Where does tumbling collide?

In sedimentary geology, tumbling describes how rock fragments carried by a river or surf are rounded and smoothed as they roll and collide, so that angular clasts gradually lose their edges and acquire a polished, rounded form. Kuenen's 1956 Experimental abrasion of pebbles: 2. Rolling by current in The Journal of Geology measured this wear in a circular flume and tied rounding rate to grain size, hardness, and transport distance. The referent is the progressive loss of mass and angularity of a clast under repeated impacts, read as a roundness and surface-texture record of transport history. It is the natural counterpart of the engineered barrel that finishes metal parts, and unrelated to a swimming bacterium's tumble.[1]

Unit

The roundness and mass loss of a clast as a function of transport distance

Recovery means

Not applicable

Measured by

Quantified by roundness indices, mass-loss rate, and surface texture against transport distance in flume or field studies

In microbiology, tumbling is one half of how a flagellated bacterium such as Escherichia coli moves: it alternates smooth straight 'runs' with brief chaotic 'tumbles' that randomly reorient the cell, and by lengthening runs when conditions improve it performs a biased random walk toward attractants. Berg and Brown's 1972 Chemotaxis in Escherichia coli analysed by three-dimensional tracking in Nature established the run-and-tumble pattern by tracking individual cells. The referent is a reorientation event in a swimming trajectory, caused by flagellar motors reversing, measured by tumble frequency and run length, and it has nothing mechanically in common with pebbles abrading or parts in a barrel beyond the shared word.[2]

Unit

The tumble frequency and run length of a swimming cell's trajectory

Recovery means

Not applicable

Measured by

Measured by three-dimensional cell tracking giving tumble frequency, run length, and reorientation angle