flow going, you just need to keep it steady so the airflow isn't interrupted.
I find that having the lip on top is harder to pour, but that usually happens when you've got too little liquids in the carton to start with.
When that happens, it is safe to pour from the bottom. Just take into account of the airflow, like what rom collector said.
