c219f628b64e0c0690bebcb475d037e6a6a54ce4
   1\documentclass[a4paper, tikz, pstricks]{article}
   2\usepackage[a4paper,margin=2cm]{geometry}
   3\usepackage{array}
   4\usepackage{amsmath}
   5\usepackage{amssymb}
   6\usepackage{tcolorbox}
   7\usepackage{fancyhdr}
   8\usepackage{pgfplots}
   9\usepackage{tikz}
  10\usetikzlibrary{arrows,
  11    calc,
  12    decorations,
  13    scopes,
  14}
  15\usepackage{pst-plot}
  16\psset{dimen=monkey,fillstyle=solid,opacity=.5}
  17\def\object{%
  18    \psframe[linestyle=none,fillcolor=blue](-2,-1)(2,1)
  19    \psaxes[linecolor=gray,labels=none,ticks=none]{->}(0,0)(-3,-3)(3,2)[$x$,0][$y$,90]
  20    \rput{*0}{%
  21        \psline{->}(0,-2)%
  22        \uput[-90]{*0}(0,-2){$\vec{w}$}}
  23}
  24
  25\usepackage{tabularx}
  26\usetikzlibrary{angles}
  27\usepackage{keystroke}
  28\usepackage{listings}
  29\usepackage{xcolor} % used only to show the phantomed stuff
  30\definecolor{cas}{HTML}{e6f0fe}
  31
  32\pagestyle{fancy}
  33\fancyhead[LO,LE]{Year 12 Specialist - Dynamics}
  34\fancyhead[CO,CE]{Andrew Lorimer}
  35
  36\setlength\parindent{0pt}
  37
  38\begin{document}
  39
  40  \title{Dynamics}
  41  \author{}
  42  \date{}
  43  \maketitle
  44
  45  \section{Resolution of forces}
  46
  47  \textbf{Resultant force} is sum of force vectors
  48
  49  \subsection{In angle-magnitude form}
  50
  51  \makebox[3cm]{Cosine rule:} \(c^2=a^2+b^2-2ab\cos\theta\)
  52  \makebox[3cm]{Sine rule:} \(\dfrac{a}{\sin A}=\dfrac{b}{\sin B}=\dfrac{c}{\sin C}\)
  53  
  54  \subsection{In \(\boldsymbol{i}\)---\(\boldsymbol{j}\) form}
  55
  56  Vector of \(a\) N at \(\theta\) to \(x\) axis is equal to \(a \cos \theta \boldsymbol{i} + a \sin \theta \boldsymbol{j}\). Convert all force vectors then add.
  57
  58  To find angle of an \(a\boldsymbol{i} + b\boldsymbol{j}\) vector, use \(\theta = \tan^{-1} \frac{b}{a}\)
  59
  60  \subsection{Resolving in a given direction}
  61
  62  The resolved part of a force \(P\) at angle \(\theta\) is has magnitude \(P \cos \theta\)
  63
  64  To convert force \(||\vec{OA}\) to angle-magnitude form, find component \(\perp\vec{OA}\) then \(|\boldsymbol{r}|=\sqrt{\left(||\vec{OA}\right)^2 + \left(\perp\vec{OA}\right)^2},\quad \theta = \tan^{-1}\dfrac{\perp\vec{OA}}{||\vec{OA}}\)
  65
  66  \section{Newton's laws}
  67  
  68  \begin{enumerate}
  69    \item Velocity is constant without a net external velocity
  70    \item \(\frac{d}{dt} \rho \propto \Sigma F \implies \boldsymbol{F}=m\boldsymbol{a}\)
  71    \item Equal and opposite forces
  72  \end{enumerate}
  73
  74  \subsection{Weight}
  75  A mass of \(m\) kg has force of \(mg\) acting on it
  76
  77  \subsection{Momentum \(\rho\)}
  78  \[ \rho = mv \tag{units kg m/s or Ns} \]
  79
  80  \subsection{Reaction force \(R\)}
  81
  82  \begin{itemize}
  83    \item With no vertical velocity, \(R=mg\)
