Tea - Mystery in a Cup of Tea

Image credit: NASA Honey injected into water during the MFMG experiment onboard the International Space Station, March 2003.

There's a number in fluid physics theory called "the square gradient parameter" or k. It's proportional to the strength of intermolecular forces between two different fluids, like honey and water. "How two fluids behave when mixed in low-gravity is going to depend on k," says Pojman. "We've never been able to measure k on Earth for a pair of miscible (mixable) fluids. It's value could be anything! But just from watching the video of MFMG we've got an upper limit on k - it must be less than 10^-8 Newtons."

He reached this conclusion in the following way: If k were much greater than 10^-8 Newtons, honey blobs injected into water would quickly assume a spherical shape. But they didn't. The blobs, squeezed into elongated shapes as they passed through the nozzle of the syringe, remained elongated.

"The fact that we could do this using only odds and ends onboard the space station is encouraging," says Pojman. A similar procedure could be used to set limits on, or actually measure, k for many different pairs of fluids.

Some fluids are more important than others. Pojman is most interested in monomers and polymers that might be used in space manufacturing. Such fluids are simpler, internally, than honey, so they might lend themselves to "cleaner" measurements of fluid physics constants.

It's unlikely, though, than any of those other fluids will be as much fun, or mesmerizing, as honey. Who knows what new physics lies in its sweet spinning "smoke rings" or gooey dancing ribbons? It's something to think about the next time you're relaxing with a cup of tea … and you reach for the honey.

Author's note: The kitchen-science experiment described in the opening passages of this story is best done using a "honey bear" - a plastic honey-filled bear with a nozzle on top, available in most supermarkets - microwaved for about 30 seconds. The warmed honey flows easily through the nozzle with a viscosity only a little greater than water. Squirt the honey, gently, into a transparent cup filled with cool tap water. You'll soon see rings and a variety of other weird shapes.