Ever have trouble getting ketchup out of the bottle? Well, even scientists aren't sure why it happens!

However you feel about ketchup, one thing is for sure: It has remained a very popular condiment. Its fans are so devoted for the simple reason that they like its taste. But, for some, there is so much more to it.

Scientifically speaking, ketchup is a non-Newtonian fluid. Those types of fluids get thinner or thicker with shear stress. What does that mean in simple and practical terms? Ketchup is in a nearly solidified state when it’s sitting in a bottle. That all changes when pressure is applied and it squirts out, which is an example of shear thinning.

Believe it or not, even with modern technology, there are some things that we do not know about ketchup. The question of why shear thinning occurs is one such example. Is it because particles move in layers and are efficiently streamlined in their paths? It’s possible, but that idea has not been proven. If true, it would also explain shear thickening, which theoretically happens because those layers breakdown, causing particle collisions.

Researchers at Cornell aren’t satisfied with that explanation. Their experiments have helped them conclude that the amount of layering doesn't change enough to account for changes in the behavior of non-Newtonian fluids.

Whatever the truth is, who knew there was so much ado from scientists just trying to figure out why ketchup does what it does?

(Source)