Whiffle baseballs and rubber bands are used to create a mass-spring system with 1, 2, 3, and 4 degrees-of-freedom. Each system is driven at its resonance frequencies, and the natural modes of vibration are demonstrated. The number of masses (different discrete objects undergoing displacement from equilibrium) determines the number of natural frequencies and mode shapes. As the number of degrees-of-freedom increases, the mode shapes begin looking like the mode shapes for a vibrating string fixed at both ends. Please check out for animations of a computer model of this system.
Video was filmed at 240 fps using a Casio EX-FH20 digital camera.
Thanks to graduate student Matthew Shaw for helping setup the demonstration and for holding down the blue background in the wind for the last several clips.