How do you make a giant Newton's Craddle?

Factual Questions
1

Saw the Mythbusters episode and I thought they did it wrong (as they often do.) But in fairness, they were debunking a specific myth: that a set of wrecking balls suspended in alignment will behave like a NC. Now I’ll just spill out my other opinions one last time so that the discussion will stay factual:

  1. In scaling up a standard 5-ball NC (dimensions are: 1" diameter steel balls suspended from 10" long strings) you scale up linear dimensions, not mass. Let’s say you want 1-meter diameter balls suspended by 10-meter long cables.

  2. In my very rusty college physics, one must maintain the relation between the momentum of the swinging ball and the effect gravity has on its mass. Therefore, it doesn’t do to keep using steel as your medium when increasing dimensions. In Mythbusters, a symmetrical swing percentage in the high 90s was observed with the standard NC, while the percentage went down to around 60% when they used shot put-sized steel balls.

  3. So you need lighter balls as diameter increases but since your ball’s density goes down with increasing diameter, air resistance comes into play.

Therefore, your 1-meter dia spheres should be made of a light and strong material; maybe hollow spheres made of tough bonded carbon fiber, strong enough not to deform or shatter when struck by a swinging brother ball. If the set up is still too heavy, maybe fill the balls with helium or do it in a large vacuum chamber.

Will this work?

2

Where would you find a vacuum chamber large enough?

It’s been a long time since I’ve seen that episode, but ISTR that they had trouble with lighter weight balls crushing or absorbing the impact.

3

Actually as Mythbusters showed the solid part of the ball only had to be at the point of contact and distribute the load from the attach points. I’d use a solid steel rod and form the rest of the sphere out of light material like foam. The ends of the rods will contact each other as they bump. The wires should meet at the center of the rod. The sperical shape is just for looks.

ETA: vacuum and/or helium won’t make enough difference to bother.

4

There was a thread here a long time ago discussing Newton’s cradle. In particular, discussing the fact that with three or more balls, conservation of momentum and energy alone didn’t give a unique solution to the state after collision.

There was another condition that the ball material had to satisfy, something to do with the speed of sound in the material. Your hollow carbon fiber spheres may not work correctly. I’ll see if I can dig the old thread up.

5

Here’s the old thread, from twelve years ago.

6

I’m building a croquet set for Burning Man out of sledgehammers and bowling balls. Since I managed to collect 19 bowling balls, I was thinking about other projects. This got me thinking about building a giant Newton’s Cradle. Unfortunately, with the advent of the internet, it’s damn near impossible to find something that hasn’t been done before. The bowling ball Newton’s Cradle is no exception.

There’s a group called the Geek Group who built the world’s largest Newton’s Cradle. Here’s the video, although it’s super slow going. They mention that regular bowling balls won’t work very well because of the asymmetrical mass distribution in typical bowling balls (to make them behave optimally rolling down a bowling lane). I think they managed to acquire uniform density bowling balls by special ordering them which must have cost a fortune.

In any case, their giant Newton’s Cradle works pretty well, but it took a ridiculous budget to pull it off.

8

Reported.

Although I have to give these guys points for building a cool thing, spam is spam.