Newton made a device that shows the conservation of momentum and energy using spheres. You can lift the end spheres and let them go, creating a chain reaction on the opposing side.
Step 1: The Supplies
You will first need to get wood, nails, hammer, fishing string, bouncy balls, and staples.
Step 2: The Pieces
You need to make four legs depending on the size you want your cradle. Then you need to make 4 pieces that you will put on top of the cradle. The sides being longer than the end pieces.
Step 3: Assembly
You want to take your four legs and attach the tops with nails. Follow the assembly you want to take your spherical objects or rubber balls in my case and drill a hole straight through it. Then you want to take one of your nails and tie your fishing string to the flattened end, which makes it easier to get the sting through the hole you previously drilled.
Step 4: The Hanging
In this step you want to take your wooden stand and hang the spheres to it. You want to take each side of the fishing string and wrap it around the top of the stand and stapler he string down. You want to make sure that every sphere is positioned at the same height so they all bounce correctly.
Step 5: The End
Now that your spheres are all hung at the same heights you should be able to pick up one or two of them and with a simple drop, you can see the energy transfer to the opposite side while the ones in the middle stay stationary.