Final answer:
Special interest groups focus on influencing specific policies within the political system to benefit their narrow interests, whereas social movements aim for widespread social change, which can have a global impact.
Step-by-step explanation:
The major difference between a social movement and a special interest group is that special interest groups are smaller entities that work within the political system to influence specific public policies, often representing narrow objectives, while social movements are broad coalitions that strive for larger social change and may work both inside and outside formal political channels.
Special interest groups may lobby legislators intensely to enact or prevent policies that affect their particular interests, even when those policies may not be in the broader public's best interest. Conversely, social movements are organized groups aiming for social goals that often reflect a wider public concern and can lead to transformative change in society, tackling issues from anti-tobacco legislation to global political uprisings.