A group is defined as a collection of individuals engaging in face to face interaction and sharing a common fate. The face to face interaction aspect of definition of groups places limits on size. You can only get so big and still have face to face contact, which includes an awareness that members have of each other. Cohesiveness is defined as all of the forces pulling group members together, such as members' liking for one another as well as the rewards and benefits resulting from group membership. Higher cohesiveness is associated with increased conformity to group norms.
Groups influence their members in many important ways.
The effects of groups can be varied and complex. One of the simplest ways that groups can influence individuals is through the sheer fact of their presence. The most basic effects of a group stem from the fact that people are physically present when you are in a group. Imagine that you are riding a bicycle around a race track. Early research by Triplett involved motor tasks like bicycling and winding fishing reels, employing a co-action manipulation.