title: Collision detection without impecting in Box2d Javascript
body: <p>I am creating a Car Race Game, Where i need help in Car over some rough surface area by Box2d Javascript.</p>
  
  <ol>
  <li>I created Car game by following link
  <a href="http://www.codekites.com/make-racing-car-box2d-javascript/" rel="nofollow">http://www.codekites.com/make-racing-car-box2d-javascript/</a></li>
  <li>Also created obstacles. </li>
  </ol>
  
  <p><strong>Question:</strong> </p>
  
  <ol>
  <li>Now i want such obstacles, which should not be collide with Car. But when Car goes over that shape, then Car become slow.</li>
  </ol>
  
  <p>So please help me, how to go with that. i found IsSensor, but that is not working. So please let me know, how to go with this.</p>