Sprite Entity keeps falling

I keep wondering why the sprite keeps falling whenever I move the car sprite. I already added a collision component for this, and here is what the setting looks like:

image

Is there anything else that I could do?

CarControl.prototype.update = function (dt) {
    if (this.app.keyboard.isPressed(pc.KEY_UP)) {
        this.entity.sprite.play("CarMoving");
        this.entity.rigidbody.applyForce(0, 20, 0);
    }
    else if (this.app.keyboard.isPressed(pc.KEY_RIGHT)) {
        this.entity.rigidbody.applyForce(20, 0, 0);
    }
    else if (this.app.keyboard.isPressed(pc.KEY_LEFT)) {
        this.entity.rigidbody.applyForce(-20, 0, 0);
    }

};

Have you got gravity set in the world? ie Are they falling?