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Mouse Scroll Inertia Test

This mouse scroll inertia test measures the burst after one flick. Give the wheel a single flick inside the box and take your finger off. It reports how many events arrived, the peak delta and how long the momentum lasted.

Flick area

One flick, then hands off

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last burst duration

Delta per event during the last burst

Flick the wheel once and let it spin down.

Burst statistics

Events in burst
0
Peak delta
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Longest burst
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Live mouse

Measure inertia cleanly

  1. 1. Flick once

    A single sharp flick, then lift your finger. Repeated flicks merge into one burst.

  2. 2. Watch the curve

    A free-spin wheel shows a long decaying tail; a ratchet wheel stops abruptly.

  3. 3. Compare modes

    Toggle your wheel's ratchet/free-spin button and flick again.

What inertia tells you

Free-spin detection

Bursts over 600 ms almost always mean a free-spinning wheel or trackpad momentum.

Decay curve

The sparkline shows how smoothly the momentum tapers.

Peak delta

How hard the first events hit, useful for tuning scroll speed.

Mode comparison

Measure before and after changing settings.

Inertia terms

Free spin
A wheel mode with no detents that keeps spinning after a flick.
Momentum scrolling
Software inertia on trackpads that continues scrolling after fingers lift.
Burst
A run of scroll events with gaps under 180 ms.
Decay
The way delta sizes shrink as the spin slows.

Inertia questions

My ratchet wheel shows 300 ms bursts. Why?

A fast flick produces several notches in quick succession. That is normal; the tail is what matters.

Can I turn off trackpad momentum?

macOS: System Settings → Accessibility → Pointer Control → Trackpad Options. Windows: it depends on the touchpad driver.

Why does Chrome show different numbers to Safari?

Browsers synthesise momentum events differently. Compare within one browser.

Fix scroll momentum issues

Scrolls far past where you wanted

Disable momentum or switch the wheel to ratchet mode.

Momentum stops abruptly

Normal on some drivers; not a fault.

No events at all

Keep the cursor in the box while flicking.