Nov 12

Newton’s Cradle big or bouncy

Jeanette planningbouncy with plans 2 bouncyJeanette designed and built a bouncy Newton’s Cradle.  She stapled dental floss to glow-in-the-dark bouncy balls and suspended five of them from a framework of skewers, coffee stirrers, and a paper towel tube.  Alignment of floss and stability of frame prevented the ideal bouncing of balls, we suspect. Click on the photo on the right to watch a short video showing the frame rocking and all the balls start moving together shortly after a promising first couple swings.  It was impressive how quickly she constructed this.

We all continued work on our giant Newton’s Cradle.  With bowling balls drilled last time, we constructed a saw horse, underneath which to hang them.  A photo shows Myles cutting one saw horse leg to length.  We discussed connection options from the balls and paracord to the horse: drill holes through the top beam of the horse or cut open a bicycle inner tube and lay this across the top beam so that the paracord does not shift.  Holes would commit us to certain ball spacing, but that spacing is crucial for long-lasting action (many impacts of balls), so a hybrid approach would be to start with just the rubber topper and, once we are confident we can position the bowling balls to very nearly touch each other (this is the ideal), use nails or staples to secure the paracord to the rubber covered saw horse.  We will also need guide-ropes, like at the ends of a tent, to prevent the saw horse from swaying lengthwise.

cutting leg for bigWe played a “Black Bag” game to illustrate what it’s like to infer structure that we cannot directly see: replicating Lego structures hidden inside black plastic bags that allow touch, but not sight.  The colors of the Lego bricks inside the bags are not possible to determine, but students found two approaches to determine which size bricks comprise the structure: (1) feeling with a fingernail for joints between bricks or (2) breaking one brick at a time off the structure, feeling its dimensions, and replacing it (both techniques worked through the plastic bag).  Our inability to replicate color is analogous to qualities that our best instrumentation of the day cannot determine.  There is always something unseen, always something further to characterize.

Although the activity is most pure when we do not open the bags, because in scientific exploration we infer structure when there is no bag to open, we could not resist.  Before opening the bags, though, we compared all the students’ replications and found one inconsistency.  We went back to the bags to see if 1 student was inaccurate, all but one student was inaccurate, or the bags contained different structures.  We found that 1 student had created a mirror image of the model and corrected it before opening the bags.  This reflects what scientists do when they compare their experimental results to those of others.

Finally, we discussed atomic structure, one reason that atoms are special (indestructible by chemical means), and radioactivity.  Each student summarized a page from the Encyclopedia of Science and walked us through it.

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