erg \erg\, n. gr. ? work. physics
   the unit of work or energy in the c. g. s. system, being the
   amount of work done by a dyne working through a distance of
   one centimeter; the amount of energy expended in moving a
   body one centimeter against a force of one dyne 981 dynes
   exert the same force as a one gram mass in the earth's
   gravitational field. one foot pound is equal to 13,560,000
   ergs. the absolute joule is equivalent to 10^7 ergs, which
   are equivalent to 0.2389 gram-calories at 15deg c. see also
   mechanical equivalent of heat under equivalent.
   1913 webster +pjc
see also:
7 mechanical equivalent of heat equivalent 

erg
     n : a cgs unit of work or energy; the work done by a force of
         one dyne acting over a distance of one centimeter