LibGDX applyLinearImpulse正在尝试实现Gravity....Confused

World world = new World(new Vector2(0, -9.8f), true);

BodyDef bodyDef = new BodyDef();
bodyDef.type = BodyType.DynamicBody;
bodyDef.position.set(x, y); // 设置物体的初始位置
Body body = world.createBody(bodyDef);

// 创建物体的形状
PolygonShape shape = new PolygonShape();
shape.setAsBox(width / 2, height / 2); // 设置物体的宽度和高度

// 创建物体的夹具（fixture）
FixtureDef fixtureDef = new FixtureDef();
fixtureDef.shape = shape;
fixtureDef.density = 1.0f; // 设置物体的密度

// 将夹具添加到物体中
body.createFixture(fixtureDef);

// 释放形状的资源
shape.dispose();

float timeStep = 1.0f / 60.0f; // 更新的时间步长
int velocityIterations = 6; // 速度迭代次数
int positionIterations = 2; // 位置迭代次数

world.step(timeStep, velocityIterations, positionIterations);

float gravityForce = 9.8f; // 重力的大小
Vector2 gravity = new Vector2(0, -gravityForce); // 重力向量

body.applyLinearImpulse(gravity, body.getWorldCenter(), true);