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Home/Classical Mechanics/Woodpecker toy (stick–slip)

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

Friction & spring

0.42
0.28
55 N/m
μ_k cap≤ μ_s − 0.02

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.