Plotting Log as part of an equation in mathematica

[nimbus2506]

Hello I'm trying to plot log as part of an equation in mathematica and it does not seem to be working for me.

for example I'm using Plot y = 25x / log10 (x) - 50x

I'm just experimenting with different numbers and formulas to see what happens to the log curve.

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What I'm doing in more detail, is that I want to be able to change variables so that the curve can become steeper or shallower. I want to introduce about 4 or 5 different variables to control it.

http://en.wikipedia.org/wiki/File:WellHead.gif

I want to try and mimic and simplify this formula to produce the graph above. Where the water table level is controlled by the porosity of the rock and the flow of the well. Low porosity and low discharge from the well result in a steep curve and vise versa.

Q = 2π K (Db - Dm) (Dw - Dm) / ln (Ri/Rw)

where Q = safe well discharge - i.e. the steady state discharge at which no overdraught or groundwater depletion occurs - (m3/day), K = uniform hydraulic conductivity of the soil (m/day), D = depth below soil surface, Db = depth of the bottom of the well equal to the depth of the impermeable base (m), Dm = depth of the watertable midway between the wells (m), Dw is the depth of the water level inside the well (m), Ri = radius of influence of the well (m), Rw=radius of the well (m), ln = natural logarithm, and π = the number pi.

The radius of influence of the wells depends on the pattern of the well field, which may be triangular, square, or rectangular. It can be found as:

Ri = sqrt (At/πN)

http://en.wikipedia.org/wiki/Well_drainage

 

[Bill Simpson]

For base 10 log

Plot[25x / Log[10,x] - 50x,{x,1,100}]

For natural log

Plot[2π K (Db - Dm) (Dw - Dm) / Log[Ri/Rw],{something,somethingelse,somethingother}]