diff --git a/4-11.html b/4-11.html
new file mode 100644
index 0000000..56f678c
--- /dev/null
+++ b/4-11.html
@@ -0,0 +1,176 @@
+<!--
+    This work is licensed under CC BY-NC-ND 4.0            
+    Link to license: http://creativecommons.org/licenses/by-nc-nd/4.0/
+    Attribute to Russell Georgi
+-->
+<html>
+    <head>
+        <title>
+            Problem 4-11
+        </title>
+        <style>
+            html, body {
+                width:  100%;
+                height: 100%;
+                margin: 0px;
+                border: 0;
+                overflow: hidden;
+                display: block;
+            }
+
+            canvas {
+                position: absolute;
+            }
+
+                        
+            .dropbtn {
+              background-color: #04AA6D;
+              color: white;
+              padding: 16px;
+              font-size: 16px;
+              border: none;
+            }
+            
+            .dropdown {
+              position: absolute;
+              display: inline-block;
+            }
+            
+            .dropdown-content {
+              display: none;
+              position: relative;
+              background-color: #f1f1f1;
+              box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
+              z-index: 1;
+            }
+            
+            .dropdown-content button {
+              color: black;
+              padding: 12px 16px;
+              width: 100px;
+              text-decoration: none;
+              display: block;
+            }
+            
+            .dropdown-content a:hover {background-color: #ddd;}
+            
+            .dropdown:hover .dropdown-content {display: block;}
+            
+            .dropdown:hover .dropbtn {background-color: #3e8e41;}
+        </style>
+    </head>
+    <body>       
+        <canvas id="myCanvas" width="1" height="1" style="border:1px solid #ffffff;">
+        Your browser does not support the HTML5 canvas tag.</canvas>
+        <div class="dropdown">
+            <button class="dropbtn" id="btn">Mode 1</button>
+            <div class="dropdown-content">
+              <button onclick="num(0)">Mode 1</button>
+              <button onclick="num(1)">Mode 2</button>
+            </div>
+        </div>  
+        
+        <script>
+        var c = document.getElementById("myCanvas");
+        var ctx = c.getContext("2d");
+        ctx.canvas.width = window.innerWidth;
+        ctx.canvas.height = window.innerHeight;
+    
+        var w = 1;
+        var wd = 1;
+        var fd = 20;
+        var m = 1;
+        var t = 0;
+        var dt = 0.1;
+        var xPos = 0;
+        var yPos = 0;
+
+
+        ctx.translate(ctx.canvas.width / 2, ctx.canvas.height / 2);
+        ctx.scale(1.5, 1.5);
+
+
+        function Clear(ctx)
+        {
+            ctx.clearRect(-c.width, -c.height, c.width * 2, c.height * 2);
+        }
+
+        function Update()
+        {
+            Clear(ctx);
+            Draw();
+            t += dt;
+           
+            setTimeout(Update, 1000/60)
+        }
+
+        function Draw()
+        {
+            ctx.beginPath();
+            ctx.arc(xPos, yPos, 100, 0, Math.PI * 2);
+            ctx.stroke();
+            var x1 = -fd * (2 * w * w - wd * wd) * Math.cos(wd * t) / 
+                (wd * wd * (4 * w * w - wd * wd) * m);
+            var y1 = Math.sqrt(10000 - x1 * x1);
+            var t1 = Math.atan(y1 / x1);
+            var x2 = -fd * 2 * Math.cos(wd * t) / 
+                (wd * wd * (4 * w * w - wd * wd) * m);
+            var y2 = -Math.sqrt(10000 - x2 * x2);
+            var t2 = Math.atan(y2 / x2);
+            
+            if (x1 < 0 || y1 < 0)
+            {
+                t1 += Math.PI;
+            }
+            if (x2 < 0)
+            {
+                t2 -= Math.PI;
+            }
+            ctx.beginPath();
+            ctx.arc(xPos + x1, yPos + y1, 10, 0, Math.PI * 2);
+            ctx.fill();
+            ctx.beginPath();
+            ctx.arc(xPos + x2, yPos + y2, 10, 0, Math.PI * 2);
+            ctx.fill();
+            drawSpring(1, 3, Math.abs(t2 - t1), -10, 20, Math.min(t1, t2) - Math.PI / 2 + 0.2, 105, 0.1, xPos, yPos);
+            drawSpring(1, 3, Math.PI * 2 - Math.abs(t2 - t1) -0.1, -10, 20, Math.max(t1, t2) - Math.PI / 2 + 0.2, 105, 0.1, xPos, yPos);
+        }
+
+        function drawSpring(a, b, tSize, rSize, numLoops, t, r, pStep, x, y)
+        {
+            var pStart = Math.PI / 2;
+            var pEnd = (3 * Math.PI / 2) + (2 * Math.PI * numLoops);
+            var tEnd = a * pEnd - b * Math.sin(pEnd);
