> ... Centrifuges allow scientists to separate the two uranium isotopes because the heavier isotope—uranium-238—is pushed to the outside of the rapidly spinning

> ... Centrifuges allow scientists to separate the two uranium isotopes because the heavier isotope—uranium-238—is pushed to the outside of the rapidly spinning machine while the uranium-235 clusters in the middle. By repeating this process over and over again, scientists can push concentrations of uranium-235 from less than 1 percent to above 90 percent. It's worth mentioning that the centrifuge operates on a gaseous form of uranium: UF6. As the centrifuge spins, the slightly lower density of 235-UF6 relative to 238-UF6 causes the former to remain toward the center of the centrifuge with the latter drawn toward the outside. https://en.wikipedia.org/wiki/Zippe-type_centrifuge#Centrifuge_uranium_enrichment https://en.wikipedia.org/wiki/Zippe-type_centrifuge#Centrifu... The hard part is that the centrifuge must be spun at very high speed (90,000 RPM), or close to mach 2 linear velocity. The materials and manufacture must be top quality to withstand the forces involved. It's also worth pointing out that this sensitivity was exploited by Stuxnet - a US-developed cyber attack that caused Iran's centrifuges to disable certain protocols that prevented damage during the high-RPM spinning. https://en.wikipedia.org/wiki/Stuxnet https://en.wikipedia.org/wiki/Stuxnet