This lecture introduces the fundamentals of fluid dynamics as they relate to sediment transport in natural environments like rivers and oceans. Prof. Southard explains key concepts such as laminar versus turbulent flow, Reynolds number, and dimensional analysis, using classic experiments to illustrate how fluid behavior changes with velocity. The discussion then expands to forces acting on particles, including drag, lift, and the role of viscosity, as well as how flow interacts with boundaries in channels. The lecture also explores oscillatory flows generated by waves, their effects on sediment movement, and how combined flow conditions can become complex. Finally, it examines how sediment begins to move, highlighting factors like shear stress, particle size, and turbulence, and introduces concepts such as the Shields diagram to describe the onset of motion.