## Earth's Rotation

How fast is the Earth spinning?

1 – What do we need to know?  We need to know the Circumference of the Earth at its widest part, the Equator.  We also need to know the time that it takes to make one complete revolution.  Speed is stated as a distance over time.  Like “miles per hour” or “feet per second”.

2 – To calculate the Circumference of the Earth we will use the formula

for the Circumference of a circle. C = piD     We know that pi = 3.14, so let’s find out what Diameter is.  Easily found on Google.

The Diameter of the Earth is 7,829 miles.

Circumference = piD = 3.14 x 7,829 miles = 24,583 miles.

It takes the Earth 24 hours to make 1 rotation.  Since we usually think of speed (or velocity) in terms of “miles per hour” or “kilometers per hour”, we will divide the Circumference by 24 hours / revolution.  24,583 miles / 24 hours = 1,024 miles per hour.

To summarize our calculations:  If you are standing still at the Earth’s equator, you are moving at 1,024 miles per hour.