That has happened to all of us at some point squeeze an almost empty ketchup bottle and see how its content explodes out, leaving everything lost around it. It has happened to us, but we may not have asked ourselves why. However, a team of scientists from the Oxford University Yes, you have asked yourself that question, and you have even carried out the calculations to answer it.
It is important to make it clear that the results of your research have so far been published only as preprint. This means that they have not yet undergone the necessary revisions for publication. However, while receiving these reviews, they have presented their work at a conference of the Fluid Dynamics Division of the American Physical Society.
Although it should be taken with caution, it is interesting how they have used science to explain something so everyday. And also to look for solutions, since they have exposed what we can do as users or even what improvements could be introduced by the ketchup makers to prevent this from happening. Okay, it’s not vital research, but at least it’s curious. Science is that too.
Ketchup and the physics of fluids
When we press a ketchup bottleseveral forces intervene, but in this phenomenon two mainly participate.
On the one hand, the air at the top of the container is compressed like a spring, pushing the liquid underneath. Meanwhile, this downward force is resisted by the dragging of the ketchup towards the walls of the container. Now, what happens if there is little ketchup? Well, basically, it’s not enough to contain the downward force, so that compression of the air causes the sauce to come out explosively.
Nothing happens: there is a solution
It should be noted that this investigation was not carried out with a ketchup bottle. In fact, its authors carried out a series of experiments injecting air from a syringe into an oil-filled capillary tube. In this way, they wanted to investigate why a smooth flow of liquid can suddenly end up spraying like a sprinkler.
Chris McMinn, one of the authors of the research, explains in a statement what is happening and how this problem can be solved. “You need to compress the air to generate the motive force to move the liquid, and as the liquid flows, the resistance of the viscosity decreases because there is less and less liquid to push,” he points out. “At the same time, the liquid outlet makes more room for air to expand in the tube, which decreases the driving force over time”.
Therefore, the key is in squeeze gently, to prevent the air from being compressed too much. In addition, they believe that if ketchup manufacturers did the larger nozzles, part of the problem would also be solved, since the viscous drag would be reduced. And it would be solved even more if the valves they have many of these containers. It is true that these are very useful to avoid spills. However, they require squeezing before the ketchup can come out, so the air is further compressed and spattering increases.
To prevent this from happening, the recommendation from MacMinn and his team is remove lid when ketchup is low. Thus, the space is increased so that the ketchup can flow freely and it is not necessary to exert as much pressure. As the Oxford University professor himself points out, this is something we already intuited, but now mathematics corroborates it. Even if the study hasn’t been reviewed yet, we can at least take the lid off by thinking about the physics behind what we do.