There is an article "Physics of the Kick Serve" by Rod Cross. On TW forum webpage click "Improve" then "Tennis Warehouse University" to find a link to the article. This used to work in the past. When I click "Improve" and then "Tennis Warehouse University" it says server not found. "Firefox can't find the server at twu.warehousesports.lan." Some of the other links that I tried on that "Improve" webpage work OK. If I search for the article through Google I get a link that works, no trouble. http://twu.tennis-warehouse.com/learning_center/kickserve.php 8/22/2016 -- I just updated my Firefox to version 48.0.1 and similar result.