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I have issue regarding speed in air. When i jump and move simultaneously that time speed of player increase.For jump i am using impuls and for movement i am using force.I want to slow speed when player is in air.

Thanks in advance

Following is my update method ih HUDLayer

-(void)update:(ccTime)dt :(b2Body *)ballBody :(CCSprite *)player1 :(b2World *)world

    if ( 
        b2Vec2 locationworld=b2Vec2(maxSpeed,0);
        double mass=ballBody->GetMass();
        ballBody->ApplyForce(mass*locationworld, ballBody->GetWorldCenter());
      //  ballBody->SetLinearDamping(1.2f);
    else if(
        b2Vec2 locationworld=b2Vec2(-10,0);
        double mass=ballBody->GetMass();
        ballBody->ApplyForce(mass*locationworld, ballBody->GetWorldCenter());
    //    ballBody->SetLinearDamping(1.2f);


} Following is jump

    if (touch) 

        if ( 
            b2Vec2 locationWorld;
//        double mass=ballBody->GetMass();
            ballBody->ApplyLinearImpulse(locationWorld, ballBody->GetWorldCenter());
      //  ballBody->ApplyForce(mass*locationWorld, ballBody->GetWorldCenter());


So where i apply logic??

share|improve this question Perhaps this can help? – Sidar Sep 5 '12 at 6:37
Inertia makes it harder to change velocity. It will not slow the player down which I believe is what the OP is asking for. – ClassicThunder Sep 5 '12 at 6:56
Yes i am trying ballBody->SetLinearDamping(1.2f); but can not see any effect. – Diken Sep 5 '12 at 7:06
Well that is a ridiculously huge value for linear damping. "Normally you will use a damping value between 0 and 0.1." You should keep this handy – ClassicThunder Sep 5 '12 at 7:14
up vote 4 down vote accepted

Sounds like you want a friction joint. Set the two anchor points to zero so the friction doesn't have any direction. Below is vague pseudocode of how to create a friction joint and add it to your world.

Also make sure you keep the Box2D Manual handy.

var frictionJoint = new FrictionJoint();

frictionJoint.localAnchorA = new Vector2(0,0);
frictionJoint.localAnchorB = new Vector2(0,0);

frictionJoint.bodyA = yourBall;
frictionJoint.bodyB = ASquareAsLargeAsTheAreaYouNeedFrictionIn

frictionJoint.maxForce = 0.5; //This the most force the joint will apply to your object. The faster its moving the more force applied
frictionJoint.maxTorque = 5; //Set to 0 to prevent rotation

share|improve this answer
How to add friction joint and which anchor point i have to set to zero?? – Diken Sep 5 '12 at 7:05
@Diken updated answer – ClassicThunder Sep 5 '12 at 7:12
This code is apply in update method of I show you my code of jump and movement of player – Diken Sep 5 '12 at 7:16
No just once after you create the two necessary bodies. – ClassicThunder Sep 5 '12 at 7:20
But player is a dynamic body and which is define in your code as yourBall but what about bodyB?? – Diken Sep 5 '12 at 7:25

Unlike surface friction between solids, air friction (drag) depends on the speed of the object, squared.

An easy way to model friction and drag

F(friction) = -k;
F(drag) = speed * speed * -k;

Both forces act in the opposite direction to the velocity of the object.

Notice that surface friction is a constant whereas air friction (drag) must be modified each frame according to the object speed (length of velocity vector)

share|improve this answer

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