Wish my doctoral thesis had been this cool on video.

The hydrodynamics of how cats drink.  

But recent high-speed videos made by this team clearly revealed that the top surface of the cat's tongue is the only surface to touch the liquid. Cats, unlike dogs, aren't dipping their tongues into the liquid like ladles after all. Instead, the cat's lapping mechanism is far more subtle and elegant. The smooth tip of the tongue barely brushes the surface of the liquid before the cat rapidly draws its tongue back up. As it does so, a column of milk forms between the moving tongue and the liquid's surface. The cat then closes its mouth, pinching off the top of the column for a nice drink, while keeping its chin dry.

The liquid column, it turns out, is created by a delicate balance between gravity, which pulls the liquid back to the bowl, and inertia, which in physics, refers to the tendency of the liquid or any matter, to continue moving in a direction unless another force interferes. The cat instinctively knows just how quickly to lap in order to balance these two forces, and just when to close its mouth. If it waits another fraction of a second, the force of gravity will overtake inertia, causing the column to break, the liquid to fall back into the bowl, and the cat's tongue to come up empty.

You really must check out the videos at the link.

With these videos slowed way down, the researchers established the speed of the tongue's movement and the frequency of lapping. Knowing the size and speed of the tongue, the researchers then developed a mathematical model involving the Froude number, a dimensionless number that characterizes the ratio between gravity and inertia. For cats of all sizes, that number is almost exactly one, indicating a perfect balance.

So cats' tongues have a Froude number of near-unity.  That is pretty darn cool.  Now I'm just trying to figure out whether it makes sense that they modeled the tongue as an impeller tip, or what.

Comments

[Delores]

so, should we be calling you Dr. Erin? :)

The videos are cool, but I am just thinking about how much "lapping" those cats have to do to just get a bit of milk! I almost feel sorry for them.