Harley-Davidson XA Into the war, the government asked Harley to build a bike that was similar to the BMWs used by the Germans. So they didâto exacting specification. The 740cc flat twin and shaft drive aped the R71 perfectly. Harley built 1,000 XAs and even used the platform to test its first telescoping fork.
Definition of atom for English Language Learners. : 1  the smallest particle of a substance that can exist by itself or be combined with other atoms to form a molecule. : 2  a very small amount of something.
The atomic number is the number of protons in an atom. This number is fixed and determines what element that atom is. The atomic mass is the mass of an atom and is roughly equâ¦ivalent to the number of protons plus the average number of neutrons that atoms of that particular element.