Damping is used to reduce the physics world velocity of instances, and differs from friction in that friction only occurs when two instances with fixtures are in contact. 模拟阻尼比摩擦要容易得多，但请注意，阻尼不是摩擦的替代品；这两个效果可以而且应该一起使用。Here is an image to illustrate damping:
Damping parameters should be between 0 and infinity, with 0 meaning no damping, and infinity meaning full damping. Normally you will use a damping value between 0 and 1, but you can use any non-negative value if required.
|fixture||the index of the fixture|
|damping||the damping of the fixture, usually between 0 and 1|
The code above will set the linear damping of the fixture indexed in "fix_ball" to 0.1.