From the department of amazing facts

Notes [1] today:

• The flagellar motors in a bacterium such as Escherichia Coli rotate at up to 18,000 revolutions per minutes. Each rotation is powered by the flow of about 1,000 hydrogen ions across the inner membrane. The motor can turn the flagellum in either direction, clockwise or anticlockwise, on demand. 
  
• E coli cells push their way through water about at 30μm/s -- that is, 10 or 15 times their body length. [2] (That's roughly equivalent to a human moving at 65 to 97.5 km per hour.) But when they stop turning the flagella, the don't keep coasting as a ship or submarine would. Instead, the surround water stops them in less than the diameter of a water molecule, less than a ten thousandth of their length. [3]

Footnotes

[1] from The Machinery of Life by David Goodsell

[2] 1μm is 0.001 mm -- a millionth, or 10^-6 , of a metre

[3] A water molecule is 3x10^-10 metre (A Sense of Scale)