Inertial scrolling is too unpredictable for precise positioning
Aliases: coast imprecision · fling error · inertial scatter
What it is
A deceleration curve can land the same effort in the same band, but a band is not a row or a tick. Precise positioning—item 47 under the hairline, a timeline on a particular second, a map on a particular street—cannot ride inertia. Inertia is for browsing. Alignment still belongs to tracked panning or a tick-bearing drag.
Why it happens
Initial-velocity estimates are noisy and so is the arm’s peak on each throw; multiplied, stop-location standard deviation often spans several rows or a whole screen. Expectation holds only coarsely: harder travels farther, lighter dies sooner. The longer the flight without a visual closed loop, the more error integrates. Snapping to detents can hide some error by quantizing a continuous stop; that is not better aim. If the detent is not the target, snap pulls people off the place they meant. Binding select, purchase, or crop to a coasting stop hands commit to noise.
Studying it
Name a target (“put 47 just under the top bar”), allow one fling and no mid-coast brake, and measure final error. Then allow a tracked correction as a control. Independent variables include list density, whether detents snap, and target distance. Error growing with distance is direct evidence that inertia is the wrong precision tool. Subjective “I landed pretty close” often comes from a large target; switch the task to thin rows or timeline ticks and the rating drops.
Where it stops holding
A song wheel or a ticking time picker uses inertia on strong detents: inertia turns many ticks, snap supplies precision, and the split is explicit. A game fling for skill direction wants a sector, not a pixel. On a short list that never fills a screen, inertia barely appears and this limit does not apply.
Applying it
- Browse long streams with flings. Align, compare, and commit with tracking or step buttons. Do not make a coasting stop the only way to arrive.
- When landing on ticks, enable snap in the low-speed band, and let a still-down finger fight the snap for a fine adjust.
- Write the task as “stop this row under this line,” first with one fling only, then with tracking allowed. If one-fling error often exceeds two rows, the task cannot be finished by inertia.