Ketchup, My Favorite Non-Newtonian Fluid

Ketchup, My Favorite Non-Newtonian Fluid

When the ketchup won't come out of the bottle, simply tilt the bottle at about a 45 degree angle and tap it gently against the heel of your hand.
I have been using a lot of ketchup lately, ever since scoring a few bottles of the new Heinz Balsamic Vinegar version. Ketchup has many excellent qualities, of course: for one thing, it embodies a wide spectrum of flavors including salty, sweet, and umami. 
 
For another thing, ketchup is one of the world's few examples of a fascinating physics phenomenon, non-Newtonian fluids. And the more you understand how a non-Newtonian fluid works, the more easily you will be able to get ketchup out of a glass bottle without a hitch!

We all know what fluids are. They are, you know… fluids. Your basic fluid is technically a Newtonian fluid, which means that its viscosity increases in direct relationship to the pressure applied to it. That's a fancy way of saying that Newtonian fluids flow in a predictable fashion, regardless of how much pressure they are under. Think of the water at the bottom of the ocean, which is under tremendous pressure - but it still flows. As does the water vapor high in the atmosphere, where air pressure is almost non-existent.
 
Non-Newtonian fluids, on the other hand, have an unpredictable viscosity. In a Newtonian fluid, the harder you push, the thicker it becomes. A non-Newtonian fluid doesn't follow this rule. 
 
Take ketchup, for example. I have a half-full bottle sitting here beside me. If I pick it up by the neck and shake it rapidly back and forth, the ketchup inside behaves like a thick fluid: it sloshes side to side. But if I quickly turn the bottle upside down, the ketchup stays stuck there at the bottom (now the top), in seeming defiance of gravity. But if I then tap the side of the bottle against the heel of my free hand, the ketchup returns to a more fluid form, and begins to slide down the side.
 
One of the most dramatic examples of the physics of non-Newtonian fluids happened on Mythbusters. The team filled a swimming pool with a bluish mixture of corn starch and water. Slip slowly into the pool and you sink in. But slap it hard - or run across it quickly - and it becomes almost a solid.
 
The answer to the age-old ketchup frustration is thus provided by physics. When the ketchup won't come out of the bottle, simply tilt the bottle at about a 45 degree angle and tap it gently against the heel of your hand. This will return the sauce to a liquid, and presto, your fries are delicious again!