Edit in JSFiddle

/* Spring stiffness, in kg / s^2 */
/*var k = -20;*/
var spring_length = 180;

/* Damping constant, in kg / s */
/*var b = -0.5;*/

/* Block position and velocity. */
/*var block = {x: 100, v: 0, mass: 0.5};*/
var wall  = {x: 20,  lx: 30, v: 0, t: 0, frequency: 0, a: 0};

var frameRate  = 1/30;
var frameDelay = frameRate * 1000;

var canvas;
var ctx;
var width  = 200;
var height = 200;

var loop = function() {
    /* Move the wall. */
    wall.t += frameRate;
    wall.lx = wall.x;
    wall.x = wall.a *  Math.sin(2 * Math.PI * wall.frequency * wall.t);
    wall.v = (wall.x - wall.lx) / frameRate;

    /* Drawing */
    ctx.clearRect(0, 0, width, height);

    ctx.save();

    ctx.fillStyle = '#CCCCCC';
    ctx.fillRect((width/2)-20, height/2 - (wall.x-5), 40, 10);
    ctx.restore();

};

var setup = function() {
    canvas = document.getElementById('canvas');
    ctx = canvas.getContext('2d');

    document.getElementById('a_slider').onchange = function() {
        this.innerHTML = this.value;
        wall.a = 1 * parseFloat(this.value);
        document.getElementById('a_slider_label').innerHTML = wall.a;
    };

    document.getElementById('f_slider').onchange = function() {
        this.innerHTML = this.value;
        wall.frequency = parseFloat(this.value);
        document.getElementById('f_slider_label').innerHTML = wall.frequency;
    };

    setInterval(loop, frameDelay);

};


setup();

<canvas id="canvas" width=200 height=200></canvas>
<div class="controls">

  <div>
    <label>Amplitude (<span id="a_slider_label">0</span>)</label>
    <input id="a_slider" type="range" min=0 max=20 value=0 step=0.1></input>
  </div>
  <div>
    <label>Frequency (<span id="f_slider_label">0</span>) Hz</label>
    <input id="f_slider" type="range" min=0 max=5 value=0 step=0.1></input>
  </div>


</div>

        body {
          font-family: Helvetica, Arial, sans-serif;
          font-size: 12px;
        }
        
        canvas {
          display: block;
          margin: 20px auto;
          width: 200px;
          height: 200px;
          border: 1px solid #333;
        }
        
        .controls {
          width: 400px;
          margin: 10px auto;
        }
        
        .controls > div {
          border-bottom: 1px solid #EEE;
          padding: 5px 0;
        }
        
        .controls label {
          width: 200px;
          display: inline-block;
        }
        
        .controls input {
          vertical-align: middle;
        }