Some cups, etc are easy to pour from, even without lip designed for pouring. While other cups make a mess. Is it just the thickness of the the lip? I feel like coffee cups are particularly bad.
In: 7
Water, because it’s pulled down by gravity, will always want to find the lowest point it can reach without being stopped, but it also really likes to slightly stick to other materials. Which we call adhesion.
So if you have a drinking mug with a round lip, the water will want to go down, but it will also cling to the side of the mug as it does so, cause it’s still going down like that.
But if you have a container with a pouring lip, the water can’t do that, because in order to cling to the side of the container, it will have to travel up again past the underside of the pouring lip. And because the water is pulled down by gravity, it can’t go up, so it has no choice but to fall straight down.
Think of a sagging clothes line that’s collecting dewdrops. From the side the droplets will travel to the middle, because they’ll go down that way, but once at the middle they would have to go up again so they have no choice but to fall off the clothes line.
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