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Superconducting materials enable probing of out-of-contact friction mechanisms.
TRIBOLOGY IS DEFINED AS "THE STUDY OF CONTACTING BODIES IN RELATIVE MOTION," and we generally think of friction as occurring only when two surfaces touch. However, two closely spaced objects still interact, even if they are not in contact. This implies that energy can be dissipated when two closely spaced objects move relative to one another, producing a friction force, and such non-contact friction has indeed been observed.
There are two possible ways in which energy could be dissipated in this non-contact regime. The first is by electronic friction. When two different materials come close to each other, charge Is transferred from one to the other. When they move relative to each other, this charge can fluctuate to produce a fluctuating current. Just as an electric current passing through a resistive wire loses energy to produce heat, when two surfaces move relative to each other, the fluctuating current produced also...