Static vs Kinetic Friction Incline Lab (2D)

Incline & Block

Incline angle θ 15°

Block mass (m) 2.0 kg

Friction Coefficients

Static μₛ 0.50

Kinetic μₖ 0.35

Surface preset

Live Readout

Critical angle θc

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State

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Normal force N

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Weight component mg·sinθ

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Friction force

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Acceleration a

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How it works

A block of mass m sits on a ramp tilted at angle θ. Gravity's component along the slope is mg·sinθ; the component pressing into the surface is the normal force N = mg·cosθ. While the block is still, static friction self-adjusts to cancel the along-slope pull, up to a maximum of μₛ·N. That maximum is reached exactly when:

mg·sinθ = μₛ·mg·cosθ
tanθ = μₛ  →  θc = arctan(μₛ)

Below θc the block is locked in place — static friction adjusts to match the driving force exactly. The instant θ exceeds θc (or μₛ is lowered past tanθ), the block breaks free and kinetic friction — usually smaller than the static maximum — takes over, giving a constant acceleration down the slope:

a = g(sinθ − μₖ·cosθ)

Because both terms are mass-independent, the acceleration once sliding does not depend on the block's mass — only the force magnitudes (N, friction, weight) scale with m. The mass slider changes those forces without changing how fast the block accelerates, a genuine and often counter-intuitive consequence of Amontons–Coulomb friction.

Auto-sweep angle — slowly raises θ from 0° so you can watch the block sit motionless, then suddenly break away right at θc.
Force diagram — live vectors for gravity (white), normal force (cyan) and friction (red/green).

Gravity (mg) Normal force (N) Friction (static) Friction (kinetic)