# Modified Hertz Model - C++ **URL:** \ **Category:** PFC\ **Tags:** faq\ **Created:** [April 1, 2023, 8:07pm UTC](https://forum.itascainternational.com/t/modified-hertz-model-c/982 "2023-04-01T20:07:29Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![awbrandt](https://avatars.discourse-cdn.com/v4/letter/a/cdc98d/32.png) [@awbrandt](https://forum.itascainternational.com/u/awbrandt)\ **Post date:** [April 1, 2023, 8:07pm UTC](https://forum.itascainternational.com/t/modified-hertz-model-c/982/1 "2023-04-01T20:07:30Z")
I am looking to modify the contactmodelhertz.h and/or contactmodelhertz.cpp in PFC3D to remove the ability of a ball-wall or pebble-wall interface to experience frictional slip (i.e. a clump and a wall will translate together and rotation of the clump is allowed). I am planning on doing this by setting the hz\_slip property to always be false - will this prevent sliding at the contact, or is there another place (or multiple places) that I should be setting the slip behavior to be false (i.e. where is the exact place in the contact model or in the program mechanics code that determines if a contact is sliding)? Is this the correct way to go about inhibiting sliding behavior? I tried setting the friction coefficient to be arbitrarily high, but this did not prevent sliding in my simulation. I also cannot fix the pebble or line of pebbles because I need to allow rotation, and the contacts that need to not be slipping changes depending on the time instance of the wall input motion. Any help is appreciated. ---
**Author:** ![dblanksma](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@dblanksma](https://forum.itascainternational.com/u/dblanksma)\ **Post date:** [April 5, 2023, 2:59pm UTC](https://forum.itascainternational.com/t/modified-hertz-model-c/982/2 "2023-04-05T14:59:44Z")
Hello @awbrandt, I have received your support request at [PFCsupport@itascacg.com](mailto:PFCsupport@itascacg.com) and will start to review your inquiry shortly. Thank you. – Derrick