title: make physics body jump in cocos2d-Box2d
body: <p>I am a newbie to the gaming world i am stuccoed to make a physics body jump..<br>
  here is how i defined the body</p>
  
  <pre><code>Cycle = [CCSprite spriteWithFile:@"Panda.png"];
          [self addChild:Cycle z:3];
  
      // Create a world
      b2Vec2 gravity = b2Vec2(0.0f, -8.0f);
      world = new b2World(gravity);
  
      // Create edges around the entire screen
      b2BodyDef groundBodyDef;
      groundBodyDef.position.Set(0,0);
  
      b2Body *groundBody = world-&gt;CreateBody(&amp;groundBodyDef);
      b2EdgeShape groundEdge;
      b2FixtureDef boxShapeDef;
      boxShapeDef.shape = &amp;groundEdge;
  
      //wall definitions
      groundEdge.Set(b2Vec2(0,0), b2Vec2(screenSize.width/PTM_RATIO, 0));
      groundBody-&gt;CreateFixture(&amp;boxShapeDef);
  
      groundEdge.Set(b2Vec2(0,0), b2Vec2(0,screenSize.height/PTM_RATIO));
      groundBody-&gt;CreateFixture(&amp;boxShapeDef);
  
      groundEdge.Set(b2Vec2(0, screenSize.height/PTM_RATIO),
                     b2Vec2(screenSize.width/PTM_RATIO, screenSize.height/PTM_RATIO));
      groundBody-&gt;CreateFixture(&amp;boxShapeDef);
  
      groundEdge.Set(b2Vec2(screenSize.width/PTM_RATIO, screenSize.height/PTM_RATIO),
                     b2Vec2(screenSize.width/PTM_RATIO, 0));
      groundBody-&gt;CreateFixture(&amp;boxShapeDef);
  
      // Create ball body and shape
      b2BodyDef ballBodyDef;
      ballBodyDef.type = b2_dynamicBody;
      ballBodyDef.position.Set(300/PTM_RATIO,100/PTM_RATIO);
      ballBodyDef.userData = Cycle;
      body = world-&gt;CreateBody(&amp;ballBodyDef);
  
  
      b2PolygonShape dynamicBox;
      dynamicBox.SetAsBox(.5f, .5f);//These are mid points for our 1m box
  
      // Define the dynamic body fixture.
      b2FixtureDef fixtureDef;
      fixtureDef.shape = &amp;dynamicBox;
      fixtureDef.density = 1.0f;
      fixtureDef.friction = 0.3f;
      body-&gt;CreateFixture(&amp;fixtureDef);
  </code></pre>
  
  <p>and in touches began i am applying linear impulse as</p>
  
  <pre><code>b2Vec2 force = b2Vec2(30, 30);
  body-&gt; ApplyLinearImpulse(body-&gt;GetPosition(),force);
  </code></pre>
  
  <p>so can any body tell me what am i doing wrong..<br>
  thanks in advance..</p>