Can a Hydroelectric Dam Actually Make the Days Longer?

What number of occasions have you ever mentioned, “I want the times had been longer”? Nicely, NASA scientists say the development of China’s Three Gorges Dam really did make the times longer, by slowing the rotation of the Earth. Hallelujah! Additional time you should use to study a brand new language, catch up at work, and even higher, sleep in.

This raises loads of questions. To begin with, is it true? Did the dam really make our days longer? And if that’s the case, why? And simply how a lot additional time are we speaking about right here? I imply, it is advisable plan your schedule, proper? Ought to we construct extra big dams to get much more time?

Angular Velocity

To reply these questions, we’d like three fundamental physics concepts: (1) angular velocity, (2) angular momentum, and (3) the second of inertia. I’ll clarify every of those.

First, right here’s slightly experiment that you are able to do your self. If in case you have a rotating desk chair, get it spinning together with your ft off the bottom and your arms tucked in. Now, earlier than you throw up, prolong your arms. It slows you down, proper? This is a model with a human on a rotating platform:

The velocity of rotation is what we name angular velocity, represented by the Greek letter omega (ω). Why “angular”? Right here’s a two-dimensional instance under. Consider this circle as centered on an xy coordinate aircraft. I’ve drawn a radius (R) to some extent on the circle the place it cuts the horizontal axis: