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### Earth's Rotational Speed

```
Date: 6/24/96 at 13:51:57
From: Anonymous
Subject: Label for Earth's Rotational Speed

Should the Earth's rotational speed be referred to in Revolutions
per... or as some refer to it, in mph? I am asking because it doesn't
seem to make a lot of sense to refer to it as a measurement of
settle this argument.

Thanks a lot -
Tony
```

```
Date: 6/24/96 at 14:24:2
From: Doctor Tom
Subject: Re: Label for Earth's Rotational Speed

It usually makes much more sense to speak in terms of revolutions
per hour or some such units, because the rotation speed in terms
of a velocity (mph or something similar) depends on the latitude.
At the poles, the velocity is zero; at the equator of the earth,
it's about 1000 miles per hour.  In Seattle (about 45 degrees up),
the speed is 1000*cos(45) miles per hour.

But it's perfectly correct to say the rotation speed at the
equator is X miles per hour, since you can work out other speeds
(or angular speeds) from this.

In physics, angular velocity is measured in terms of angle/time
(rotations per hour, or something like that).  That's because
the equations used to relate torque, angular momentum, moment
of inertia, and angular velocity must use those units.

-Doctor Tom,  The Math Forum
Check out our web site!  http://mathforum.org/dr.math/
```
Associated Topics:
High School Physics/Chemistry
Middle School Terms/Units of Measurement

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