Cannot get sin and cos to display in TIKZ

Question

I have the following code which I took from another site and was trying to adapt in order to plot a sin function and a cos function stacked up one on top of each other:

\def\xs{1}
\def\ys{6}

\begin{tikzpicture}[domain=-3:5, xscale=\xs, yscale=\ys, >=latex]
  \def\tr{0.1}
  \def\ts{0.6}
  \def\al{1.3}
  \def\n{1.6}
  \def\I{0.3506}
  \def\ti{0.4071}
  \def\S{-0.1340}
  \def\Sangle{-42}
  \def\f1{0.8}

  % Function1
  \draw[very thin,color=gray!30] (-3-0.2/\xs,0-0.2/\ys)
    grid[xstep=0.5, ystep=0.1] (5+0.2/\xs,0.7+0.2/\ys);
  \draw[->, line width=1pt] (-3,0) -- (5.25,0)
    node[below] {$r$};
  \draw[->, line width=1pt] (-3,0) -- (-3,0.75)
    node[left] {$f_\phi$};
  % function
  \draw [red,thick,smooth,domain=0:5] plot (\x, {cos(\x)});
  % side decoration
  \draw[dashed] (\I,0) node[below] {$I$} -- (\I,\ti) -- (-3,\ti)
    node[left] {$u_i$};
  \draw [decorate, decoration={brace, amplitude=4pt}]
    (-3.5,\tr) -- (-3.5,\ts) node [black,midway,left=3pt] {$\Delta$};
  % texto
  \path[->, draw]
    (\I,\ti) to[out=0, in=180] ++(0.75,0.1)
    node[anchor=west, text ragged, text width=1.6cm, fill=white]
    {Point of interest};
  \node[above] at (1,0.7)
    {Function $f_\phi$ definition};

  % Function 2
  \def\ys{3}
  \begin{scope}[yshift=-0.3cm, domain=0:10, >=latex, yscale=\ys]
    \draw[very thin,color=gray!30] (-3-0.2/\xs,-0.15-0.15*0.2/\ys)
      grid[xstep=0.5, ystep=0.03] (5+0.2/\xs,0.03+0.15*0.2/\ys);
    \draw[->, line width=1pt] (-3,-0.15) -- (5.25,-0.15)
      node[below] {$\log(\psi)$};
    \draw[->, line width=1pt] (-3,-0.15) -- (-3,0.05)
      node[left] {$U'(\psi)$};
    \draw [green,domain=0:5] plot (\x, {sin(\x)});
    \node[left] at (-3,0) {$0$};
    \draw[dashed] (\I,0.03) -- (\I,\S) -- (-3,\S) node[left] {$U'(I)$};
    \path[->, draw]
      (\I,\S) to[out=-2, in=180] ++(1.75,0.02)
      node[anchor=west, fill=white] {$S$};
    \node[above] at (1,0.03) {Function $F_\phi$ definition};
  \end{scope}
\end{tikzpicture}

But I get lines!!!

I have tried changing the domain range and the scale values. I don't really understand what's happening here! How can I get my functions to display?

Thanks