Some Shapes

Echinus (detail) Jean Baptiste Lamarck. Tableau Encyclopédique et Méthodique des Trois Regnes de la Nature, Paris 1791-1798. Photograph by D Dunlop. |

A particle described by its wavelength $\lambda$ and orbital radius $\, R$ may be classified by shape.

Shape | Definition |

a point |
$R = \lambda = 0$ |

a line segment |
$\lambda > R = 0$ |

a plane section |
$R > \lambda = 0$ |

a plate |
$R \gg \lambda > 0$ |

a rod |
$\lambda \gg R > 0$ |

a cylinder |
$\lambda \sim R > 0$ |