<P> A closed system is a physical system that does not allow certain types of transfers (such as transfer of mass and energy transfer) in or out of the system . The specification of what types of transfers are excluded varies in the closed systems of physics, chemistry or engineering . </P> <P> In nonrelativistic classical mechanics, a closed system is a physical system that doesn't exchange any matter with its surroundings, and isn't subject to any net force whose source is external to the system . A closed system in classical mechanics would be considered an isolated system in thermodynamics . Closed systems are often used to limit the factors that can affect the results of specific problem or experiment . </P>

The earth is a closed system. what does this mean