Wordplay: How Newton's Cradle Works

67. Mr. Prebble’s greatest challenge was convincing serious business people to buy something without an apparent purpose. Eventually Mr. Prebble succeeded. The Newton’s Cradle soon became a hit and created the executive toy market.

We present the following update as of 1:30 AM on Sunday, Dec. 12.

The puzzle remains unsolved. The discussion continues.

What do we know? Several things. First of all, Option B is out. If a double-sized ball hits a series of four normal balls the last two balls do not swing out in tandem.

Second, it would seem that in theory all balls would swing out. Especially the last two. The double-sized ball would initiate a series of collisions that would cause the balls to splay. Hans was the first to compute the resultant velocities.

Third, we know the results of several rather informal experiments. These seem to show that the double-sized ball will cause the last ball to swing out alone. The remaining balls don’t seem to move very much. The third and forth balls, in particular, seem to stay surprisingly close together. (Shown is a 9/8? ball swung into a series of 7/8? balls. Here’s the same phenomenon scaled down.)

What’s going on?

The splay pattern below, by the way, was also created using a 9/8? ball and series of 7/8? balls.

Check out The New York Times on Dec. 7 for a special Science Times feature on puzzles. From the introduction:

“This special issue explores a phenomenon that threatens to become a craze: puzzles, ever more ingenious, complex and interactive. We look at the science of puzzles, and puzzles about science.”

The special feature contains articles by Benedict Carey, Pam Belluck, Jennifer A. Kingston, John Schwartz, Denise Grady, John Tierney and Cornelia Dean. You’ll also find an assortment of original bafflers, including several by Wordplay’s Jim Horne and Numberplay’s Pradeep Mutalik. The online version contains addition features including Test Your Insight and Jim Horne’s The Rush of the ‘Crossword Puzzle Moment.’

Much gratitude to Simon Prebble for recounting the origin of the Newton’s Cradle and creating an audio version of the interview.

Thank you as well to Adam Bowman, creator the Newton’s Cradle interactive animation above. To see more of Mr. Bowman’s creations, visit his site.

Pradeep Mutalik will be back next week with another adventure in logic.

Puzzle ideas of your own? Send to numberplay@nytimes.com.

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