The swipe-versus-pan velocity cut decides a jump or a follow

What it is

The same travel is read two ways at lift-off speed: above a velocity threshold it is a swipe (a discrete jump to the next page or card), below it is a pan (content stays where the finger left it). The cut chooses a command type, not the initial speed of inertia—inertia is added after a pan is already chosen. Pagers, stories, and carousels all sit on this knife.

Why it happens

Pan is position control: output tracks the contact, and on lift the position should remain. Swipe is pulse control: output is “one step that way,” and content need not stop on the pixel the finger left. The classifier looks at velocity in a short window before lift (sometimes also heading stability). Too low, and a slow follow becomes a page turn, the card slipping out from under the finger; too high, and an intended flick is a failed drag, so people try again. It is orthogonal to direction lock: lock the axis first, then measure speed on that axis.

Studying it

Have people “leave the card halfway” (pan intent) and “fling to the next” (swipe intent) while sweeping the lift-off speed cut. Measures include intent–label match and extra repair gestures. Record real lift-off speeds; do not use the developer’s own flick as the threshold. Page animations can hide misclassification—it “still got to the next page” when the user meant to stop in between.

Where it stops holding

A continuous reader with no pages often folds swipe into inertial scroll, and the threshold degrades to “whether to impart initial velocity.” Drawing strokes must not be promoted to page turns by speed. System back gestures also use velocity, but the semantics are navigation, not paging. This leaf only splits swipe/pan; it does not convert the number across screen sizes.

Applying it

• State for a pager: commit one step only if lift-off speed ≥ the threshold; otherwise snap back to the current position.
• Keep the tracking phase as pan; do not turn the page on instantaneous speed before lift.
• Script “stop between pages” and “fling to next” and count wrong turns versus flings that do not take.

Related

• Same group: C3.29.2 Velocity must be judged together with distance · C3.29.3 Near the cut, the same stroke flickers between two readings · C3.29.4 Velocity thresholds must be recalibrated across size and resolution
• Adjacent: C3.05 Swipe · C3.07 Pan
• Search: swipe threshold · pan versus flick · lift-off velocity