ALT A cartoon depicts a one-dimensional cell train of epithelial tissue — a long, horizontally-oriented pink blob. At the left end of the cell train is a blue circle with a black, double-ended arrow and the Greek symbol ω above it, representing a collagen coated glass bead that applies force. Within the cell train are four sets of black waveforms with three black ovals between them that represent cell vertices, labeled i-1, i, and i 1. Above the two waveforms between the ovals is the letter k, representing cell stiffness, and the letter li with a double ended arrow, representing the cell length. Below each oval is an arm that forms right angles, with the Greek letter 𝜁 denoting friction, leading to three ground symbols: downward facing triangles made of horizontal lines that decrease in length.