Can the government require you to a wear seat belt while driving?
What is the argument that it can, and what is the argument that it cannot?
How would such seat belt laws differ from the requirement that infants in cars be in car seats?
In a federal system, the central (or federal) government has much more authority. The central government controls more trade policy, and makes decisions about policy areas that involve interactions between states (such as highway systems). It usually has the power to tax independently of the states and to control the money supply. A federal government also usually has its own mechanisms for enforcement. For example, in the USA, the FBI is the primary agency for investigating federal crimes and crimes that occur between or among multiple states. Not to control residents of individual states on who and who does not mandate wearing of seatbelts.
States (or provinces or regions) still set a great deal of policy and law on their own in federal systems, but these policy areas are somewhat more restricted, and the federal government has its own areas of policy in which states cannot intrude. In a federal system, federal laws usually trump state laws when the two are in conflict. For example, a number of states had laws against homosexual acts, but once the United State Supreme Court (a part of the federal government) ruled that such laws violated an assumed right to privacy in the US (federal) Constitution, the state laws became invalid, because they ran afoul of federal protections of citizens. So when a state says that you do not need to wear a seatbelt and the federal government does then it is up to the centralized government to enforce the law of the land.
In a unitary government, power is almost entirely centralized in a national government. Power devolves to local governments only for the sake of convenience (such as garbage collection times or issuing parking tickets). Any local governments that exist hold power...