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  • Visitors interact with the Coupled Pendulums exhibit.
  • Exploratorium founder Frank Oppenheimer with an early version of the Coupled Pendulums exhibit.
  • Visitors interact with the Coupled Pendulums exhibit.
  • Exploratorium founder Frank Oppenheimer with an early version of the Coupled Pendulums exhibit.

Coupled Pendulums

Linked pendulums can get one another going.

Start one of these two pendulums swinging and soon you’ll see the other pendulum start swinging, too. Keep watching and you’ll see the two pendulums take turns, alternately swinging energetically and coming to a near standstill.


Where:   Crossroads: Getting Started
Exhibit Developer:   Exploratorium Founder Frank Oppenheimer, 1981

What’s going on?

Everything vibrates at its own unique rate, or frequency. Bridges, atoms, and playground swings—each wiggles, waves, or swings with a characteristic natural frequency.

In this exhibit, two pendulums are joined together, and there are two natural frequencies. In any system consisting of similar parts joined together—like atoms in a molecule or girders in a bridge—there are as many natural frequencies as there are parts.

Energy added to one pendulum moves back and forth between both pendulums. This happens three times a minute, which is the difference between the two natural frequencies, 47 and 50 swings per minute.

 

Going further

The unfinished aesthetic of this exhibit reflects Exploratorium founder Frank Oppenheimer’s openness to tinkering with exhibit design. Made from hardware store parts and a staff member’s kitchen table, this exhibit went through many stages before it premiered on the museum’s exhibit floor in the early ’80s.

Since then, there’ve been more alterations and iterations, including removal of a motor and an anonymous addition of whimsical feet. The Exploratorium has generated a smaller do-it-yourself version of this exhibit and a full-sized swing-set of coupled pendulums. (click image to enlarge)

 
Phenomena: Energy: Conservation of Energy, Energy: Kinetic, Energy: Potential, Motion: Composition of Perpendicular Motion, Motion: Pendular Motion, Motion: Periodic Motion, Motion: Simple Harmonic Motion, Natural Frequency, Resonance, Rhythm
Keywords: pendulums
Aliases: Coupled Resonant Pendula, Coupled Resonant Pendulums, Stop and Start

More to explore

Science activity that demonstrates resonance in a pendulum
Coupled Resonant Pendulums

Two pendulums influence each other’s motion to create Intriguing patterns.

Palace of Delights
Produced for NOVA in 1982, Jon Else's film looks behind the scenes at the Exploratorium.

Related exhibits

Sand Graph
Sand Graph

Sand traces a pendulum‘s motion.

Chaotic Pendulum
Chaotic Pendulum

When you set these pendulums swinging, the motion of each one affects the others.

Pendulum Snake
Pendulum Snake

These balls dance in changing patterns as they swing to their own rhythms.


IMLS acknowledgment

This web project was made possible in part by the Institute of Museum and Library Services [MA-30-16-0175-16].

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