![]() How many songs can you name that talk about slowing down time?.What is the highest angular velocity a human can have without falling apart?.What if everyone got in their car and drove East at about 70 mph? How would this effect the length of the day?.What if all the people on Earth moved as far North as possible and then they all spun? How much longer would a day be?.How fast would a person have to spin in order to increase the day by 1 second? Ignore relativistic effects at first just to see what kind of answer you get.We can't slow down a day, but we can enrich our lives with physics homework. Since there isn't any torque, the angular momentum of the Earth before the spin is equal to the new angular momentum of the Earth plus the angular momentum of the person. Now I can write the angular momentum of the Earth plus person as (just the z-component): If I call Earth's rotation axis the z-axis then I can write: If the person is in New Orleans, the latitude is about 30 degrees. Only the component of the spinning person's angular momentum in the same direction as the Earth's angular momentum maters. Technically, it will do something - it will change the axis of rotation since the Earth is a zero-torque system - but I'm just considering the length of the day so I will ignore that. Where on the Earth is this spinning person? If they are on the equator (and standing up straight), the spin will have no effect on the length of the day. Now, how fast can this person spin? According to this video, an ice skater can spin up to 400 rpm (41.9 radians/second). I can calculate the moment of inertia for a spinning solid sphere as:īut what about the spinning person? Let's say that the person is a cylinder - why not? How about this person-cylinder has a mass of 70 kg and a radius of 0.15 meters (which is probably too high, but it's just an estimate). I guess I can also ignore the angular momentum of the Earth as it moves around the Sun. Oh, the angular speed of the Earth is about (1/24) revolutions per hour. Second, I will pretend that the Earth is on a fixed and non-wobbling axis (which it isn't). ![]() I am going to approximate the Earth as a solid and uniform density sphere (which it isn't - see this example).
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