On the islands of Sicily lies the historic city of Syracuse, which is noted for its rich Greek and Roman history, culture, and architecture. This place is also famous for being the birthplace of the preeminent astronomer, inventor, engineer, mathematician, and physicist - Archimedes. In the third century BC, the ruler of Syracuse, King Heiron, was presented with a crown supposedly made of pure gold. He was quite suspicious about the authenticity of the craftmanship. It was not uncommon for goldsmiths to adulterate gold with cheaper metals such as silver or copper. The king wanted to test it and turned to his advisors, but none accomplished the task. The major problem was that a non-destructive method had to be used, as the crown held religious importance, in addition to being a magnificent work of art. This is where Archimedes' enters the story, and this task led to Archimedes’ best-known achievement - the discovery of the principle of buoyancy, which he did while bathing in a public bathhouse. He was immensely excited by his discovery that he leapt from the bathtub and ran through the streets, still wet and naked, yelling, “Eureka! Eureka!”. His test worked, and he proved that the crown was not pure gold.
The Archimedes’ Principle is defined by the Encylopedia Britannica as “Any body completely or partially submerged in a fluid at rest is acted upon by an upward buoyant force, the magnitude of which is equal to the weight of the fluid displaced by the body. The volume of the displaced fluid is equal to the submerged volume of the object, and the weight of the displaced fluid is equal to the magnitude of the buoyant force.”
In the Central Lowlands of Scotland, to the Northwest of Edinburgh and Northeast of Glasgow, lies a large town named Falkirk. It was a town of great significance during the Industrial Revolution due to its key location on the transportation route. It grew up to be a heavy-industry centre being the junction of the Forth and Clyde and Union Canals. What is so interesting about Falkirk is that the canals have an altitude difference of several tens of meters, and yet boats navigate the waters. Doesn’t this make you ponder about how the boats gain or lose elevation?
It is easy to imagine a car gaining height on the road by climbing bridges or overpasses (flyovers), or even trains climbing hills in a spiral or zig-zag path along the mountainside. However, when it comes to waterways, things become a bit hazy. One cannot imagine a boat climbing upstream in a canal, given that any incline will cause the water to flow downhill and flood the lower levels. It is quite stupefying to know that boats, like humans, use elevators, lifts, escalators and even (water) staircase to climb up and down. Boat lift or lift-lock, canal lock, and canal inclined-plane are the various mechanisms employed to transport boats between water at two different elevations.
How would you feel if you had to spend all day climbing a flight of stairs (of water) with just 11 steps? Bored? That was the fate of the boats that wished to traverse across the two canals until the 1930s. Since 2002, boats are transported between the low lying Forth and Clyde Canal and the elevated Union Canal by the only rotating boat lift in the world - Falkirk Wheel. The Wheel has two opposing arms whose shape is inspired by a Celtic double-headed battle axe. The two canals are separated by a height of 35m, while the Wheel can raise the boats by just 24 metres. The traversing of the 11 metres difference between the aqueduct and the canal brings us to the most common water navigation structure, the water staircase or Locks, which will be described in Part 2.
Credits: Wikimedia
The Wheel employs two caissons, giant pods filled with water, on which the boats that are to be lifted or lowered are parked. The two caissons are located on either end of the arms and are filled with 500 tonnes of water. Raising a 500-tonne massive object by 24 metres requires a humongous amount of energy - 33 kWh per lift. To throw some perspective, the daily per capita electricity consumption by Indians in 2019 was about 3.3 kWh. By simultaneously making another 500 tonnes of water descend the same height at the same rate, the engineers have brilliantly lowered the consumption to about 1.5 kWh per lift.
From Archimedes' principle, we can understand that when a boat parks itself inside the caisson, it must release an amount of water equal to its weight. Thus, the caisson's weight effectively remains the same at 500 tonnes irrespective of the weight of the boat that is being transported. This phenomenon also enables us to transport a boat in either direction simultaneously. By slightly reducing the rising caisson's weight, we can exploit gravity to rotate the wheel and apply the brakes.
It is quite mesmerising to watch the Falkirk Wheel in action, isn't it? No wonder it has marked its place in history as one of the modern engineering marvels.