I don't know about what is Wikipedia, and given more solid experimentially derived infromation, I really don't care what they say.
First question for them: Are they talking about movement in air or in water? Both gases and liquids are classified as fluids, but there is considerable difference in their response. First and foremost, gases are compressible, and liquids, water at least, for all practical purposes are not compressible.
I will copy in here what I said elsewhere, as this is really the more appropriate thread anyway.
Train resistance is most simply expressed in the form of a TR = A + B V + C V^2 formula, where "V" is the speed and the A, B, and C are constants.
Formulas of this nature have been used for many years. Search "Davis Formula" for the granddaddy of all these things. V^3 terms? Not in any of them.
In general,
"A" represents starting resistance and internal machine friction, and is constant regardless of speed.
"B" represents resistance due to deflection of the track and deviations from perfect smoothness of track
"C" is primarily aerodynamic
"A" and "B" are both relative to train weight, when different lengths of trains of the same equipment are analyzed. "C" includes a front end constant plus a length factor.
For high speed trainsets operating on tracks permitting high speed operation, both the "A" and the "B" terms are relatively small, and become less and less significant as actual speed increases.
All these terms are derived primarily from measurements of actual train performance as determined by power draw in relation to speed and acceleration. Since proper derivation of these terms is quite expensive, the results are usually not published.
If doing this for freight, the terms can be extrodinarily complex, as A, B, and C depend upon the characteristics of each piece of equipment, and, for the "C" term its relationship to its neighbors in the makeup of the train.
Power and tractive effort: TE = P/V. Therefore, TE is infinite at a speed of zero. This obviously is not possible, and even if possible could not be applied to the rail. Generally, at low speeds TE is limited based on a permissible acceleration rate.
Adhesion has also been determined to decline with speed. Usually this is not a factor in EMU's, but can be with high powered light axle load locomotives.
Again, this factor is experimentially determined. One set of formulae is in the form of Adhesion = D / (V + E), where D and E are constants and V is the speed. Usually there are multiple values used here, one for dry rail which is effectively the maximum, another for wet rail, which is the maximum to be considered in scheduling, and a third for braking which is a worst condition situation that you had better consider in determining safe stopping distances. For the accelerating condition, the factor must be multiplied by the proportion of the train weigth on powered axles. For braking, the full weight may be used, or a reduced factor based on some ratio of failed brakes included.
Numbers: All these are in metric units, because that is the way I have dealt with these things. The numbers given are not the real ones, as these are regarded as confidential by the equipment supplier, but the are in the general range of those that are used.
For train resistance for high speed train sets, with "V" in km/h and resitance in kilonewtons, think of something on the order of: 8.00 + 0.08 V + 0.0008 V^2 for a train with a weigth of around 600 metric tonnes.
For power, think in terms of motors of around 275 to 325 kilowatts each times however many axles you feel like so long as your weigth per axle is in the range of 13 to 16 tonnes. To get TE, you must convert the "V" term from km/h to meters/second.
For adhesion, the Shinkansen braking adhesion formula was published in AREA Bulletin No.727, October 1990. It is
Adhesion = 13.6 / (V + 85) again, remember these are metric units.
Also this is a ratio, so at say 200 km/h, the Adhesion is 4.77%. If this sounds low, it is. The braking rate is somewhat higher than this, because braking is assisted by train resistance.
End of lesson.
All further work is left to the student.
Discussion of power requirements will be in a later installment.