Making Git untrack few folders

Hi All,

I have couple of interconnected questions:

1. Is there a way I can make Git not track a particular folder in my
working code base directory. For example, I have a tmp folder in my
local code base and I don't want Git to track whats going on inside
that directory.

2. Accidently I have added this folder, committed and pushed it to
origin master. Is there a way I can remove this tmp folder from git
revision history and at the same time keeping it intact in my local
code base directory.

Cheers,
Parag