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I was surprised to learn about gauge blocks and how you stick them together. The blocks have very smooth surfaces and still they stick by wringing ( https://youtu.be/2lOOl3VxOtE ).

One speaks of molecular binding (van der Waals?), vacuum and air pressure (even Casimir effect, which I doubt), oily stuff, or maybe other things. There is no magnetism involved. I can't imagine a vacuum is induced by wringing. It's a curious case. What happens?

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    $\begingroup$ en.wikipedia.org/wiki/Gauge_block has some discussion. $\endgroup$
    – Jon Custer
    Commented Apr 6, 2022 at 14:32
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    $\begingroup$ Note that the Wikipedia article says that "the exact mechanism that causes wringing is unknown", so you may not get a better answer here. $\endgroup$
    – Michael Seifert
    Commented Apr 6, 2022 at 14:33
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    $\begingroup$ I have felt "Jo" blocks "stick" together; never understood. Not magnetism, not oil. $\endgroup$
    – blacksmith37
    Commented Apr 6, 2022 at 14:46
  • $\begingroup$ @blacksmith37 - on very smooth surfaces, the adsorbed species (primarily water) can be thick enough to provide a lot of surface tension. Further, that 'liquid' is attached quite well to the surfaces, and is thin enough that significant shear forces can be neutralized. $\endgroup$
    – Jon Custer
    Commented Apr 6, 2022 at 15:32

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There are at least two effects at work here, as follows.

Because the gauge blocks are optically flat (very flat indeed) it is possible to squeeze them together hard enough to form a few metallic bonds between the blocks. The other effect is that once they have been squeezed together hard enough to press out the air trapped between them, air must be re-admitted into the space between them in order to pull them apart once again- and the finite viscosity of the air makes this hard to do.

Note that the "vacuum weld" phenomenon was discovered when satellites were first shot into orbit and it was discovered that their antennae, solar cell wings, etc. failed to unfurl upon command. Tests on the ground revealed that in a vacuum, the metal-to-metal contact in the unfurling mechanisms caused them to jam and get stuck.

BTW this problem could not be cured through the use of silicone-based "vacuum grease" because those silicone-based lubricants showed a marked tendency to diffuse out across surfaces in a vacuum, which then fouled the sensors and lenses on the satellites.

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we have a similar event that happens in pneumatics and hydraulics. if i have a piston flat up against the gland. the piston holds on to the gland until there is enough force to suck in air/fluid between the 2 parts to seperate them... we overcome this issue by purposely machining in undercuts or spirals on the faces to let in air/fluid with less force.

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