  84    \item With upwards acceleration, \(R-mg=ma\)
  85    \item With force \(F\) at angle \(\theta\), then \(R=mg-F\sin\theta\)
  86  \end{itemize}
  87
  88  \subsection{Friction}
  89
  90  \[ F_R = \mu R \tag{friction coefficient} \]
  91
  92  \section{Inclined planes}
  93
  94  \[ \boldsymbol{F} = |\boldsymbol{F}| \cos \theta \boldsymbol{i} + |\boldsymbol{F}| \sin \theta \boldsymbol{j} \]
  95 \def\iangle{30} % Angle of the inclined plane
  96
  97    \def\down{-90}
  98    \def\arcr{0.5cm} % Radius of the arc used to indicate angles
  99
 100\begin{tikzpicture}[
 101        >=latex',
 102        scale=1,
 103        force/.style={->,draw=blue,fill=blue},
 104        axis/.style={densely dashed,gray,font=\small},
 105        M/.style={rectangle,draw,fill=lightgray,minimum size=0.5cm,thin},
 106        m/.style={rectangle,draw=black,fill=lightgray,minimum size=0.3cm,thin},
 107        plane/.style={draw=black,fill=blue!10},
 108        string/.style={draw=red, thick},
 109        pulley/.style={thick},
 110        ]
 111        \pgfmathsetmacro{\Fnorme}{2}
 112        \pgfmathsetmacro{\Fangle}{30}
 113        \begin{scope}[rotate=\iangle]
 114            \node[M,transform shape] (M) {};
 115            \coordinate (xmin) at ($(M.south west)-({abs(1.1*\Fnorme*sin(-\Fangle))},0)$);
 116            \coordinate (xmax) at ($(M.south east)+({abs(1.1*\Fnorme*sin(-\Fangle))},0)$);
 117            \coordinate (ymax) at ($(M.north)+(0, {abs(1.1*\Fnorme*cos(-\Fangle))})$);
 118            \coordinate (ymin) at ($(M.south)-(0, 1cm)$);
 119            \coordinate (axiscentre) at ($(M.south)+(0.5cm, 0.5cm)$);
 120            \draw[postaction={decorate, decoration={border, segment length=2pt, angle=-45},draw,red}] (xmin) -- (xmax);
 121            \coordinate (N) at ($(M.center)+(0,{\Fnorme*cos(-\Fangle)})$);
 122            \coordinate (fr) at ($(M.center)+({\Fnorme*sin(-\Fangle)}, 0)$);
 123            % Draw axes and help lines
 124
 125            {[axis,->]
 126                \draw (ymin) -- (ymax) node[right] {\(\boldsymbol{j}\)};
 127                \draw (M) --(M-|xmax) node[right] {\(\boldsymbol{i}\)};    % mental note for me: change "right" to "above"
 128            }
 129
 130            % Forces
 131            {[force,->]
 132                % Assuming that Mg = 1. The normal force will therefore be cos(alpha)
 133                \draw (M.center) -- (N) node [right] {\(R\)};
 134                \draw (M.center) -- (fr) node [left] {\(\mu R\)};
 135            }
 136%            \draw [densely dotted, gray] (fr) |- (N) node [pos=.25, left] {\tiny$\lVert \vec F\rVert\cos\theta$} node [pos=.75, above] {\tiny$\lVert \vec F\rVert\sin\theta$};
 137        \end{scope}
 138        % Draw gravity force. The code is put outside the rotated
 139        % scope for simplicity. No need to do any angle calculations. 
