Phyllis Hammond & Ernst Lurker (collaboration), Four Balls in Motion
1. The purple ball at the bottom swings back and forth like a pendulum.
2. The two red balls in the center are on a horizontal stem and rotate like a gyroscope or a carousel.
3. The pink ball at the top also swings like a pendulum only in the opposite direction (an upside-down pendulum). It is anchored by a flat spring allowing the motion only in one plane.