Segment V1.2: E-Coli Bacteria Swimming

(Related to Textbook Chapter 1 - Introduction)

Although most flow with which we are familiar are of "moderate" characteristic length, there are many extremely small-scale flows that affect our every-day life.

The flow around the extremely small E coli bacteria shown is entirely different than that around larger objects such as a swimming human. The bacteria, which are about 1 micron long and 0.1 micron in diameter, must use an entirely different method to swim than that done by humans who are about 10⁶ times bigger. Note the "spiral" wave type motion of the bacteria. Humans propel themselves through water by using their hands or feet to "throw" water backwards. This momentum exchange principle does not work at the extremely small scale of the bacteria.