"real world" restitution and friction values ?

ChrisC · Post by **ChrisC** » Mon Dec 04, 2006 10:18 am

What sort of values would I have to use for friction and restitution, given these examples

friction of:

polished flat metal on ice
unpolished wood on ice
coarse sandpaper on ice
girlfriend spotting I haven't done the washing up

restitution of:

hard cold solid rubber ball on concrete
bouncy inflated warm ball on concrete
inflated ball on earth
inflated ball on lush grass
doing the cooking and washing up when its not my turn

Andrey Tuganov · Post by **Andrey Tuganov** » Fri Jan 12, 2007 6:28 pm

Try this source:
http://www.roymech.co.uk/Useful_Tables/ ... _frict.htm

As for restitution, it?s a touchy thing, strongly dependent on circumstances.

Shaba1 · Post by **Shaba1** » Wed Jan 24, 2007 10:07 pm

What EXACTLY is resistitution. I read that word in the original ketji manual years ago and STILL do not know what the heck it is.

Andrey Tuganov · Post by **Andrey Tuganov** » Mon Jan 29, 2007 9:16 pm

There are some hypotheses which describe how to treat a collision of rigid bodies. For example one says that |normal velocity after impact|=e*|normal velocity before impact|. Another one says that collision includes two phases: compression and decompression. And |normal impulse on decompression phase|=e*|normal impulse on compression phase|. The very coefficient e is called restitution.

Shaba1 · Post by **Shaba1** » Wed Jan 31, 2007 1:47 am

[quote="Andrey Tuganov"]There are some hypotheses which describe how to treat a collision of rigid bodies. For example one says that |normal velocity after impact|=e*|normal velocity before impact|. Another one says that collision includes two phases: compression and decompression. And |normal impulse on decompression phase|=e*|normal impulse on compression phase|. The very coefficient e is called restitution.[/quote]

Thank you Andrey. Erwin sent me a private message that explained it in a lot more simple terms. Basically he said it was a measure of a material's "bounciness" Zero restitution is equal to no bouciness at all and restitution of 1 means perfect preservation of energy or full bouciness. For those of us for whom physics classes were a thing of the 1970s this makes a lot more sense.

Andrey Tuganov · Post by **Andrey Tuganov** » Wed Jan 31, 2007 7:28 pm

Well, sorry. I keep the things strict, and I can't call it bounciness of material. It isn't a property of material.

Andrey Tuganov · Post by **Andrey Tuganov** » Wed Jan 31, 2007 9:16 pm

And that is exactly why the restitution table is not to be found.