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Sandbox Physics
Geometric elasticity · A course with experiments

FROM A BUCKLED STRIP TO A FOLDED TUBE

Geometric elasticity: how thin things bend, buckle and snap

A thin sheet can bend for almost nothing, but stretching it costs far more. That one fact explains why a clamped strip buckles into an arch, why the arch jumps when pushed, why a growing disc curls into a dome and why a folded paper tube can click into a second shape and stay there. Each chapter derives one of these and checks it in a Lab.

A strip between two clamps · Chapters 1–4

Bend, buckle, snap

Find out why thin things bend instead of stretching, buckle a clamped strip into an arch, push the arch until it jumps, then work out how fast the jump grows and how the strip rings afterwards.

Start with a thin strip →

Shape from geometry · Chapters 5–8

Growing discs and folded tubes

Give a disc lengths that no flat sheet can hold and find the thickness where it gives up and curves, fold a Kresling tube that clicks into a second shape, then read the snapping-beam paper figure by figure.

Start with a growing disc →

Eight chapters, with examples and experiments

  1. 01 L1

    Why a thin sheet bends instead of stretching

    Why does a sheet of paper bend at a touch but hardly stretch at all?

    Read and try →
  2. 02 L2

    A clamped strip buckles into an arch at the Euler load

    How far must the ends of a clamped strip be pushed together before it buckles, and how high does the arch then rise?

    Read and try →
  3. 03 L2

    Pushing an arch until it snaps

    When a blade pushes a buckled strip slowly down, where does the strip jump, and why there?

    Read and try →
  4. 04 L3

    How fast a snap happens

    Once the blade lets go, how long does the strip take to snap, and what sets that time?

    Read and try →
  5. 05 L2

    Growth that no flat sheet can hold

    What does it mean for growth to give a sheet a curved geometry, and why can no flat sheet have it?

    Read and try →
  6. 06 L3

    The thickness where a disc buckles

    A disc is asked for a curved geometry. Below what thickness does it leave the plane, and how does its energy split once it has?

    Read and try →
  7. 07 L3

    Kresling folds and their stress-free shapes

    Why does a twisted origami tube stay folded with nothing latching it, and which designs spring back instead?

    Read and try →
  8. 08 L4

    Reading the snapping-beams paper

    What does each figure of Pandey et al. (2014) show, how was it obtained, and which of its numbers can a reader check?

    Read and try →
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