**Three Gorges Dam Changed The Earth's Rotation**

Three Gorges Dam, the worlds largest hydroelectric power-plant facility situated on the Yangtze river of China in Hubei province is considered to be a remarkable monument of civil engineering structure. In universities, students of Civil and Environmental Engineering (CEE) are often assigned to submit reports based on this monument due to its remarkable outcomes and the many impacts it posed over the human community as well as the environment. Massive relocation program, destruction of archaeological sites and environmental sustainability are the major impacts often considered. But there was a bit controversial topic aired in 2010 among the scientific community when NASA proclaimed that the structure might have posed an impact over earth's rotation. For a short period of time, we the students had this question among ourselves, how it did? Well, here we have tried to explain the fact in a very easy way.

We have tried to conduct a theoretical experiment and here is it:

Considering figure – 1 (at bottom)

m1 = 1 unit and m2 = 2 unit; are two particles of one single object.

r1 = 1 unit; is the distance between the rotational axis and particle m1

and r2 = 2 unit; is the distance between the rotational axis and particle m2.

P1 and P2 are two positions.

The particles take 1 unit of time to rotate 90 degree to reach P2 from P1 [

So, the angular velocity,

ω = dϴ / dt = 90 degree per unit

As we know, moment of inertia, I = ∑ mr^2

So, I = m1r1^2 + m2r2^2 = 1 + 2 x 4 = 9 unit

So, Kinetic Energy needed to complete the rotation = Iω^2 = 9 x (90)^2 = 72900 unit

Now, considering figure – 2,

m = m1 + m2 = 3 unit

r2 = 2 unit

So, I = 3 x 4 = 12 unit

K.E = Iω^2 = 12 x (90)^2 = 97200 unit.

So, the required amount of kinetic energy is increased with respect to the change in distance of the particle from the rotational axis. Now, consider the equilibrium state (environmental sustainable situation) of earth. So, for a moment we think, the energy is fixed and it is 72900 unit. Means, we cannot provide more than 72900 unit of energy to complete the rotation.

So, K.E = 72900 unit (fixed)

I = 12 unit (fixed)

So, ω^2 = 72900 / 12

So, ω = 77.943 unit

So, we can clearly see that the angular velocity has been decreased from 90 to 78 unit to keep the energy consumption stable. That’s exactly how the Three Gorges Dam affected earth’s rotation.

The Dam was made out of concrete which is a composite material of sand, gravel and cement. These component materials were scattered around the earth's surface until it was collected and processed to make concrete. So, basically all the individual masses altogether resulted in a increase in mass in a particular position i.e the location of the dam and thus posed further effects.

But the good news is, it only increased the day length by 0.06 microseconds which is very small. So, the effect is very insignificant in amount. But it is also true about one fact that our decisions can be very destructive for the sustainability of our environment.

We have tried to conduct a theoretical experiment and here is it:

Considering figure – 1 (at bottom)

m1 = 1 unit and m2 = 2 unit; are two particles of one single object.

r1 = 1 unit; is the distance between the rotational axis and particle m1

and r2 = 2 unit; is the distance between the rotational axis and particle m2.

P1 and P2 are two positions.

The particles take 1 unit of time to rotate 90 degree to reach P2 from P1 [

*although the angular velocity is often expressed as radian/sec, to keep it simple we used degree and the word ‘unit’*].So, the angular velocity,

ω = dϴ / dt = 90 degree per unit

As we know, moment of inertia, I = ∑ mr^2

So, I = m1r1^2 + m2r2^2 = 1 + 2 x 4 = 9 unit

So, Kinetic Energy needed to complete the rotation = Iω^2 = 9 x (90)^2 = 72900 unit

Now, considering figure – 2,

m = m1 + m2 = 3 unit

r2 = 2 unit

So, I = 3 x 4 = 12 unit

K.E = Iω^2 = 12 x (90)^2 = 97200 unit.

So, the required amount of kinetic energy is increased with respect to the change in distance of the particle from the rotational axis. Now, consider the equilibrium state (environmental sustainable situation) of earth. So, for a moment we think, the energy is fixed and it is 72900 unit. Means, we cannot provide more than 72900 unit of energy to complete the rotation.

So, K.E = 72900 unit (fixed)

I = 12 unit (fixed)

So, ω^2 = 72900 / 12

So, ω = 77.943 unit

So, we can clearly see that the angular velocity has been decreased from 90 to 78 unit to keep the energy consumption stable. That’s exactly how the Three Gorges Dam affected earth’s rotation.

The Dam was made out of concrete which is a composite material of sand, gravel and cement. These component materials were scattered around the earth's surface until it was collected and processed to make concrete. So, basically all the individual masses altogether resulted in a increase in mass in a particular position i.e the location of the dam and thus posed further effects.

But the good news is, it only increased the day length by 0.06 microseconds which is very small. So, the effect is very insignificant in amount. But it is also true about one fact that our decisions can be very destructive for the sustainability of our environment.