Question

why is the speed of rotation decreases near the poles

Answer 1

As we move poleward, Earth's circumference decreases and therefore the speed of rotation decreases slightly since the equatorial belt of the Earth has to cover more distance than polar belt in same amount of time.

Answer 2

To measure the speed of rotation, there are two types of

speeds, linear and angular. The speed of rotation in general, of the Earth, can

should be measured by angular speed rather than linear speed.

The angular speed of Earth is that of 360 degrees, in 24

hours. This means that the angular speed at the equator, is the same, as it is

on the poles.

However, if we imagine that there is a pole which is

connecting the North and South poles, then that would be considered the axis,

on which the Earth rotates.

The Equator, is equidistant from both poles. The equator is

further away from the (just imagined central pole) than the North and South

poles. In this case, the same point on the equator has to travel a larger

distance, a larger radius or call it circumference, to get to the same point.

Therefore, the speed of rotation at the poles, decreases.

Formulas can be used to measure this, through velocity. Where

velocity is equal to distance divided by time and  Speed

= Distance / Time