We’ve all seen, and likely played with, a toy that has a number of steel balls hung in a line called a Newton’s cradle. When one ball is pulled and released, it causes an interesting chain reaction, where the ball opposite to it pops out then swings back, causing the same type of reaction on the original side. 19-year-old Ben Watson decided to make his own, starting with a well-rendered 3D model made in Autodesk Inventor.
As shown in the video below, his cradle setup allows the bearings to knock back and forth for quite some time. Although he initially left a tiny bit of space between bearings, he found that, “Having the balls slightly touching gave the best results… This kept the central balls from swinging which is ideal.”
For the physical build, Watson cut grooves into two pieces of ½” round stock, then bent each into a u-shape. He then set these up on a mill, and cut one side flat to act as the bottom. Holes were then drilled in this flat section for alignment pins.
The metal balls that hit each other are 1″ ball bearings. He attached a metal bead to the top of each one with JB Weld so that he could attach fishing line to them.
A piece of oak was used as the base, nicely routed and stained. He used an important technique for alignment of the pins, using two sharpened pins inserted into the metal rods to mark where the hole should be. When removed, these positions were drilled into the wood, and the actual alignment pins used to hold the cradle arms in place.
According to Watson, he’s doing this project for his physics class this semester. “I will be doing a presentation along with the model I built. I chose the Newton’s cradle because I was interested in the way it worked and why it worked the way it did,” Watson explained. Let’s hope he gets an “A!”