+            var rEnd = a + b;
+            var tFactor = tSize / tEnd;
+            var rFactor = rSize / rEnd;
+            var tShift = t - a * (Math.PI / 2) + b * Math.sin(Math.PI / 2);
+            var rShift = r - a + b * Math.cos(Math.PI / 2);
+            for (p = pStart; p <= pEnd; p += pStep)
+            {
+                var theta = tShift + tFactor * (a * p - b * Math.sin(p));
+                var radius = rShift + rFactor * (a - b * Math.cos(p));
+                ctx.beginPath();
+                ctx.moveTo(x + radius * Math.cos(theta), y + radius * Math.sin(theta));
+                theta = tShift + tFactor * (a * (p + pStep) - b * Math.sin((p + pStep)));
+                radius = rShift + rFactor * (a - b * Math.cos(p + pStep));
+                ctx.lineTo(x + radius * Math.cos(theta), y + radius * Math.sin(theta));
+                ctx.stroke();
+            }
+        }
+
+        window.addEventListener('resize', function(event) {
+            c.width = window.innerWidth;
+            c.height = window.innerHeight;
+            ctx.translate(c.width / 2, c.height / 2);
+            ctx.scale(1.5, 1.5);
+        }, true);
+
+        Update();
+
+        </script>
+    </body>
+    <p xmlns:cc="http://creativecommons.org/ns#" style="font-size: 1vw; bottom: 0px; position: absolute;">
+        This work is licensed under 
+        <a href="http://creativecommons.org/licenses/by-nc-nd/4.0/?ref=chooser-v1" target="_blank" rel="license noopener noreferrer" style="display:inline-block;">CC BY-NC-ND 4.0<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;" src="https://mirrors.creativecommons.org/presskit/icons/cc.svg?ref=chooser-v1"><img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;" src="https://mirrors.creativecommons.org/presskit/icons/by.svg?ref=chooser-v1"><img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;" src="https://mirrors.creativecommons.org/presskit/icons/nc.svg?ref=chooser-v1"><img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;" src="https://mirrors.creativecommons.org/presskit/icons/nd.svg?ref=chooser-v1"></a></p>
+</html>
\ No newline at end of file
diff --git a/4-9.html b/4-9.html
new file mode 100644
index 0000000..f2ce47b
--- /dev/null
+++ b/4-9.html
@@ -0,0 +1,172 @@
+<!--
+    This work is licensed under CC BY-NC-ND 4.0            
+    Link to license: http://creativecommons.org/licenses/by-nc-nd/4.0/
+    Attribute to Russell Georgi
+-->
+<html>
+    <head>
+        <title>
+            Problem 4-9
+        </title>
+        <style>
+            html, body {
+                width:  100%;
+                height: 100%;
+                margin: 0px;
+                border: 0;
+                overflow: hidden;
+                display: block;
+            }
+
+            canvas {
+                position: absolute;
+            }
+
+                        
+            .dropbtn {
+              background-color: #04AA6D;
+              color: white;
+              padding: 16px;
+              font-size: 16px;
+              border: none;
+            }
+            
+            .dropdown {
+              position: absolute;
+              display: inline-block;
+            }
+            
+            .dropdown-content {
+              display: none;
+              position: relative;
+              background-color: #f1f1f1;
+              box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
+              z-index: 1;
+            }
+            
+            .dropdown-content button {
+              color: black;
+              padding: 12px 16px;
+              width: 100px;
+              text-decoration: none;
+              display: block;
+            }
+            
+            .dropdown-content a:hover {background-color: #ddd;}
+            
+            .dropdown:hover .dropdown-content {display: block;}
+            
+            .dropdown:hover .dropbtn {background-color: #3e8e41;}
+        </style>
+    </head>
+    <body>       
+        <canvas id="myCanvas" width="1" height="1" style="border:1px solid #ffffff;">
+        Your browser does not support the HTML5 canvas tag.</canvas>
+        <div class="dropdown">
+            <button class="dropbtn" id="btn">Mode 1</button>
+            <div class="dropdown-content">
+              <button onclick="num(0)">Mode 1</button>
+              <button onclick="num(1)">Mode 2</button>
+            </div>
+        </div>  
+        
+        <script>
+        var c = document.getElementById("myCanvas");
+        var ctx = c.getContext("2d");
+        ctx.canvas.width = window.innerWidth;
+        ctx.canvas.height = window.innerHeight;
