cocos2d-iphone - cocos2d box2d : different mass but body fall at same time

Question

我用 cocos2d sprite 创建了 2 个 box2d body ……它们有不同的质量，它们从世界上的同一个地方掉下来。但他们同时倒地。我的想法是，较轻的 body 应该比较重的 body 晚一点……但他们没有。

for (int k=1;k<=2; k++) {
    int idx = (CCRANDOM_0_1() > .5 ? 0:1);
    int idy = (CCRANDOM_0_1() > .5 ? 0:1);
    CCSprite *sprite = [CCSprite spriteWithBatchNode:batch rect:CGRectMake(32 * idx,32 * idy,32,32)];
    [batch addChild:sprite];

    sprite.position = ccp( p.x+(32*k), p.y);


    b2BodyDef bodyDef;
    bodyDef.type = b2_dynamicBody;

    bodyDef.position.Set(( p.x+(32*k))/PTM_RATIO, p.y/PTM_RATIO);
    bodyDef.userData = sprite;

    b2Body *body = world->CreateBody(&bodyDef);


    b2PolygonShape dynamicBox;
    dynamicBox.SetAsBox(.5f, .5f);//These are mid points for our 1m box


    b2FixtureDef fixtureDef;
    fixtureDef.shape = &dynamicBox; 
    fixtureDef.density = 1.0f/k;
    fixtureDef.friction = 0.3f;
    body->CreateFixture(&fixtureDef);
    NSLog(@"%f",body->GetMass());
}

Answer 1

好吧，伽利略伽利莱发现所有物体都以相同的速度下落......

https://web.archive.org/web/20100728100438/http://galitzin.mines.edu/INTROGP/notes_template.jsp?url=GRAV%2FNOTES%2Ffallb.html&page=Gravity%3A%20Notes%3A%20Falling%20Bodies