# How China Slowed The Rotation Of The Earth

Shobhit Tripathi
Mar 18, 2019   •  87 views

Have you ever thought that building a dam would decrease the rotation of the earth and can even increase the length of our day by 0.06 microsecond? How building a dam would shift the pole position by 2 centimeters (0.8 inches)?

China has constructed Three Georges Dam in the year 2008. The Georges Dam was built across Yangtze river in Yiling District, Yichang Hubei. This hydroelectric gravity dam is the world’s largest power station in terms of installed capacity (22,500 MW). When the water level is maximum at 175 meters (574 ft) over sea level (91 meters (299 ft) above river level), the reservoir created by the dam is about 660 kilometers (410 mi) in length and 1.12 kilometers (0.70 mi) in width on average. The total surface area of the reservoir is 1045 square kilometers, and it will will flood a total area of 632 square kilometers, of land. The reservoir will contain about 39.3 cu km (9.43 cubic miles) of water. The Dam was constructed and was fully operational on July 4, 2012. In the year 2014, it has created the world record by producing the total energy of 98.8 Terawatt hours (TWh). It contributes 10% of energy to China’s population.

Apart from electricity, the Dam is supposed to increase the Yangtze river shipping capacity and reduce the potential for flood downstream by providing flood storage space. China regards this project as a huge success. It is also supposed that this dam will reduce greenhouse emission gases.

Imagine yourself standing your arms tightly closed to your body and start spinning your body. Now in second case, imagine yourself standing to extend your arms and start rotating. You will see the difference. When your arms were closed to your body, you were spinning faster as compared to when you were extending your hand. This is because of the phenomenon called Moment of inertia. Moment of inertia actually decides how difficult it is to change its angular motion about that axis.

Raising 39 trillion kilograms of water 175 meters above the sea level will obviously increase the moment of inertia of earth and slow down its rotation. NASA scientist calculated the shift of such mass would increase the length of the day by 0.06 microsecond and has slightly tilted the position of the pole by 2 centimeters. It is impossible to observe these changes since the shift is too small. Along with this impact on the earth, the dam has displaced 1.3 million people and have a severe impact on the surrounding.The dam has also increased the risk of landslide.

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