+    
+        var w = 1;
+        var amp = 20;
+        var mode = 0;
+        var t = 0;
+        var dt = 0.1;
+        var xPos = 0;
+        var yPos = 0;
+
+        function num(n)
+        {
+            mode = n;
+        }
+
+
+        ctx.translate(ctx.canvas.width / 2, ctx.canvas.height / 2);
+        ctx.scale(1.5, 1.5);
+
+
+        function Clear(ctx)
+        {
+            ctx.clearRect(-c.width, -c.height, c.width * 2, c.height * 2);
+        }
+
+        function Update()
+        {
+            Draw();
+            t += dt;
+            setTimeout(Update, 1000/60)
+        }
+
+        function Draw()
+        {
+            if (mode == 0)
+            {
+                Clear(ctx);
+                ctx.beginPath();
+                ctx.arc(xPos + 50 + amp * Math.sin(w * t), yPos, 5, 0, Math.PI * 2);
+                ctx.fill();
+                ctx.beginPath();
+                ctx.arc(xPos - 50 + amp * (Math.sqrt(3) - 1) * Math.sin(w * t) / 2, yPos, 5 * Math.sqrt(2), 0, Math.PI * 2);
+                ctx.fill();
+                drawSpring(1, 3, 100 + amp * (Math.sqrt(3) - 1) * Math.sin(w * t) / 2, 10, 5, xPos - 150, yPos, 0.1, 0);
+                drawSpring(1, 3, 100 - amp * (Math.sqrt(3) - 1) * Math.sin(w * t) / 2+ amp * Math.sin(w * t), 10, 5, xPos - 50 + amp * (Math.sqrt(3) - 1) * Math.sin(w * t) / 2, yPos, 0.1, 0);
+                drawSpring(1, 3, 100 - amp * Math.sin(w * t) , 10, 5, xPos + 50 + amp * Math.sin(w * t), yPos, 0.1, 0);
+            } else if (mode == 1)
+            {
+                Clear(ctx);
+                ctx.beginPath();
+                ctx.arc(xPos + 50 + amp * Math.sin(w * t), yPos, 5, 0, Math.PI * 2);
+                ctx.fill();
+                ctx.beginPath();
+                ctx.arc(xPos - 50 + amp * (-Math.sqrt(3) - 1) * Math.sin(w * t) / 2, yPos, 5 * Math.sqrt(2), 0, Math.PI * 2);
+                ctx.fill();
+                drawSpring(1, 3, 100 + amp * (-Math.sqrt(3) - 1) * Math.sin(w * t) / 2, 10, 5, xPos - 150, yPos, 0.1, 0);
+                drawSpring(1, 3, 100 - amp * (-Math.sqrt(3) - 1) * Math.sin(w * t) / 2+ amp * Math.sin(w * t), 10, 5, xPos - 50 + amp * (-Math.sqrt(3) - 1) * Math.sin(w * t) / 2, yPos, 0.1, 0);
+                drawSpring(1, 3, 100 - amp * Math.sin(w * t) , 10, 5, xPos + 50 + amp * Math.sin(w * t), yPos, 0.1, 0);
+            }
+        }
+
+        function drawSpring(a, b, tSize, rSize, numLoops, x, y, tStep, deltaY)
+        {
+            var tStart = Math.PI / 2;
+            var tEnd = (3 * Math.PI / 2) + (2 * Math.PI * numLoops);
+            var xEnd = a * tEnd - b * Math.sin(tEnd);
+            var yEnd = a + b;
+            var xFactor = xSize / xEnd;
+            var yFactor = ySize / yEnd;
+            var xShift = x - a * (Math.PI / 2) + b * Math.sin(Math.PI / 2);
+            var yShift = y - a + b * Math.cos(Math.PI / 2);
+            var slope = deltaY / xSize;
+            for (p = tStart; p <= tEnd; p += tStep)
+            {
+                ctx.beginPath();
+                ctx.moveTo(xShift + xFactor * (a * p - b * Math.sin(p)), yShift + yFactor * (a - b * Math.cos(p)) + slope * (a * p - b * Math.sin(p)));
+                ctx.lineTo(xShift + xFactor * (a * (p + tStep) - b * Math.sin(p + tStep)), yShift + yFactor * (a - b * Math.cos(p + tStep)));
+                ctx.stroke();
+            }
+        }
+
+        window.addEventListener('resize', function(event) {
+            c.width = window.innerWidth;
+            c.height = window.innerHeight;
+            ctx.translate(c.width / 2, c.height / 2);
+            ctx.scale(1.5, 1.5);
+        }, true);
+
+        Update();
+
+        </script>
+    </body>
+    <p xmlns:cc="http://creativecommons.org/ns#" style="font-size: 1vw; bottom: 0px; position: absolute;">
+        This work is licensed under 
+        <a href="http://creativecommons.org/licenses/by-nc-nd/4.0/?ref=chooser-v1" target="_blank" rel="license noopener noreferrer" style="display:inline-block;">CC BY-NC-ND 4.0<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;" src="https://mirrors.creativecommons.org/presskit/icons/cc.svg?ref=chooser-v1"><img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;" src="https://mirrors.creativecommons.org/presskit/icons/by.svg?ref=chooser-v1"><img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;" src="https://mirrors.creativecommons.org/presskit/icons/nc.svg?ref=chooser-v1"><img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;" src="https://mirrors.creativecommons.org/presskit/icons/nd.svg?ref=chooser-v1"></a></p>
+</html>
\ No newline at end of file
