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TEST 144 READING PASSAGE 2
You should spend about 20 minutes on
Questions 20-26
which are based on
Reading Passage 2 below.
[Note: This is an extract from READING PASSAGE 2 about The Falkirk Wheel]
A unique engineering achievement
The Wheel consists of two sets
of opposing axe-shaped arms, attached about
25 metres apart to a fixed central spine. Two diametrically opposed water-filled
‘gondolas’, each with a capacity of 360,000 litres, are fitted between the ends of
the arms. These gondolas always weigh the same, whether or not they are carrying
boats. This is because, according to Archimedes’ principle of displacement, floating
objects displace their own weight in water. So
when a boat enters a gondola,
the amount of water leaving the gondola weighs exactly the same as the boat.
This keeps the Wheel balanced and so, despite its enormous mass, it rotates
through 180° in five and a half minutes while using very little power. It takes just
1.5 kilowatt-hours (5.4 MJ) of energy to rotate the Wheel -roughly the same as
boiling eight small domestic kettles of water.
Boats needing to be lifted up enter the canal basin at the level of the Forth & Clyde
Canal and then enter the lower gondola of the Wheel. Two
hydraulic steel gates
are raised, so as to seal the gondola off from the water in the canal basin. The
water between the gates is then pumped out. A hydraulic clamp, which prevents
the arms of the Wheel moving while the gondola is docked, is removed,
allowing
the Wheel to turn. In the central machine room an array of ten hydraulic motors
then begins to rotate the central axle. The axle connects to the outer arms of the
Wheel, which begin to rotate at a speed of 1/8 of a revolution per minute. As the
wheel rotates, the gondolas are kept in the upright position by a simple gearing
system. Two eight-metre-wide cogs orbit a fixed
inner cog of the same width,
connected by two smaller cogs travelling in the opposite direction to the outer
cogs – so ensuring that the gondolas always remain level. When the gondola
reaches the top, the boat passes straight onto the aqueduct situated 24 metres
above the canal basin.
The remaining 11 metres of lift needed to reach the
Union Canal is achieved by
means of a pair of locks. The Wheel could not be constructed to elevate boats
over the full 35-metre difference between the two canals, owing to the presence
of the historically important Antonine Wall, which was built by the Romans in the
second century AD. Boats travel under this wall via a tunnel, then through the
locks, and finally on to the Union Canal.
