How Come?

Archive for the ‘food’ Category

Why does a falling piece of toast always seem to land on the buttered side?  asks a reader.

It’s the heartbreak of dropped toast.  You tip your plate or lose your grip or bump the table.  In the blink of an eye, your toast is, well, toast: the buttered side stuck to the floor, its surface studded with dust, grit, and cat hair.

But don’t blame the cow.  Toast also lands jam-side down, peanut butter-side down, and, in the U.K., Marmite-side down.

The falling toast effect is one of the most popular examples of Murphy’s Law:  that whatever can go wrong, will.  People have been dropping their buttered toast on the unforgiving floor (and complaining about it) for centuries.  In 1841, an Ohio newspaper called The Huron Reflector published a bread lament:

“I never had a slice of bread, Particularly large and wide, That did not fall upon the floor, And always on the buttered side.”

By the end of the 20th century, science had caught up with what the rest of us already suspected.  U.K. researcher Robert Matthews conducted a scientific investigation of the dynamics of buttered toast.  The result was a 1995 report in the European Journal of Physics, “Tumbling toast, Murphy’s Law, and the fundamental constants.”

In the paper, Matthews noted that the prevailing view among scientists at the time was that there was no toast problem.  Like flipping a coin, toast dropped enough times should land 50 percent of the time on the plain side, 50 percent on the spread side.

And a BBC science show experiment in the early 1990s seemed to support that conclusion.  Volunteers threw their toast into the air.  Of 300 tosses, 152 landed butter-side down, 148 butter-side up.  The conclusion:  the chances of buttering your floor are about 50-50.

But Matthews found this wasn’t the case.  In real life, toast isn’t tossed up into the air.  Instead, it slips off a table or a plate, and usually does land on the buttered side.

How come?  While it seems like the weight of the butter or other spread is to blame, Matthews says it’s the height the toast falls from that’s crucial.   When toast — resting buttered-side up — slips off a standard-height table, it tends to flip over.  Why?  When the center of the slice — which is the center of gravity, if the toast is buttered evenly — moves beyond the edge of the table, the toast begins to rotate over the edge.

If the distance to the floor isn’t far, the toast won’t have time to do a full 360 in the air.  So toast falling about 3 feet usually lands butter-side down.  If the toast has far to fall, it could go either way:  angular momentum will cause it to spin end-over-end, but air resistance will slow it down.  And if it happens to spin, say, 1.5 times, it’s buttered linoleum all over again.

The tumbling toast effect, Matthew says, “seems to be an ineluctable feature of our universe.”

For more toast experiments, visit www.thenakedscientists.com/HTML/content/kitchenscience/exp/butter-side-down.

What is the hot chocolate effect?  asks a reader.

Did you ever pour a packet of cocoa mix into a cup of hot water…and notice that the pitch of your spoon striking the cup seemed to rise or lower as the mix dissolved?  If so, you’re familiar with the Hot Chocolate Effect.  The strangely musical effect can also occur with instant coffee, or when we add powdered creamer to coffee or tea, spoon sugar into a hot drink, or even drop a scoop of ice cream into a mug of root beer.

To listen for the hot chocolate effect, you’ll need a metal or wooden spoon; use either end.  (You can also use your knuckle, and rap against the outside of the cup.)  After filling the cup with hot water or milk, quickly tap the bottom or side of the cup before adding cocoa.  That way, you’ll tune into the mug’s powder-free sound.

Now add the cocoa, and keep tapping.  You should hear the pitch of the tap first drop, and then begin to rise.  How come?

Physicist Frank Crawford explained why in a 1982 article in the American Journal of Physics.  Crawford dubbed it The Hot Chocolate Effect, and since then, researchers have expanded on his original explanation.  (Read about engineer Kevin Kilty’s experiments with “the cheap instant coffee effect” at www.kilty.com/coffee.htm.)

Scientists say that when you add cocoa to your cup, some of the air dissolved in the hot water gloms onto the powder grains.  The result is tiny bubbles, clinging to the powder.  In other words, foam.  The cloud of foam reduces the speed of sound through the liquid.  Meanwhile, the frequency at which sound resonates inside the mug depends on the sound wave’s speed.  The lower the speed, the lower the frequency.

So when you first add cocoa powder, sounds will actually decrease in frequency.  Since the frequency determines a sound’s pitch, your tapping spoon will sound up to an octave lower than it did in plain hot water.  (Think low thunk.)

But as the bubbles float to the surface and pop, the sound traveling through the cocoa quickly speeds up.  The frequency of the sound begins to rise, and along with it, the pitch.  And so we hear higher and higher notes with each new, now-tinkly tap.  Astonishingly, the pitch can rise up to three octaves, or about the vocal range of a well-trained singer.

(Watch a video of the effect using instant coffee at www.youtube.com/watch?v=JCVaOzlOUfY.)

Experiments to try yourself:  Does the composition (glass, ceramic, plastic) or thickness of the cup make a difference in the changing pitch?  What about a taller or shorter cup or glass?  How about a cup with or without a handle?  (Try tapping on the cup’s bottom, then on or near the handle.)  Does using different liquids (water, skim milk, whole milk) alter the sound?  Finally, what about adding whipped cream or marshmallows?  At the very least, it’s all a good excuse to make a second (or third) cup of cocoa on a cold winter’s day.