The hydrodynamics of how cats drink.
But recent high-speed videos made by this team clearly revealed that the top coat of the cat's tongue is the only open to reach 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 insidious and elegant. The smooth tip of the tongue barely brushes the rise of the liquid before the cat rapidly draws its tongue back up. As it does so, a pillar of milk forms between the moving tongue and the liquid's surface. The cat then closes its mouth, pinching off the top of the tower for a nice drink, while holding its chin dry.
The liquid column, it turns out, is created by a fragile balance between gravity, which pulls the liquid back to the bowl, and inertia, which in physics, refers to the disposition of the liquid or any matter, to keep moving in a direction unless another force interferes. The cat instinctively knows exactly how quick to lap in place to counterbalance these two forces, and just when to end its mouth. If it waits another fraction of a second, the power of gravitation will overtake inertia, causing the tower to break, the fluid to come backward into the bowl, and the cat's tongue to follow up empty.
You really must hold out the videos at the link.
With these videos slowed way down, the researchers established the fastness of the tongue's movement and the frequency of lapping. Knowing the sizing and swiftness of the tongue, the researchers then developed a mathematical model involving the Froude number, a dimensionless number that characterizes the proportion between gravity and inertia. For cats of all sizes, that number is almost exactly one, indicating a complete balance.
So cats' tongues have a Froude number of near-unity. That is pretty darn cool. Now I'm just trying to flesh out whether it makes sense that they modeled the knife as an impeller tip, or what.
12 November 2010 in Engineering, Science (Biology) | Permalink
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