Python3 packages installation

[Rich Shepard]

   Here, both python-2.7.15 and python3-3.6.6 are installed. Using pip (which
I understand works with both python versions) I was able to install ipython, 
matplotlib, numpy, and pandas. They're all in
/usr/lib64/python2.7/site-packages.

   Now I want to install the same packages for python3 so they are are found
also in /usr/lib64/python3.6/site-packages. I've not found the proper
command line syntax to do this.

   When I try, for example, 'python3 -m pip install numpy3' the system tells
me that pip is not available. I want to learn how to manage both series
since some of the applications I regularly use require python2 while any
python scripts I now write use python3.

   If there's a document or web site that explains how to manage both
versions please point me to it.

Rich