This “frog” is an excellent building/crafting activity for kids. It takes less than 15 minutes to build and will have your kids playing with it all day! (credit: Lubię majsterkować, by Adam Słodowy). The cool behaviour is due to inertia and the rolling of the ball inside of the contraption.
Here’s how to do it:
1. Take a piece of paper and cut out the following figure. The dotted lines are where you fold. Make sure you make the main strip at least the width of a marble or ball you will be using. The ball should have a lot of room to roll inside.
2. Fold along the dotted lines. Glue the tabs as shown below. Before you glue the last piece, put in a heavy marble or ball inside. Wait for the glue to dry.
That’s it! The contraption is done. You can test it out on any slanted surface / ramp. Try different sizes, different types of paper, different mass of ball.
If you want to make it an experiment, you can change one variable (mass of ball, material, size, etc.) and observe how the contraption behaves as a result. You can build several and have races between them. Have fun!