If you are unfamiliar with this device the photo will help you! The device has five hanging balls that demonstrate Newton’s Third Law of Motion. “For every action, there is an equal and opposite reaction.”

The fascination with this device is the way that it works. If you pull up one ball on one side and release it, then one will fly out on the other side. This will continue until the device slows and stops.

Step 1: Build the frame. We used hot glue and low-temperature glue guns. I only use this challenge with 5th graders and they follow strict safety rules.   TIP: Keep extra craft sticks close by to use to hold items in position instead of using fingers!

Step 2: Add the strings. This turned out to be very tedious and full of problem-solving opportunities.  The strings must be the same length and spaced apart perfectly. Above you can see one student holding the strings in place while the other applies glue.

Tip: Test often! After adding two strings with attached marbles, we tested to make sure those two would clack together well. If they were too far apart, the kids took it apart and re-did the gluing.

The one above looks great! But… do you see the problem? The marbles are too far apart. They will not hit together the way they should. The correct position is with the marbles actually touching.

We encountered several different things with the strings that would create a problem that had to be solved.

The device in this photo looks great. But, it did not work well at all. Can you see the problem?

The strings are too short! When you pull back one marble to release it, the shortened string does not provide enough impact to make the other marbles react. The strings should almost reach the bottom of the device in order to work best.

TIP: I have a Newton’s Cradle that I purchased and I allow kids to see it as they work on their creations. They need to note that the strings are long enough to almost touch the tabletop and the metal balls touch one another when hanging.

TIP: The frame needs to be squared. This simply means the lengths of the sides and the ends must be the same. If one side is longer or angled a little differently, then the marbles don’t follow a path that produces the result you want.

TIP: We used beads or straws glued or taped to our marbles as a way to attach the strings to the marbles. This works, but they do pop off easily.

We learned to place a spot of glue on the marble and let it dry a little before laying the bead or straw on top of it.

Students used forceps to handle the beads and straws.

TIP: Do you see the clever way this team threaded the string through the beads. They did this because the marbles will slide along the string and get out of alignment.

This keeps them from clacking together consistently. We solved this problem in 2 ways. We added a drop of glue inside the bead or threaded the strings with a loop.