A chain reaction is a process where a single event triggers a series of related events. This concept is commonly seen in nuclear physics, where the splitting of an atomic nucleus, such as in uranium, releases energy and additional neutrons. These neutrons can then cause other nuclei to split, leading to a rapid increase in energy release. Chain reactions can also occur in chemistry, such as in combustion. When a fuel, like gasoline, ignites, it produces heat and light, which can ignite nearby fuel molecules. This process continues as long as there is enough fuel and oxygen, resulting in a sustained reaction.