Gallery 2

Angry Arms

Chaos theory is predictably unpredictable!

How it works

Spin the connected pendulums and watch how the arms move in unpredictable patterns. Even if you try to start from exactly the same position, the final pendulum pattern will vary greatly.

Things to try or ask around the exhibit

  • Try to make all of the arms swing the same way, such as all clockwise.
  • You're trying to control how the exhibit works, so why do the arms swing so unpredictably?
  • Does the unpredictably of the swinging arms relate to something such as making weather forecasts? Is it surprising that weather forecasters get it right so often?


The arms swing around due to energy, gravity, mass, centripetal force and friction, but when you try to make the arms swing the same way, slight adjustments to your wrist angle, turning force, each arm's position and even temperature and turbulence inside the exhibit can affect how the 'Angry Arms' will swing around. This is because the arms swing in unpredictable patterns that are influenced by very small, sometimes imperceptible changes so they behave in chaotic patterns.

Chaotic systems appear to be random, but they are actually built upon patterns that can be studied mathematically as chaos theory. However, as complex systems develop, they are highly sensitive to slight changes in conditions, so that small events can generate powerful consequences. Scientist Edward Lorenz once proposed the butterfly effect: "Does the flap of a butterly's wings in Brazil set off a tornado in Texas?". This was an elegant way of proposing that small effects can amplify into very large effects as seen within chaotic systems.

Chaotic systems are very sensitive to starting conditions and a chaotic system’s outcome is very hard to predict, especially over a long period of time when so many factors influence the system.

Finding the science in your world

Many natural phenomena are chaotic, including the weather and a human heartbeat that starts to beat out of control. The study of chaos can also be applied to complex human systems such as the stock market.

Meteorologists must deal with unpredictability of natural systems when they make weather forecasts. Even small changes in today's weather can affect natural systems to create unpredictable weather events in a few days or a week's time. When weather predictions don’t always match up to what happens in real life, you can blame the unpredictability of chaos!

When the human heart begins to beat out of control such as in a heart attack, this is called fibrillation of the heart muscle. The heart stops beating regularly and instead goes into an unpredictable chaotic pattern of beats. Researchers are examining a new system where smaller signals are sent into the victim’s heart. These take advantage of the patterns in the chaotic heart beat to bring the heart back under control.