This was the first Hackathon I have ever competed in, so I made something simple. I made a Newton's Cradle with what I had on hand. The purpose behind making this was that I knew it would be decently easy to create as this was my first time and I only had approximately four hours to create it. The purpose is purely so I can have my own Newton's Cradle.

What you need:

Wood
Band Saw
Sand Paper
Wood Glue or Brad Nail Gun
Drill
Sewing String or Embroidery Floss
Tape (I was short for time and needed a simple way to secure the metal balls on the string.)
At least 5 Metal Balls
Ruler
Scissors

Step 1: Step 1: Cutting the Wood and Securing It

First, I used a band saw and some scrap wood to cut pieced of wood that were 20cm x 3cm with a width of about 1 1/2cm each. I measured them out prior to cutting with a ruler and marked off with a pencil. I made 10 equally sized pieces. (I also sanded them down a little because they needed to be smoothed out.)

Next, I secured the wood pieces together with a brad nail gun to make a frame. I started by making a two squares and connected them at the top with the last two pieces and some brads.

Step 2: Step 2: Drilling Holes Pulling Thread Through

Next, I drilled holes in the top two pieces of wood. They were about a centimeter apart because the metal balls that I had to use were kind of small. I cut pieces of string at decently long lengths so I could make them hang equally one I got them all through the holes I drilled.

Step 3: Step 3: Securing the Strings and Hanging the Metal Balls

Next, I taped them so the strings were hanging equally so the balls would line up. Then, I cut small pieces of tape and hung the balls on the string with the tape. (Keep in mind, it is not that sturdy, but it was a quick solution.) Make sure the tape is not in the way of where the metal balls will make contact with each other otherwise the desired effect will not occur.

Finally, I tested the by swinging one of the metal balls to see if the ball would produce an equal amount of force on the other side.