050/366: Physics Toy

When we were in DC back in July, SteelyKid purchased a toy Newton's cradle. And I already owned a 1000fps video camera, so it was inevitable that the one would end up in front of the other...

I spent a while this afternoon making high-speed video of the toy clicking back and forth, but didn't have time to write up the analysis. And I'm leaving wayyy too early this morning to fly to California for a few days (giving a couple of talks in Sacramento, then visiting my sister for a bit), so you'll have to settle for this teaser image for now:

SteelyKid's toy Newton's cradle in mid-swing. SteelyKid's toy Newton's cradle in mid-swing.

Well, OK, here's the video, too:

But you'll have to wait to see the detailed analysis, and that's that.

I am not 100% certain I'll get time to edit and post photos while I'm on the road, but I'm taking my DSLR with me, and if I can't post while I'm there, I'll catch up when I get back next week.

More like this

A little while back, I used a photo of SteelyKid's toy Newton's cradle as the photo of the day, with a bonus video: I mentioned that I was going to do some analysis of this at some point, but didn't have time right then. I had a bit of time to poke at this yesterday, though, so here's some physics…
SteelyKid is spending a couple of days this week at "Nerf Camp" at the school where she does taekwondo. This basically consists of a bunch of hyped-up kids in a big room doing martial activities-- taekwondo class, board breaking, and "Nerf war" where they build an obstacle course and then shoot…
It's been over a month since I did a photo-a-day post, largely because I haven't been taking many pictures for a variety of reasons. I do still mean to get a year's worth of good photos done, but the "daily" part has completely disintegrated at this point. As a way of getting somewhat back on…
I got a new camera for Christmas, not because there's anything wrong with my DSLR, but because I wanted something that could do high-speed video. So I now have a Casio point-and-shoot camera that will record up to 1000 frames per second, woo-hoo! To break it in, I got the kids to help out by re-…

Since I worked with Newton's Cradles for my grad school work, two things you should definitely know for your analysis:
1. Don't try and model the sphere contact like springs. The force grows like $F = kx^{3/2}$, and so is completely nonlinearizable around 0 (barely touching). If you know any folks in MechE, they can probably tell you about the Hertz contact law, and I've seen surprisingly many people who do work on this thing (granular dynamics) not know about this.
2. One ball in at V_0 does not equate to one ball out at V_0. It always spalls, which is why the system settles down to everything moving in sync by the end. You can pretty clearly see the spalling in your video, and can confirm this to yourself by integrating the equations of motion (with the Hertz law) on a computer.