Why does water go gluglugglug when we pour it too fast? Will it take a shorter time to empty the container if we pour a bit slower?
In: Physics
Imagine pouring water out of a bottle. This was probably what you thought about because it happens mostly with bottles, I have never seen it happening with a bucket.
So, there is a small opening and bigger space behind that little hole. If you pour water holding the bottle in about 90°, half of the hole is filled with water, and half is filled by air. Both are flowing, there is nothing to stop them, it’s easy for them to change places.
But if you tilt the bottle so the whole opening is covered with water, there is a little… battle. Water is trying to escape from the bottle but another end of the opening is covered with air, which creates a “wall” that the water is breaking rather easily because it’s heavier. It’s harder to the air and the water to change places because they are in the way of each other. A little bit of water breaks through the air wall, so a bit of water goes out od the bottle, creating space for air to get in. It creates a bubble. And again, and again. That process makes the gluglugglug sound and also the feeling of the bottle moving like glugglugglug. It’s about pressure. As soon as there is too few water to cover the opening, it stops gluglugglugging because both the air and the water can flow and change places easily.
It’s really easy to imagine if you think about humans! If there are two big rooms connected with a narrow corridor, and there are people in both rooms and they need to change places.
If there is one person in room A, and one person in room B, they can easily pass next to each other in the corridor and.
If there is a lot of people in both rooms and they change places slowly, let’s say 5 people of each group going calmly through the hall, it’s easy.
If they want to change places instantly and both groups are rushing to the narrow corridor, they will bump onto each other and it will be hard to move, but they would gluglugglug a bit (lmao) and they would finally change places. As there is fewer and fewer people in the corridor, it’s becoming easier to go through it and there is no need to mess with anyone.
Glug glug from a bottle or jug happens because the water is coming out and air is going in.
If you pour it slower it will take longer to empty.
Your best bet is to place a hole on the top opposite where you’re pouring, so air can get in separately from where the water is pouring out. I do this with boxes of broth.
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When water leaves the container, something has to fill that space back up because it can’t just be “nothing”. If you’re just standing there pouring the container out, then air is what’s going in to fill the space.
If the container only has a single hole, and the water coming out fills the entire opening, then there’s no room for the air to get in. That means the empty space can’t get filled back up with air, so it’s filled with “nothing” – otherwise known as “vacuum”. The vacuum pulls the water back up…which makes a small space in the opening…which lets air rush in to fill the vacuum…which lets water start flowing again…which fills the opening…which blocks air from entering…etc.
Each “glug” is one cycle of “water out, vacuum stops it, air rushes in, water out again”.
If you’re able to pour out of the container in a way that prevents the water from filling the entire opening at once, then you’ll find that there is no glugging.
In order for water to get out of the container, air has to get in to replace the lost volume. Otherwise you end up with a vacuum in the container and the water gets sucked *in*, not out.
If you pour normally, the water comes out the lower part of the opening and air goes in (at the same rate). But if you pour too fast, the water fills too much of the opening and the air starts to meaningfully speed up to get through the opening. This causes the pressure in the opening to drop, which pulls the water up to fill the opening. Once the water fully fills the opening it’s all water out, no air in, so you start to build a vacuum in the container. Once this gets strong enough to reverse the flow, the water stops and you get a “glug” as a slug of air gets pulled into the container. Now the water charges forward, plugging the opening again, and the cycle repeats…glug, glug glug.
You almost always get a faster total flow by going just up to, but not over, the “glug point”.
There’s only one hole in the container, and air has to get in to occupy the space being freed up by the water coming out, so if you pour too fast you get a glob of water going out, then a similar amount of air getting sucked in, then a glob of water, etc. Yes, it would probably empty the container faster if you didn’t tilt it far enough to completely block the outlet, because then air can come in at the same time as the water leaves.
Because air has to fill the empty space the water leaves behind it. If you have a container with another hole large enough to suck air in behind the water (while the contain is pouring), it’ll pour faster and not have the mentioned issue.
Alternatively if you can spin the container for form a vortex as the water pours out, it’ll also pour faster because air can go through the middle of the vortex instead of the water having to temporarily stop so air can flow through.
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