有摩擦的斜面

Question

我如何在以下 TikZ 绘图中在框 $M$ 下方绘制摩擦线……？

\begin{figure}[h]
            \centering
            \begin{tikzpicture} [font = \small]
                
                % triangle:
                \draw [draw = orange, fill = orange!15] (0,0) coordinate (O) -- (\ang:6)
                coordinate [pos=.45] (M) |- coordinate (B) (O);
                
                % angles:
                \draw [draw = orange] (O) ++(.8,0) arc (0:\ang:0.8) 
                node [pos=.4, left] {$\theta$};
                \draw [draw = orange] (B) rectangle ++(-0.3,0.3);
                
                \begin{scope} [-latex,rotate=\ang]
                    % Object (rectangle)
                    \draw [fill = purple!30,
                    draw = purple!50] (M) rectangle node [] {$M$} ++ (1,.6) ;
                \end{scope}
                
            \end{tikzpicture}
        \end{figure}

Answer 1

我不完全确定这是否是你想要的，但解决方案参考我的其他答案可能：

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{patterns}

\begin{document}
\begin{tikzpicture}[font=\small]

    \pgfmathsetmacro{\ang}{30}
                
    % triangle:
    \begin{scope}
        \path[save path=\triangle, clip] (0,0) coordinate (O) 
            -- (\ang:6) coordinate[pos=.45] (M) |- coordinate (B) cycle;
        \fill[orange!15] [use path=\triangle];
        \fill[pattern=vertical lines, pattern color=orange!50] (O) -- (\ang:6) -- ++(0,-.25) -- (0,-.25) -- cycle;
    \end{scope}
    \draw[orange] [use path=\triangle];
    
    % angles:
    \draw[orange] (O) ++(.8,0) arc[start angle=0, end angle={\ang}, radius=0.8]
        node[pos=.4, left, black] {$\theta$};
    \draw[orange] (B) rectangle ++(-0.3,0.3);
    
    \begin{scope}[rotate=\ang]
        % Object (rectangle)
        \draw[purple!50, fill=purple!30] (M) rectangle node[black] {$M$} ++(1,.6);
    \end{scope}
    
\end{tikzpicture}
\end{document}

请注意，我使用了三次相同的路径：用图案裁剪形状、填充三角形并最终绘制轮廓。这可能不是最好的解决方案。

另一种解决方案可能是使用图案计算形状的精确坐标，如下所示：

\draw[orange, fill=orange!15] (0,0) coordinate (O) 
    -- (\ang:6) coordinate[pos=.45] (M) |- coordinate (B) cycle;
\fill[pattern=vertical lines, pattern color=orange!50] (O) 
    -- (\ang:6) -- ++(0,-.25) -- ({.25/tan(\ang)},0) -- cycle;

那么就不需要剪切和重新使用路径了。

---

正如@MS-SPO 指出的那样，您可能还想将摩擦线添加到矩形物体：

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{patterns}

\begin{document}
\begin{tikzpicture}[font=\small]

    \pgfmathsetmacro{\ang}{30}
                
    % triangle:
    \draw[orange, fill=orange!15] (0,0) coordinate (O) 
        -- (\ang:6) coordinate[pos=.45] (M) |- coordinate (B) cycle;
    \fill[pattern=vertical lines, pattern color=orange!50] (O) 
        -- (\ang:6) -- ++(0,-.25) -- ({.25/tan(\ang)},0) -- cycle;
    
    % angles:
    \draw[orange] (O) ++(.8,0) arc[start angle=0, end angle={\ang}, radius=0.8]
        node[pos=.4, left, black] {$\theta$};
    \draw[orange] (B) rectangle ++(-0.3,0.3);
    
    \begin{scope}[rotate=\ang]
        % Object (rectangle)
        \draw[purple!50, fill=purple!30] (M) rectangle node[black] {$M$} ++(1,.6);
        \fill[pattern=vertical lines, pattern color=purple!45] 
            (M) rectangle ++(1,.25);
    \end{scope}
    
\end{tikzpicture}
\end{document}