Uphill Water — How does a canal lock work, and how does a boat go up a hill?

A canal lock is a stone box with a gate at each end: you shut the boat inside, let water in until the level rises, and the boat floats up the hill. Nothing lifts the boat — the water under it is raised instead, which is why the same trick works on a 50,000-tonne ship. In this lesson you work the gates and the paddles yourself: ride your own boat four metres down a wall, lift it back up through a real lock, and then take it down again without draining the canal on the boat moored above you.