The 3D Graphics API was added in the recently released Silverlight 5 Beta. Having 3D graphics support is a major advancement in Silverlight and is expected to have a huge impact in the near future.
One are where the 3D Graphics API can be useful is 3D Graphics
3D Physics demo
There are a lot of places that you can visit to gain more knowledge about the 3D Physics.
Here are some useful links: