Did you know that an apple can actually change shape? Believe me, it can--but only with help from a high-tech computer and a "sonic driver."

Both are tools used in an experiment I saw done about three years ago at ARS' Instrumentation and Sensing lab in Beltsville, Maryland, shown below.

There, I met with scientists Judith Abbott and Renfu Lu. They were experimenting with "sonic testing." This test measures how firm an apple is by sending pulses of low-frequency sound into it.

Oddly enough, sonic testing also changes the apple's shape. It causes an everyday kind like Golden Delicious to shake, shimmy and twist about.

This fruity dance only lasts a split second--way too fast for the human eye to see. But with help from a computer animation program, you can catch an instant replay of the virtual apple--in 3–D!

And let me just say that the apple I saw jiggling around on that computer screen didn't look like anything I've chomped on before.

Click here, and see for yourself.

Pretty cool, huh?

Sonics measures the apple's firmness based on how the core, skin and flesh vibrate at certain frequencies. A familiar example is the vibration of a tuning fork or thumping the side of a watermelon.

The changes in the apple's shape are slight, starting with a slight lengthening of its top and bottom. Then the apple looks like it's shrinking in the middle, before returning to normal again. After that, the apple's ends seem to bulge slightly—like a water balloon grabbed at the center.

This all happens in a few seconds.

What's the computer's role in all this? It helps slow things down, and it exaggerates the movements of the apple.

When struck by the sound waves, the fruit vibrates at many different speeds—or frequencies. Each frequency is detected by a device called an accelometer. The computer picks out the frequency that vibrates the apple most. From this it can tell how firm the apple is. Aren't computers neat?

This test could offer a fast, new way of sorting through hundreds of thousands of apples or other fruit on its way to market. Why is this so important? Click here to find out.

The way fruit is tested now for ripeness isn't so gentle. One gizmo, for example, measures how much force is needed to punch two holes in the apple. What's left looks like a vampire attacked.

If it's done correctly, sonics won't bruise the apple, no matter how many times you use it.

Today, Abbott and Lu are busy with new research projects. But other scientists have begun using their sonic testing techniques. In Oklahoma, Israel, Japan and Belgium, for example, researchers are adapting the technology to peaches, melons, cantaloupes.

Will sonics make these fruity favorites shimmy, shake and twist like an apple? That remains to be seen.

--By Jan Suszkiw, Information Staff, Agricultural Research Service