iMechanica has a search box, but its algorithm is less sophisticated than that of Google.  You may wish to use Google to search content on iMechanica.  For example, if you are looking for friction in iMechanica, type into the Google search box: friction site:imechanica.org

If instead you are only interested in rolling friction, then type into the Google search box: "rolling friction" site:imechanica.org.  The quotation marks ensure that all the included words appear in search results.