Use DO loop in Plot order at mathematica 8

[es.no]

Can anyone help me to in this problem?
I want to use DO loop in Plot order at mathematica 8, how can I do this?
I want to change one variables and see the changes in other variables in the graph, and want to plot all of my graph in one Plot order. Like this.

I Uploaded my file too.

 

[Bill Simpson]

This does not use a Do loop.

Look up Plot in the help system and see that

Plot[{f1,f2,f3} will plot f1 and f2 and f3 on the same graph.

Then realize you can make {f1,f2,f3} using Table[].

Plot[Table[Sqrt[r^2 - x^2], {r, 1, 4}], {x, 0, 4}, AspectRatio -> Automatic]

Or do this the hard and error prone way with a Do loop

r = 4;
plotlist = {};
Do[
AppendTo[plotlist, Plot[Sqrt[r^2 - x^2], {x, 0, 4}]];
r = r - 1
, {4}];
Show[plotlist, AspectRatio -> Automatic]