Editing Froude number (section)

==Origins==
In [[Open-channel flow|open channel flows]], {{harvnb|Belanger|1828|p=}} introduced first the ratio of the flow velocity to the square root of the gravity acceleration times the flow depth. When the ratio was less than unity, the flow behaved like a fluvial motion (i.e., subcritical flow), and like a torrential flow motion when the ratio was greater than unity.{{sfn|Chanson|2009|pp=159–163}}

[[Image:Boat models by William Froude.JPG|thumb|right|The hulls of ''swan'' (above) and ''raven'' (below). A sequence of 3, 6, and 12 (shown in the picture) foot scale models were constructed by Froude and used in towing trials to establish resistance and scaling laws.]] Quantifying resistance of floating objects is generally credited to [[William Froude]], who used a series of scale models to measure the resistance each model offered when towed at a given speed.  The naval constructor [[Frederic Reech]] had put forward the concept much earlier in 1852 for testing ships and propellers but Froude was unaware of it.{{sfn|Normand|1888|pp=257-261}} Speed–length ratio was originally defined by Froude in his ''Law of Comparison'' in 1868 in dimensional terms as:
<math display="block">\text{speed–length ratio} =\frac{u}{\sqrt {\text{LWL}} }</math>
where:
*{{math|''u''}} = flow speed
*{{math|LWL}} = length of waterline

The term was converted into non-dimensional terms and was given Froude's name in recognition of the work he did. In France, it is sometimes called '''Reech–Froude number''' after Frederic Reech.{{sfn|Chanson|2004|p= xxvii}}