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In the manga [Mudazumo Naki
Kaikaku](https://en.wikipedia.org/wiki/Mudazumo_Naki_Kaikaku), the protagonist
Junichiro Koizumi is able to use "goumoupai", the ability to turn any mahjong
tile into a white/haku tile simply by _gripping it with immense strength_ ,
usually leaving the tile dented.

Sure, the manga frequently goes overboard with the abilities of each
character, but this one seems like it might actually be possible in real life.
I'd assume that the [material the tile is made out
of](http://www.sloperama.com/majexchange/id.html) would be a giant factor, but
apparently Koizumi can even do it with _depleted uranium tiles_.

How much grip force would be needed to scrape/dent a mahjong tile so that it
turns white? Would it be possible for a human (for any material)?


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question
mudazumo-naki-kaikaku
Is it physically possible to turn a mahjong tile white with a super grip?


The average human hand cannot produce enough grip force to do such a thing. In
[this study on grip strength](http://www.bleng.com/rfv-22.aspx), the maximum
key grip (holding an object like you would a key) force listed is 42 pounds.

Wood will probably be the softest material a typical modern mahjong tile is
made of, from the link in your post. Looking at the [compression strength
properties of
wood](http://www.gutenberg.org/files/12299/12299-h/12299-h.htm#I_04), the
softest wood listed compresses at 193 pounds per square inch. Keep in mind
that hardwoods like maple (456 psi) or oak (778 psi) would actually be used
rather than softwoods.

Plastics take things to an entirely new level. [This
chart](http://www.matweb.com/reference/compressivestrength.aspx) shows the
compressive properties of some common polymer plastics. Note that the values
are given in MPa, or megapascals. 1 megapascal = 145.037738 pound-force/square
inch (PSI).

As for materials such as pulverized bone, the only references I could find
involved using the materials as partial replacement for concrete. I'd say it's
safe to infer that the compressive strength for the compound used in making
mahjong tiles would be at least as strong as hardwoods.

Keep in mind these figures only talk about the compression strength of the
material. Just compressing the tile alone would not be enough to remove the
engraving and paint of the characters on the tile face. Some shear force would
also need to be applied as well. I don't think it's necessary to go there at
this point, though.


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answer