How to read 57 ′ / D

How to read 57 ′ / D

57 points per day
It means to turn 57 minutes every day

Geography: what is the angular velocity of the earth's rotation? Linear velocity? Detailed!

There are two ways to describe the earth's rotation speed: angular velocity and linear velocity;
How to calculate the angular velocity? Every point on the earth rotates 360 degrees for a circle, and it takes nearly 24 hours, so how many degrees per hour is the angular velocity. If you calculate, you can divide 360 by 24 directly; the angular velocity of the two poles is equal, and the pole is 0;
Linear speed: it takes 24 hours for a point on the earth to rotate for a circle. Then the linear speed is equal to the circumference of the latitude circle of the store divided by 24. The linear speed decreases from the equator to the two poles, and the two poles are 0

1. The empty tape axis of the tape recorder rotates at a constant angular speed to rewind the tape. After rewinding, the final radius R1 of the tape reel is three times of the initial radius R2
The winding time is T1. If a thin tape with half the original thickness and the same length is rewound on the same tape axis, how long will it take T2?
2. When listening to the tape recorder, I found that after the time T1 = 20 minutes, the radius of the reel on the tape axis is reduced by half. How long does it take T2 to reduce the radius by half?
Why is the number of circles proportional to time in the first question and the length proportional to time in the second?
The first question is that angular velocity does not change, but the second question is that angular velocity does not change?

Considering with area method, the area of winding tape is the same at the same time