Match

bend it until it fits. then see what it was.

a dotted curve is already on the paper and yours is wrong -- drag the handles until the two lock together, and the graph turns out to be a marble, a kulhad of chai going cold, or a rumour running out of people

Three graphs, one at a time. Each one hides something ordinary: a marble rolling down a ramp, tea cooling in a clay cup, a message spreading through a city. You bend your own curve onto the dotted one by dragging its handles, and the equation above your hands changes as you go, because the curve has to pass through wherever you put it. When the two agree closely enough they lock, and the graph plays out as the thing it always was. The maths is ordinary school maths -- a straight line has one slope, hot things cool fastest when they are hottest, a rumour slows down when it runs out of people who have not heard it -- and none of it is asserted at you before your hands have found it.

Concepts: geometry, scaling, motion.

An interactive you play with one thumb, on Wundr.