Q: How detergents clean dirty clothes ?
Sol: Water can not remove grease stains . This is because water does not wet a greasy spot . The molecules of a detergents are hair pin shaped , experiencing different amount of forces at the ends due to water molecules and grease molecules . The molecules are as if pinned to small globes of greasy dirt and form an interface between water and greasy dirt globes . The greasy dirt is thus dislodged from the clothes and is carried away with running water .