The actinides are a group of heavy, radioactive metals. This group includes elements like uranium, plutonium, and thorium. Because of their radioactivity, you will not find actinides in a standard auto shop or passenger car. However, they are studied in advanced nuclear engineering and aerospace design.
In specialized military and space vehicles, depleted uranium (an actinide) is used for its extreme density. It is used as counterweights in aircraft controls and as heavy armor plating on military transport vehicles. Its density makes it highly effective at absorbing kinetic energy from impacts.
Understanding these heavy metals also drives research in radiation shielding. Engineers designing deep-space probes use lead and other dense metals to protect electronics from cosmic radiation. The materials science learned from shielding actinides helps improve civilian safety systems.