One of those 'executive toys' that were big a few years back, which aim to show off a principle of physics or science. Some of us choose to use the cruder name: Newton's Balls, while it has also been named Kinetic Balls.

The aim was to show the principle of conservation of momentum.

This was one of the more interesting executive toys, as it did things which were in some ways counter-intuitive. When set in motion, it produced a rhythmic clacking sound. Depending on your perspective, that was either pleasant and soothing, or irritating to the point of migraine-production.

In its classic form, the toy comprises a framework along the lines of the Olympic parallel bars apparatus, but usually smaller. The parallel bars are connected together to make a frame. A solid metal ball is suspended from the frame by two light strings, one running to each of the two parallel bars. The two strings form a V-shape, allowing the ball to move like a pendulum, but its movement is restricted to the plane that bisects the parallel bars.

The classic toy used five balls. I guess because that shows all the principles, while still keeping the toy reasonably cheap. Maybe senior executives had seven balls compared to the junior executive's five. I prefer to think those hotshots just have bigger balls. However large or numerous they are, the balls end up aligned in a row down the middle of the toy.

The ball on each end is free to move in an arc as one half of its pendulum swing. Pull it back, release it and it falls under gravity to the line of balls. It hits the remaining four balls with a satisfying clack. Immediately, the ball at the other end flies upward, while the original ball simply sticks to the others like glue, with no rebound or other reaction.

After flying outward, the other ball returns to connect with the line of balls and with another clack, the process repeats. There are few losses in the system, so the clack-clack-clack motion repeats for twenty or thirty cycles, before it all goes quiet and needs another swing.

A single ball is no fun

Swing two balls instead of one. As before, they make contact with the line of stationary balls. This time, however, two fly out from the far end -- conservation of momentum. Swing three balls and something interesting happens. The middle ball seems to swings normally, while the two on the outside switch from left to right. If you focus only on the middle ball, it seems to push the other two out to the side.

Lift the two end balls away from the pack and release them simultaneously. What happens?

Now lift two at one end and one at the other and release them at slightly different times. Not a steady clack-clack-clack, but a more complicated rhythm.

Newton's Balls, what's that all about?

Sir Isaac Newton did not have one of these, so far as anyone knows. The idea, according to many sources across the internet, came from an actor and radio newsreader called Simon Prebble, who, in 1967 made beautifully-crafted wooden versions for sale in London's top shop for Toffs, Harrods. Although sales were slim, some marketing people (Richard Loncraine and business partner Peter Broxton) took the idea on and gave it some chrome-plated bling. That helped, but the key selling point was John Noakes who, apparently showed the item no less than three times in 1969.

The connection with Newton is tenuous. I guess the toy gives a great visualisation of the conservation of momentum, but Newton didn't really formulate that law. Old Isaac had three laws named for him, the first says nothing changes velocity unless acted on by a force. The second says the acceleration is proportional to the applied force while the third says every action has an equal and oposite reaction. Newton worked out all kinds of things in his Principia, but I'm not sure the conservation laws were among them. It's quite easy to derive the necessity for conservation of momentum from Newton's three laws, but there's no clear evidence he ever did that. Wiki thinks it was Leibniz who first formulated a modern expression of that law and I see no reason to enter into that discussion. But I digress.

The hand that rocks the (world's biggest) cradle

Wiki also tells us of the world's biggest set of balls. Up to twenty full-sized bowling balls lined up in the classic cradle arrangement, suspended from girders by aircraft grade steel cables. To be honest, they usually only run it with 16, as the building shakes a bit too much with all 20 in operation. This also leaves four spares in case of a disaster, but it still looks impressive, even on a web page.

"The problem," according to builder, Mark Broker, "was having the balls to build it."

After a number of trials, the team started working with AMF, a leading supplier of bowling balls, and AMF made them a set of 20 balls matched for weight (15lb each) and size and internal composition.

I can't find a video on the web, but the website (the Geek Group) is listed below, and the installation is at 2309 N Burdick St, Kalamazoo, Michigan.

The guys at Geek Group say,

"In the 2008 season we are working to secure a larger facility for the cradle and rebuild it to an even larger setup with higher-weighted balls and many more of them. We hope to not only set a world's record with this, but to break our own existing record."

Sources, further information's_cradle


Balls - 20 Ball - 9