A chaotic system of two connected pendulums demonstrating sensitive dependence on initial conditions. Small changes in starting positions lead to dramatically different trajectories.
The double pendulum is described by coupled differential equations:
θ₁'' = (m₂g sin θ₂ cos(θ₁-θ₂) - m₂ sin(θ₁-θ₂)(l₁θ₁'² cos(θ₁-θ₂) + l₂θ₂'²) - (m₁+m₂)g sin θ₁) / (l₁(m₁ + m₂ sin²(θ₁-θ₂)))
θ₂'' = (m₂ sin(θ₁-θ₂)(l₁θ₁'² + g cos θ₁) + (m₁+m₂)(l₁θ₁'² sin(θ₁-θ₂) - g sin θ₂)) / (l₂(m₁ + m₂ sin²(θ₁-θ₂)))
Where θ₁, θ₂ are the angles, l₁, l₂ are the lengths, and m₁, m₂ are the masses.
The double pendulum is a classic example of a chaotic system. It exhibits:
This demonstrates why long-term weather prediction is so difficult - small measurement errors compound exponentially over time.