Scientists have given the scientific explanation why when you squeeze a ketchup bottle with little ketchup left in it, it always spills out. Fortunately, their work also shows some ways to prevent this terrible event from happening.
Two Oxford University scientists presented their work with the catchy title “The dynamics of compressible displacement in a capillary tube” at the American Physical Society’s Fluid Dynamics Division conference last month.
Using mathematical modeling and a series of experiments, they showed that squeezing the bottle slowly and smoothly will significantly reduce the chance of sauce splashes ruining your favorite decorations. While it all depends on a complex system of fluid dynamics, ultimately this study demonstrates how resistance and power affect how sauce flows from the bottle.
When you squeeze a plastic sauce bottle, the air at the top of the bottle compresses like a spring, pushing the liquid in front of it out. Meanwhile, the downward force is resisted by the frictional force between the ketchup and the walls of the bottle.
For the perfect pour, sauce lovers will need to delicately balance these two forces inside the bottle. However, when the sauce is reduced, this fine balance is disturbed as the drag from the sauce decreases. With less friction, the air in the bottle releases its full potential like a depressed spring, causing the last bit of sauce to be ejected in a sudden explosion.
Study author Professor Chris MacMinn, from Oxford University’s Department of Engineering Sciences, said in a statement: “You have to compress the air to create the driving force to move the fluid. As the fluid flows out, the resistance to viscosity decreases as there is less fluid to push. At the same time, the outflow of fluid, the air into the tube. “It makes more room for it to expand right, which reduces the driving force over time,” he said.
Also from the Department of Engineering Science at Oxford, Dr. “Our analysis reveals that the scattering of a ketchup bottle can be fine-tuned: Even squeezing a little too hard will produce a scatter instead of a steady stream of liquid,” added Callum Cuttle.
In addition to slightly tightening, the researchers suggest manufacturers should make bottle caps with wider nozzles to reduce the chance of splashes. Their work showed that the rubber valves commonly used on sauce bottle caps today are also a major source of the problem: “These valves exacerbate the spillage problem by forcing you to build up a certain amount of pressure before the sauce leaves the bottle. These valves help prevent leaks, but from a purely scattering standpoint it would make a lot of sense to remove these valves. For a quick fix, when you’re near the end of a bottle (when there’s a high chance of spillage), remove the cap and drain any remaining liquid from the wider mouth. That may be common sense, but there is now a rigorous mathematical foundation to back it up.”
The article, which has not yet been peer-reviewed, was recently published on the preprint server arXiv.
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