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ELI5 Yahaaa

Two matching halves

What Is Symmetry?

A shape is symmetrical if you can fold or turn it and it lands on itself.

Symmetrical Fold it and the halvesmatchNot symmetrical The halves do not lineup
The test is a fold, not a feeling.

  1. Step 1 of 5

    The fold test.

    1 Draw a line2 Fold along it3=Do the halvesmatch?

    Draw a line through a shape and imagine folding along it. If the two halves land exactly on each other, that line is a line of symmetry.

  2. Step 2 of 5

    Some shapes have many lines.

    Circleinfinitely manySquare4 linesRectangle2 lines

    A rectangle has two. A square has four. A circle has infinitely many, because any line through the centre works.

  3. Step 3 of 5

    Turning symmetry is different.

    Fold symmetry Matches when flippedTurn symmetry Matches when rotated

    Some shapes look the same after a rotation but fail the fold test. A three-bladed fan looks identical every third of a turn.

  4. Step 4 of 5

    Living things are symmetrical for a reason.

    1 Matching wings2 Matching limbs3 Petals around acentre

    Animals that move forward have a left and a right that mirror each other. Two eyes, two ears, matching legs — it makes movement balanced.

  5. Step 5 of 5

    Perfect symmetry is rare.

    A real face Nearly symmetricalA mirrored half Perfectly symmetrical —and unsettling

    Faces are almost symmetrical, never exactly. Photos that mirror one half of a face look eerie, because we are used to the small differences.

    Snowflakes have six-fold symmetry because water molecules link at 120-degree angles.

The short version

Symmetry means a shape lands on itself when folded or turned — and it is easier to test than to eyeball.

Try it yourself

Fold a paper in half, cut a shape through both layers, and open it. You have made a symmetrical shape by force.

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