Motion shows where an element came from and belongs

What it is

A new surface that pops in at screen centre does not say which tap produced it. Growing a panel out of the tapped button, or flying a thumbnail into a cart, draws “who caused whom.” That is motion answering origin and belonging with a trajectory — a common-fate spatial bind — not yanking attention to a flash.

The same displacement may emit a transient as a side effect. The claim here is different: after the path, the viewer can point at the source and know where to look to put the surface back.

Why it happens

People encode objects as source–path–goal. A surface that expands from control A is filed as an extension of A, not as an ownerless layer. Common fate does the grouping: things that grow from one place or collapse back into it are seen as one set.

Without a path, belonging falls back to static proximity or memory. When the button is top-left and the panel is centred, proximity is weak and memory drops across a navigation. The trajectory is a short-lived spatial index: it draws the causal link in a few hundred milliseconds, then can vanish.

This is not the same as keeping one object’s identity across two screens. The new surface is often a different object that still needs to declare which host it hangs from.

Studying it

Treat path versus no path as the manipulation: the same trigger–surface pair, expanding from the trigger in one condition, fading in at a fixed location in the other.

Dependent measures: whether people can later name the trigger, whether return taps hit the original control, erroneous dismissals. Eye tracking asks whether gaze follows from trigger to surface during the expansion. Classic common-fate displays group synchronously moving items; transition studies ask whether the expansion source gets bound.

In the lab the trigger is often conspicuous; in products it may be a small toolbar icon, so binding failures are more common.

Where it stops holding

• If the trigger has left the screen (scrolled away, page already changed), the path points at empty space and the cue fails.
• Nearby candidate sources can steal the bind.
• A full-screen modal is not owned by a button; flying it out of a corner fabricates belonging.
• Once an origin story is told, the next screen should not retell it on an unrelated axis, or the two spatial stories collide.

Applying it

• Menus, cards and lightweight sheets opened from a control should expand from and collapse into that control, not slide in from a shared screen edge.
• For “object changes container” actions (favourite, move to folder), send the object along a path into the target.
• Check: interrupt the transition and ask where the panel came from. If the trigger cannot be named, the path did not encode belonging.

Related

• Same group: F7.01.1 Motion draws attention to where change happened · F7.01.3 Motion fills a wait and changes how long it feels · F7.01.4 Motion that does none of those jobs is pure cost
• Nearby: F7.07 Motion expressing spatial relations · F7.04 Shared-element transitions · A2.05 Common fate
• Search terms: origin and belonging · common fate · source path goal