This lecture explores the concept of buoyancy in swimming by analyzing the trade-off between power consumption and speed when an object, like a duck, partially emerges from the water. The instructors present a model based on the duck's propulsion system and discuss the optimization of power consumption for maximum speed, considering different scenarios such as multiple independent motors, realistic shapes, variable density, and the use of foils. Through calculations and simulations, they demonstrate the importance of minimizing drag and power consumption to achieve optimal swimming performance.