Wilberforce Pendulum

Consists of a stand consisting of a pair of inverted V-shapes, joined at the top by a bar and by a plate at the bottom. From the top bar hangs a large-diameter spring. The end of this spring is attached to the center of a heavy metal bar, which has adjustable weights at various locations so that it's center of mass be adjusted to line up with the spring.

To demonstrate the action of an unusual oscillator, which transitions between two modes: oscillator which exchanges energy between elastic potential energy and kinetic energy, and an oscillator which exchanges energy between elastic potential energy (but twisting the spring this time) and rotational kinetic energy.

Essentially, it can be thought of as oscillating between these two modes; between twisting and moving up and down.

• Wilberforce spring

Pull the spring down until it's about to hit the bottom of the apparatus, and release it. You should then see it gradually move from purely up-and-down motion to twisting motion, and back.