how often Have you said, “I wish the days were longer”? Well, NASA scientists say that the construction of China’s Three Gorges Dam has actually made the days longer by slowing the Earth’s rotation. Hallelujah! You can use the extra time to learn a new language, catch up on work, or, even better, sleep.
This raises many questions. First of all, is it true? Did dams really make our days longer? And if so, why? And how much extra time are we talking about here? I mean, you have to plan your schedule, right? Should we build bigger dams to gain more time?
angular velocity
To answer these questions, we need three basic physics ideas: (1) angular velocity, (2) angular momentum, and (3) moment of inertia. I will explain each of these.
First, here’s a little experiment you can do yourself. If you have a swivel desk chair, rotate it while keeping your feet off the ground and your arms inward. Now, before throwing up, extend your arms. It slows you down, doesn’t it? Here’s a version with a human on a rotating platform:
Video: Rat Allen
the speed of rotation which we call angular velocityRepresented by the Greek letter omega (ωWhy “Angular”? Here’s a two-dimensional example below. Consider this circle centered at one xy coordinate plane. I have drawn a radius (R) at a point on the circle where it intersects the horizontal axis: