title: Bouncing ball issue
body: <p>I am currently working on the 2D Bouncing ball physics that bounces the ball up and down. The physics behaviour works fine but at the end the velocity keep +3 then 0 non-stop even the ball has stopped bouncing. How should I modify the code to fix this issue? </p>
  
  <p>Here is the video shows how it works. 
  Note: Bandicam cannot record the velocity transition between -3 and 0. So, it just shows -3 when the ball stops bouncing.<br>
  <a href="https://www.youtube.com/watch?v=SEH5V6FBbYA&amp;feature=youtu.be" rel="nofollow noreferrer">https://www.youtube.com/watch?v=SEH5V6FBbYA&amp;feature=youtu.be</a></p>
  
  <p>Here is the generated report: <a href="https://www.dropbox.com/s/4dkt0sgmrgw8pqi/report.txt" rel="nofollow noreferrer">https://www.dropbox.com/s/4dkt0sgmrgw8pqi/report.txt</a></p>
  
  <pre><code>    ballPos         = D3DXVECTOR2( 50, 100 );
      velocity        = 0;
      acceleration    = 3.0f;
      isBallUp        = false;
  
  void GameClass::Update()
  {
      // v = u + at
      velocity += acceleration;
  
      // update ball position
      ballPos.y += velocity;
  
      // If the ball touches the ground
      if ( ballPos.y &gt;= 590 )
      {
          // Bounce the ball
          ballPos.y = 590;
          velocity *= -1;
      }
  
      // Graphics Rendering
      m_Graphics.BeginFrame();
      ComposeFrame();
      m_Graphics.EndFrame();
  }
  </code></pre>