n=24;
m= 13;
axis = {1,1};
{a,b}= {0, 1};
f1[x_]=(Sqrt[x])
f2[x_]= x;
Manipulate[
Show[
ParametricPlot3D[ 
{
{x,f1[x]Sin[θ],f1[x]Cos[θ]},
{x,f2[x]Sin[θ],f2[x]Cos[θ]}
},
{x, a, b},
{θ,0, 2 π},
PlotPoints->20,
PlotStyle->Directive[Green,Opacity[0.05],Specularity[White,20]],
Mesh->False
],
ParametricPlot3D[ 
{x,t f1[x] + (1-t) f2[x],0},
{t,0,1},{x, a, b},
Mesh->False
],
ParametricPlot3D[ 
{
{x,f1[x]Cos[θ],f1[x]Sin[θ]},
{x,f2[x]Cos[θ],f2[x]Sin[θ]}
},
{x, a, b},
{θ,0, ϕ},
PlotPoints->20,
PlotStyle->Directive[Blue,Opacity[0.9],Specularity[White,20]],
Mesh->False
],
PlotRange->{{0,1},{-1,1},{-1,1}}
],
{ϕ,0.01, 2π, 2π/24}]