Newton's Cradle

The "Newton's Cradle" has been a staple of scientific classroom demonstrations for many decades. Every high-school student has seen one. They are a simple and reliable means of visually demonstrating many of the fundamentals of Newtonian physics. The Geek Group has used them for years as part of our demonstration repertoire with great results.

Since about 2001 we have used our tabletop cradles handcrafted by Mark Broker. They are a matched pair that we use for a demonstration called "Elastic Vs Inelastic Collisions" and we have had them in daily use for lab and classroom demos since Mark built them nearly a decade ago. With the exception of the occasional easily fixed tangle they have never had a failure.

Chris doing a physics demo with the tabletop cradle set made by Mark Broker.

The only problem with them is the same problem we have with all tabletop demos. You can only use them with a rather small crowd. Normally this isn't a big deal, but Newton's Cradles are the kind of thing that EVERY kid wants to touch and play with. The tabletop demos are simply too small and too delicate for a crowd of a hundred rambunctious 9 year olds to be mauling.

In October of 2005 Chris started working on the idea of making a much larger cradle. He wanted to design something that would be suitable for a large crowd and could offer long term reliability with regular abuse and mistreatment. Chris wanted to design and build an Industrial Sized Newton's Cradle.

An idea was born.

Though Mark had build the matched set of cradles and was properly trained and educated as a Mechanical Engineer, Chris had never built such a thing before, nor had any manner of engineering degree and was thus unencumbered by such concepts as rules and common sense when dealing with the dimensional limitations of building such a device.

What he did know from the Group's early years on Ionia St was that very high pendulums of 20 feet or more demonstrated very different effects than little ones of only a foot or so high. The physics is exactly the same, but visually the results are much more impressive. This is one particular area of physics that scales up very well.

The problem was having the balls to build it.

You see, to make a cradle on a really large scale, you have to have not only very long lines, but very large balls on the ends of them. The lines are easily done, simple plastic-coated aircraft cable is available from any hardware store (we went to Lowe's). But getting the large spherical weights that could be suitably sized, be light enough to lift but heavy enough to work well, and be tough enough to survive the impacts of a thousand collisions is a very difficult engineering problem.

The original ideas were things like large two or three foot diameter stainless steel spheres. But solid ones would be too heavy, hollow ones would dent too easily, and finding the right combination of size and wall thickness is beyond our machine shop's capabilities. Not to mention the cost of such a thing would be astronomical.

So we had to settle for something smaller and easier to obtain.

The obvious answer after much research and deliberation came to be Bowling Balls.

Thankfully Chris had been collecting bowling balls for several years already. The Group uses them as demonstrations in physics, resonance, pendulums, and suchlike as part of our Tesla Coil demonstrations. Chris had been picking them up here and there are garage sales for quite some time and had a collection of about half a dozen in the warehouse.

It was time to build a prototype and see if it would work. So on November 9 2005, as with most of our projects, we began with a trip to the hardware store and started building a simple project, we had no idea just how far this would go and that such a simple demo idea would become something that would have such far reaching effects for the Group and our students.