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Dimensional analysis
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=== Rayleigh's method === In dimensional analysis, '''Rayleigh's method''' is a conceptual tool used in [[physics]], [[chemistry]], and [[engineering]]. It expresses a [[functional relationship]] of some [[variable (mathematics)|variables]] in the form of an [[exponential equation]]. It was named after [[Lord Rayleigh]]. The method involves the following steps: # Gather all the [[independent variable]]s that are likely to influence the [[dependent variable]]. # If {{math|''R''}} is a variable that depends upon independent variables {{math|''R''<sub>1</sub>}}, {{math|''R''<sub>2</sub>}}, {{math|''R''<sub>3</sub>}}, ..., {{math|''R''<sub>''n''</sub>}}, then the [[functional equation]] can be written as {{math|1=''R'' = ''F''(''R''<sub>1</sub>, ''R''<sub>2</sub>, ''R''<sub>3</sub>, ..., ''R''<sub>''n''</sub>)}}. # Write the above equation in the form {{math|1=''R'' = ''C'' ''R''<sub>1</sub><sup>''a''</sup> ''R''<sub>2</sub><sup>''b''</sup> ''R''<sub>3</sub><sup>''c''</sup> ... ''R''<sub>''n''</sub><sup>''m''</sup>}}, where {{math|''C''}} is a [[dimensionless constant]] and {{math|''a''}}, {{math|''b''}}, {{math|''c''}}, ..., {{math|''m''}} are arbitrary exponents. # Express each of the quantities in the equation in some [[Base unit (measurement)|base unit]]s in which the solution is required. # By using [[#Dimensional homogeneity|dimensional homogeneity]], obtain a [[set (mathematics)|set]] of [[simultaneous equations]] involving the exponents {{math|''a''}}, {{math|''b''}}, {{math|''c''}}, ..., {{math|''m''}}. # [[Equation solving|Solve]] these equations to obtain the values of the exponents {{math|''a''}}, {{math|''b''}}, {{math|''c''}}, ..., {{math|''m''}}. # [[Simultaneous equations#Substitution method|Substitute]] the values of exponents in the main equation, and form the [[non-dimensional]] [[parameter]]s by [[Combining like terms|grouping]] the variables with like exponents. As a drawback, Rayleigh's method does not provide any information regarding number of dimensionless groups to be obtained as a result of dimensional analysis.
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