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Slope and snow
Flow resistance
mu is dry Coulomb friction; xi is the Voellmy turbulent coefficient (smaller xi = more drag).
Model checks
The science
Voellmy-Salm flow law
A grain of the flow obeys dv/dt = g sinθ − μ g cosθ − g v² / (ξ h), where θ is the local slope, μ the Coulomb friction coefficient, ξ the turbulent friction coefficient (m/s²) and h the flow depth. On a constant slope the speed approaches v∞ = √(ξ h (sinθ − μ cosθ)) and follows v = v∞ tanh(t √(A k)) with A = g(sinθ − μ cosθ) and k = g/(ξ h).
Angle of repose and runout
Nothing moves when tanθ ≤ μ. On the flat outrun friction alone stops a sliding mass after d = v² / (2 μ g); drag shortens it further, which is why the runout curve rises steeply with the start angle.
Honest simplifications: a one-dimensional track, constant flow depth, no entrainment of new snow, no lateral spreading, no powder-cloud air dynamics, centripetal pressure in the curve ignored. The grains carry slightly different friction (±10%) so the slide spreads out. Educational physics only.
What to try
- Choose Gentle 30: the push is near zero and the snow barely moves.
- Choose Powder cloud: low friction and weak drag give very high speeds.
- Raise mu above tan(slope) to see the slope stay stable.