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.
(How do atoms form?) What is the biggest atom? The smallest atom? If by biggest and smallest, you mean mass (which is a measure of how much matter is there), then the smallest is the hydrogen atom with one proton and one electron. Since electrons are about 2000 times less massive than protons (and neutrons), then the mass of an atom is mostly from the protons and neutrons.