 140        \draw[force,->] (M.center) -- ++(0,-1) node[below] {$mg$};
 141        \draw (M.center)+(-90:\arcr) arc [start angle=-90,end angle=\iangle-90,radius=\arcr] node [below, pos=.5] {\tiny\(\theta\)};
 142    \end{tikzpicture}
 143
 144  \section{Connected particles}
 145
 146  \begin{itemize}
 147    \item \textbf{Suspended pulley:} tension in both sections of rope are equal
 148    \item \textbf{Linear connection:} find acceleration of system first
 149    \item \textbf{Pulley on edge of incline:} find downwards force \(W_2\) and components of mass on plane
 150  \end{itemize}
 151\def\iangle{25} % Angle of the inclined plane
 152
 153\def\down{-90}
 154\def\arcr{0.5cm} % Radius of the arc used to indicate angles
 155
 156{\begin{centering} {\begin{tikzpicture}[
 157    force/.style={>=latex,draw=blue,fill=blue},
 158    axis/.style={densely dashed,gray,font=\small},
 159    M/.style={rectangle,draw,fill=lightgray,minimum size=0.6cm,thin},
 160    m/.style={rectangle,draw=black,fill=lightgray,minimum size=0.3cm,thin},
 161    plane/.style={draw=black,fill=blue!10},
 162    string/.style={draw=red, thick},
 163    pulley/.style={thick},
 164    scale=1.5
 165]
 166
 167\matrix[column sep=1cm] {
 168    %% Sketch
 169    \draw[plane] (0,-1) coordinate (base)
 170                     -- coordinate[pos=0.5] (mid) ++(\iangle:3) coordinate (top)
 171                     |- (base) -- cycle;
 172    \path (mid) node[M,rotate=\iangle,yshift=0.3cm,font=\footnotesize] (M) {\(m_1\)};
 173    \draw[pulley] (top) -- ++(\iangle:0.25) circle (0.25cm)
 174                   ++ (90-\iangle:0.5) coordinate (pulley);
 175    \draw[string] (M.east) -- ++(\iangle:1.4cm) arc (90+\iangle:0:0.25)
 176                  -- ++(0,-1) node[m,font=\scriptsize] {\(m_2\)};
 177
 178    \draw[->] (base)++(\arcr,0) arc (0:\iangle:\arcr);
 179    \path (base)++(\iangle*0.5:\arcr+5pt) node {\(\theta\)};
 180    %%
 181
 182&
 183    %% Free body diagram of m1
 184    \begin{scope}[rotate=\iangle]
 185        \node[M,transform shape] (M) {};
 186        % Draw axes and help lines
 187
 188        {[axis,->]
 189            \draw (0,-1) -- (0,2) node[right] {\(+\boldsymbol{i}\)};
 190            \draw (M) -- ++(2,0) node[right] {\(+\boldsymbol{j}\)};
 191            % Indicate angle. The code is a bit awkward.
 192
 193            \draw[solid,shorten >=0.5pt] (\down-\iangle:\arcr)
 194                arc(\down-\iangle:\down:\arcr);
 195            \node at (\down-0.5*\iangle:1.3*\arcr) {\(\theta\)};
 196        }
 197
 198        % Forces
 199        {[force,->]
 200            % Assuming that Mg = 1. The normal force will therefore be cos(alpha)
 201            \draw (M.center) -- ++(0,{cos(\iangle)}) node[above right] {$N$};
 202            \draw (M.west) -- ++(-1,0) node[left] {\(F_R\)};
 203            \draw (M.east) -- ++(1,0) node[above] {\(T_1\)};
 204        }
 205
 206    \end{scope}
 207    % Draw gravity force. The code is put outside the rotated
 208    % scope for simplicity. No need to do any angle calculations. 
 209    \draw[force,->] (M.center) -- ++(0,-1) node[below] {\(m_1g\)};
 210    %%
 211
 212&
 213    %%%
 214    % Free body diagram of m2
 215    \node[m] (m) {};
 216    \draw[axis,->] (m) -- ++(0,-2) node[left] {$+$};
 217    {[force,->]
 218        \draw (m.north) -- ++(0,1) node[above] {\(T_2\)};
 219        \draw (m.south) -- ++(0,-1) node[right] {\(m_2g\)};
 220    }
 221
 222\\
 223};
 224\end{tikzpicture}}\end{centering} }
 225    \section{Equilibrium}
 226
 227    \[ \dfrac{A}{\sin a} = \dfrac{B}{\sin b} = \dfrac{C}{\sin c} \tag{Lami's theorem}\]
 228
 229    Three methods:
 230    \begin{enumerate}
 231      \item Lami's theorem (sine rule)
 232      \item Triangle of forces or CAS (use to verify)
 233      \item Resolution of forces (\(\Sigma F = 0\) - simultaneous)
 234    \end{enumerate}
 235
 236
 237    \colorbox{cas}{On CAS:} use Geometry, lock known constants.
 238
 239
 240\end{document}