Woodpecker toy (stick–slip)
The woodpecker toy hops down a rod by alternating static friction (stick) and sliding bursts (slip) as internal springs and gravity load the sleeve. This page implements a compact phase machine with breakaway based on static friction and motion damped by kinetic friction — enough to show the rhythm, not enough to reproduce every experimental trace from tribology papers.
Who it's for: Stick-slip friction demos and nonlinear dynamics outreach.
Key terms
- Stick-slip
- Static friction
- Kinetic friction
- Woodpecker toy
- Phase model
How it works
A sleeve with dry friction on a rod alternately locks under static friction while an internal spring loads, then slips when the breakaway condition is exceeded — a cartoon of the woodpecker’s hopping cycle, not a detailed multibody model.
Frequently asked questions
- Why clamp μ_k below μ_s?
- Physically kinetic friction is typically slightly less than static; the UI enforces a small margin so breakaway remains meaningful.
- Where is the toothed rod geometry?
- Omitted. Real toys use directional catches; here a spring-load accumulator stands in for asymmetric catches.
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