The Leaning Tower of Pisa

The Leaning Tower of Pisa

About the tower

The leaning tower of Pisa is a bell tower for a nearby cathedral in Tuscany, Italy. It is situated behind the Pisa Cathedral. It currently stands 56.67 meters on the high side and 55.86 meters on the lower. Its architects are said to be Diotisalvi and Guglielmo.

The cause of its inclination

The tower took almost 200 years to complete. Its construction was stopped when the tower began to sink during the construction of the second floor in 1178. This was due to the towers foundation- set in weak, unstable soil. Its construction was halted for almost a century in due course. This allowed the soil to settle. Since then numerous efforts have been made to restore the tower to a vertical position. However,  some of these efforts worsened the tilt.

How does it remain standing?

The Leaning tower of Pisa has been leaning for over 800 years! It has lived through many earthquakes, storms and wars. But the big question is HOW? The reason behind this is something called ‘centre of gravity’. Every object has mass and a centre of gravity or mass.

What is Centre of Gravity?

The centre of gravity is that point inside every object where the objects total weight is thought to be concentrated. An object remains standing until the line drawn from its centre of gravity to the ground falls within its base i.e. if the object stands with the line drawn within its base, it will remain standing but if the line crosses the base it will fall (as shown in the image). In the leaning tower of Pisa, the concept of centre of gravity is very important. The centre of gravity in the leaning tower of Pisa sits somewhere below the top of its 4th floor. The constructors made the tower in a banana shape so that the centre of gravity falls little behind the geometric centre of the base. And this allows the tower to lean a little bit more than it could if it was perfectly straight. The tower being almost 14,500 tonnes  worsens the tilt even more. By 1990 the tilt had reached 5.5°, but the structure was stabilised by remedial work from 1993 to 2001. This reduced the tilt to 3.97°. 

Fun Facts

  • Sometime around the 17th century Galileo Galilei took advantage of the unique geometry of this tower and conducted experiments on gravity by throwing objects down the leaning side of the Leaning Tower of Pisa. He used the tower to prove that ‘mass of falling objects has no influence on their speed’.
  • Surprisingly there are more leaning towers in the world. Venice, with its unstable soil, counts three leaning towers. Four other tilting towers can be found in Bologna, Caorle, Burano and Rome.

-Gur Rehmat Majithia 8A

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