Newton's Cradle Help

Jul 2018

When I was a kid, a relative had a Newton's Cradle that worked perfectly. The balls in the middle DID NOT MOVE! I purchased a toy Newton's Cradle but, needless to say, it does not work well.

I decided to make my own. Since I am a woodworker, I wanted to make a nice one out of exotic woods. However, although I thought I measured carefully, I had some problems. I bought some steel balls at a thrift shop and measured them at 1". I built the NC with holes drilled in the transverse arches (see attachement) at exactly 1". However, the balls are actually 1⅛". Not my fault—I was using a bad ruler. LOL Who makes steel balls at one and an eighth inch, anyway?!

I digress. What I would like to know is 1) is it necessary to secure 1" steel balls? ...and 2) how perfectly do the balls need to be lined up for efficient kinetic performance? ...and 3) does the fact that the transverse supports are arched impact the kinetic performance?



Apr 2017
Nice carpentry , robotarmy ....

does the fact that the transverse supports are arched impact the kinetic performance?!
Yes ... that's the first thing I noticed ... I guess you need all the balls aligned in a straight horizontal line for this to work well ... if so the strings will be different lengths for each ball which will make the swing time of each slightly different.

I would think perfect alignment is essential.

I can't imagine the size of the balls is too important , as long as they're the same ... but how will you connect the string ??? not easy to drill a hole ! Super glue??

This is a very challenging project , it seems deceptively simple to make one of these , but if everything is not perfect it won't work ..

You're entering unknown territory with different string lengths ...

Still push on with your experiments , you may discover an interesting variant on the standard model...

The one in this video is pretty useless , they used bowling balls , too soft a material so little energy is transferred on impact and it quickly comes to stop ... with steel balls that size it should continue swinging for minutes ...

Last edited:
Jul 2018
Thanks oz93666,

Wasn't sure if this would be responded to as I guess most posters are actually physics students. The closest I get to physics is watching The Big Bang Theory! LOL

I saw that video! I think that's the one in which they stand around talking for 30 min, but never operate the NC.

I guess I thought I could get away with the arches because I saw a retail NC with arches (see attached). I guess just cause it's for sale doesn't mean it works well.

The balls have a dab of epoxy with a hole through—holds pretty well. I plan to construct a jig to hold the balls in place (see attached). The fishing line goes through a tiny hole on one side of the transverse. I then have wee ebony pins for the larger holes on the other side to secure the line. I should be able to get the balls perfectly aligned.

My concern is do they need to hang at a 90° angle to work? In the attached illustration, as per the red lines, the size of the balls do not line up with the holes as was the original plan. I can get 10-1" steel balls for $15, but don't want to bother if a physicist said "No dude, it won't matter," as it were.