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Chaos and Predictability

25 February 1989

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Why is the trajectory of a ball easier to predict than the weather? What are the barriers to predictability? Newton's laws say that if you know enough about a system at one time you can predict the state at later times. How much is enough? We will see that for many systems you cannot know enough to make reliable predictions beyond relatively short times. This phenomenon is known as `chaos`. Examples will be discussed involving simple mechanical objects, fluid flow, the weather, and an equation that a high-school student can solve using a hand calculator or a personal computer.