Everybody knows that in the city of Pisa in Italy, there is a beautiful tower that ‘leans’. Very few people know the reason of its leaning. Every year thousands of people go there to see this wonder. It is made of white marble. The walls are four metres thick at its base. It has eight storeys and is 55.4 metres high and measures 15.8 metres round the bases. There is a stairway which leads to the top and has 300 steps. From its top one can have a magnificent view of the city and the sea which is ten kilometres away.
Now the question arises: what makes this tower lean and why does it not fall? Plumb line from the top is five metres away from the base, i.e. it leans over by five metres. If we drop a ball from its top, it would hit the ground five metres away from its base. It was intended as a bell-tower for the cathedral which is nearby. Its construction was started in 1174 A.D and completed in 1350 A.D. When the construction started nobody thought that it would lean, but it started leaning after the third storey was completed. The foundations of the tower were laid in sand and this may explain why it leans. Since the tower started leaning, the plans of its construction were modified and then the tower was completed. Since 1918, yearly measurements have been made. They show that the leaning is increasing. During the last one hundred years the tower has leaned another 30 cms.
But why does it not fall even while leaning? According to science, anything will remain stable as long as the vertical line drawn from its centre of gravity passes through its base. The centre of gravity is that point where the whole mass of the body is supposed to be concentrated. Till today the vertical line from the centre of gravity has been falling within the base of this tower. That is why it has not fallen. It is believed that when the tower leans further and the line from its centre of gravity pass out of its base, it will fall down. However, by using different new methods and techniques, Engineers and Technologists are now trying to arrest its further leaning.