Cars do not use rail gun technology for propulsion due to the inefficiency and energy requirements of such systems compared to traditional combustion engines. Liquid fuels provide a higher energy density than electric batteries, enhancing range and economy. While concepts like free-piston engines and linear generators exist, they still rely on efficient energy storage and conversion methods. Electric motors are already highly efficient, with energy storage being the primary limitation. Overall, while railgun-like technologies may have niche applications, they are not practical for mainstream automotive use.