Critical Mass
http://andrewchen.co/social-network-marketing-getting-from-zero-to-critical-mass/
This article discusses critical mass and how once a product reaches a certain number of users, it will begin to expand rapidly. It points out that the point of “critical mass” is different and varies based on the situation. For example, the critical mass of Skype is only 2 people, while a forum needs around 10 and a social network will probably need a lot more than that. If you are marketing your product, you need to get a) the right people to join, and b) get enough people to reach your specific critical mass. A good example given is Facebook. The social network could thrive with a reasonably small critical mass within a given college. Once they had enough small systems (colleges), they had reached a different, and larger, critical mass for public use, and it exploded when opened to the public.
This is very similar to the stable and unstable equilibrium points we have been discussing in class. When the value exceeds the price, people will continue buying/using the object until it reaches the stable equilibrium. It also shows, however, that a simple formula is certainly not accurate in describing how a product spreads based on usage. For example, there might be two unstable equilibria with stable equilibria between the two – as in the case for Facebook. Every case is different, but the mathematical model gives an estimate of what is actually happening.