Final answer:
Stimulus diffusion is where part of a culture or concept is adopted by another group and altered, as in the case of hip hop music's evolution from New York to New Jersey and Los Angeles. The idea spreads, but modifications are made to fit local preferences or conditions, which is a key aspect of cultural expansion diffusion.
Step-by-step explanation:
Stimulus diffusion is a type of cultural diffusion where a specific aspect or innovation of a culture or concept spreads to another culture, but the adopting group modifies or changes it. For example, the hip hop music that originated in New York's Bronx included DJs and MCs but changed form when it spread to New Jersey and incorporated trained musicians. Similarly, when hip hop reached Los Angeles, the style was further altered to adapt to local preferences, leading to the emergence of 'gangsta rap'.
This form of diffusion illustrates how objects or ideas can influence a culture even when the original object or idea does not completely transfer over. Expansion diffusion and relocation diffusion are two primary types of spatial diffusion, with stimulus diffusion falling under the category of expansion diffusion.
In free diffusion, which is an analogous physical process, substances spontaneously move from areas of higher concentration to lower concentration until equilibrium is reached. This natural phenomenon can be observed when food coloring is placed in water and gradually spreads out until evenly dispersed.