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.
electron, An elementary particle that orbits the nucleus of an atom. There is one electron for every proton in the nucleus, which keeps the atom electrically neutral, as electrons are considered to have a negative charge and protons a positive charge.lementary particle elementary particles,the most basic physical constituents of the universe. Basic Constituents of Matter Molecules are built up from the atom, which is the basic unit of any chemical element. The atom in turn is made from the proton, neutron, and electron......