This lecture covers the core concepts of computational cell biology, focusing on forces and compartments within cells. It discusses direct forces such as gravitational and Coulomb forces, as well as indirect forces like hydrophobic effects and fluctuation-induced forces. The limitations of direct forces in cells are explored, highlighting the importance of indirect forces mediated by the environment. The lecture also delves into the formation of membraneless organelles, the hydrophobic effect, and the role of compartments in spatial segregation of cellular functions.