Update schedule

It might seem pretty simple. I created a method, and I called it, as shown below, in the init method.

[self createNewSpr:ccp(s.width * 0.25,s.height-200)];
[self createNewSpr:ccp(s.width * 0.50,s.height-200)];
[self createNewSpr:ccp(s.width * 0.75,s.height-200)];
[self scheduleUpdate];

I defined a for loop in my update method, which imposes a higher gravity than the world on sprites. Only the last challenge depends on the new gravity, but the first and second act of world gravity. I'm not sure what is wrong, but I suspect this is scheduleUpdate. Please, help.

Edit: update method:

-(void) update: (ccTime) dt 
{
 int32 velocityIterations = 8;
 int32 positionIterations = 1; 
 world->Step(dt, velocityIterations, positionIterations);
 for (b2Body* b = world->GetBodyList(); b; b = b->GetNext())
   {
     if (b == sprite)
        {
         b->ApplyForce( b2Vec2(0.0,20*b->GetMass()),b->GetWorldCenter());
        }
   }
}

the createNewSpr:
-(void) createNewSpr:(CGPoint)pos {
//CGSize s = [CCDirector sharedDirector].winSize;
b2Vec2 startPos = [self toMeters:pos];
CGFloat linkHeight = 0.24;
CGFloat linkWidth = 0.1;

b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;
bodyDef.position = startPos;
b2FixtureDef fixtureDef;
fixtureDef.density = 0.1;
b2PolygonShape polygonShape;
polygonShape.SetAsBox(linkWidth,linkHeight);
fixtureDef.shape = &polygonShape;


//first
b2Body* link = world->CreateBody( &bodyDef );
link->CreateFixture( &fixtureDef );

PhysicsSprite* segmentSprite = [PhysicsSprite spriteWithFile:@"sg.png"];
[self addChild:segmentSprite];
[segmentSprite setPhysicsBody:link];


b2RevoluteJointDef revoluteJointDef;
revoluteJointDef.localAnchorA.Set( 0,  linkHeight);
revoluteJointDef.localAnchorB.Set( 0, -linkHeight);


for (int i = 0; i < 10; i++) {

    b2Body* newLink = world->CreateBody( &bodyDef );
    newLink->CreateFixture( &fixtureDef );
    PhysicsSprite* segmentSprite = [PhysicsSprite spriteWithFile:@"sg.png"];
    [self addChild:segmentSprite];
    [segmentSprite setPhysicsBody:link];

    revoluteJointDef.bodyA = link;
    revoluteJointDef.bodyB = newLink;
    world->CreateJoint( &revoluteJointDef );

    link = newLink;//next iteration
}

PhysicsSprite* circleBodySprite = [PhysicsSprite spriteWithFile:@"cb.png"];
[self addChild:circleBodySprite z:1];

b2CircleShape circleShape;
circleShape.m_radius = circleBodySprite.contentSize.width/2 / PTM_RATIO;
fixtureDef.shape = &circleShape;
b2Body* chainBase =world->CreateBody( &bodyDef );
chainBase->CreateFixture( &fixtureDef );
[circleBodySprite setPhysicsBody:chainBase];
sprite = chainBase;

revoluteJointDef.bodyA = link;
revoluteJointDef.bodyB = chainBase;


revoluteJointDef.localAnchorA.Set(0,linkWidth);

revoluteJointDef.localAnchorB.Set(0,linkWidth);
world->CreateJoint( &revoluteJointDef );
}