Social movement: organized activity that encourages or discourages social change spontaneous, and usually in violation of established norms rumour, public opinion, fashion and fads and panic and mass hysteria. Collective behaviour : activity involving large number of people, often. Other forms of collective behaviour includes mobs, riots, crowds, gossips and: studying collective behaviour is difficult for three reasons: Localized collectivities: crowds crowd: temporary gathering of people who share a common focus of attention and who influence one another. Mobs and riots: defn: loose collection of people who interact very little, if at all, ex. People lying on a beach: defn: results from deliberate planning, ex. Crowds, mobs, and social change: ordinary people can gain power by acting collectively, power of the crowd to challenge the status quo and sometimes to force social change is the reason that crowds are controversial.