cocos2d-x3.0使用物理引擎做了一个球，模拟抛向空中，然后掉回到地面，整个过程动画很慢。怎么办法让整体动画快点？是减小空气阻力，还是设置重力参数？附上代码：
Scene* HelloWorld::createScene()
{
auto scene = Scene::createWithPhysics();
auto layer = HelloWorld::create();
layer->setPhyWorld(scene->getPhysicsWorld());
scene->addChild(layer);
return scene;
}
bool HelloWorld::init()
{
if (!Layer::init()) {
return false;
}
auto visibleSize = Director::getInstance()->getVisibleSize();
auto origin = Director::getInstance()->getVisibleOrigin();
_ball = Sprite::create("Coin.png");
_ball->setPosition(Point(visibleSize.width/4, (visibleSize.height/4)*3));
auto ballBody = PhysicsBody::createCircle(_ball->getContentSize().width /2);
ballBody->setVelocity(Vect(50.0f, 150.0f)); //设置一个方向点
ballBody->setDynamic(true);
ballBody->setGravityEnable(true);
_ball->setPhysicsBody(ballBody);
this->addChild(_ball);
return true;
｝
