What is Froude's number?

Question

What is Froude's number?

Answer 1

The Froude number is a dimensionless number comparing inertial and gravitational forces. It may be used to quantify the resistance of an object moving through water, and compare objects of different sizes. Named after William Froude, the Froude number is based on his speed/length ratio.

Quantifying resistance of floating objects is generally credited to Froude, who used a series of scale models to measure the resistance each model offered when towed at a given speed. Froude's observations led him to derive the Wave-Line Theory which first described the resistance of a shape as being a function of the waves caused by varying pressures around the hull as it moves through the water. The Naval Constructor Ferdinand Reech had put forward the concept in 1832 but had not demonstrated how it could be applied to practical problems in ship resistance.

Answer 2

Froude's number is the ratio of inertia forces to the gravitational forces. It is used to determine the resistance to a body flowing through a fluid at a specified velocity. Froude's number is equivalent to Mach number in aerodynamics.