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Because, you know, stuff
My guess is that the diamond needle is small enough to fit in the records ditch(?), but light enough not to scratch it.
Or maybe you're just playing the wrong record[^]
I'd always thought the greater contributor to the slipperiness of PTFE was it's chemical inertness. I mean, steel is both quite reactive and quite hard, being around 80% as hard as PTFE, but a whole heap more reactive. Teflon is only about 25% harder than steel but is many times more slippery.
Don't suppose you've any idea where I can read more about the mechanism of the PTFE's slipperiness do you?
My response was supposed to be sarcastic. I'm sorry if it wasn't coming through properly.
Pure PTFE has a hardness of 60 Shore D, a bit higher with filler materials. Steel has a hardness ranging from 52 - 65 Rockwell C, where the sheet steel in a can has the lower number and a steel file is around 63 Rockwell C. A high quality chefs knife has about 58 Rockwell C.
But note that it completely different scales that doesn't even compare. 60 Shore D is approximately somewhere between a rubber tyre and nylon in hardness. Steel is many magnitudes harder.
Anyway, friction is pretty complex. There is not one reason for it and it's very many years since I studied it.
At Quora there's a discussion with many links explaining the many reasons behind friction. It's a good place to begin. What causes friction? - Quora[^].