For thousands of years, boats have been a critical component of trade, efficiently enabling transport of goods over large distances. But water’s self-leveling creates challenges when moving up and downstream through rivers and canals. To get around this, engineers use locks, which act as a sort of gravity-driven elevator to lift and lower boats to the appropriate water level. In this video from Practical Engineering, we learn about the basic physics behind locks as well as some of the methods engineers use to limit water loss through the lock. (Image and video credit: Practical Engineering)