# In Simscape-M​ultibody-C​ontact-For​ces library is there a Face to Face Contact Force Block?

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John O on 3 Aug 2021
Commented: John O on 11 Feb 2022
I am new to Simscape and Multibody contact Forces.
So, I know there is a Face to Plane Contact Force Block, where the plane is assumed to be much larger than the face.
But I need a Face to Face Block, where, in my case, both faces will be identical in size.
Is this available or even possible to create in Simscape?
The simpelest way to look at it is: I need to model two dice sliding on a plane towards each other, where any face on one dice might contact any face on the other die, we can assume at this point that the contacting faces are oriented parallel to each other.
My untimate model would be much more complicated with multiple dodecaherons, rolling at arbitrary angles, but the above will suffice for now.
John

Steve Miller on 24 Aug 2021
Hi John O,
While the Simscape Multibody Contact Forces library could be used for these types of collisions, a better solution would be to use the Spatial Contact Force block that ships with Simscape Multibody. I recommend you attach a Point Cloud block to each die with points representing each of the corners. Between each pair of dice (die A and die B) place two Spatial Contact Force blocks. One Spatial Contact Force block will connect to the Point Cloud on die A and the exported geometry on die B, the other will connect to the Point Cloud on die B and the exported geometry on die A.
--Steve
Steve Miller on 11 Feb 2022
Hi John - attached is a function I created to create point clouds for bricks. See if it helps you. If you want to measure the distance between the two solids, you can use another Spatial Contact Force block attached to the solids, but set the stiffness to 0. This won't give you the force, but it will give you the separation distance.
--Steve
John O on 11 Feb 2022
Thank you Steve, I'm looking at that now.
And just in general, will using point clouds result in a simulation performance improvement over just using the two solid's geometries with a Spatial Contact Force block?
Or maybe a more general question is what is the advantage of the Point Cloud blocks?
I have been experimenting with PCB's in my simulation and it seems to be behaving pretty much the same, Though of course I may not be implementing them optimally!
~John

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