How Fast Does The Earth Spin?
To work out how fast the Earth spins, you first need to determine the time it takes to fully complete a single rotation. A full single rotation is what we call a day, and it takes roughly 23 hours, 56 minutes and a few seconds to complete. Our clocks are set for a 24 hour day because it is easier to round up in equal segments. The difference in time between a ‘true’ day, and a ‘24 hour day’, equates to around a quarter of a day per year, and is the reason we have a leap year every 4 years.
Once we have determined the ‘time’ of a single rotation, we can work out the ‘speed’ with a few more numbers. We need to work out the circumference of the Earth, and divide this number by the ‘time’ of rotation. The circumference of the Earth can be worked out with the following formulae:
C (circumference) = 2 x Pi x r (radius).
We know that the radius at the equator is approximately 6374 km, or 3,981 miles – slightly shorter at the poles, but we will use the equatorial radius for this example.
So how fast does the Earth spin?
C = 2 x 3.14 x 6374
C = 40030.2 km, or 25,020 miles.
The Earth spins, therefore at Circumference / Rotation Time (1 Day)
40030.2 km / 23.56 hours = 1699 km per hour
25,020 miles / 23.56 hours = 1062 miles per hour
If, we knew the circumference and not the radius of the Earth, you could adjust the formula accordingly to:
Radius = Circumference / Pi / 2
We know the equatorial radius to be true to 40,030.2 km as confirmed by Nasa (https://solarsystem.nasa.gov/solar-system/sun/by-the-numbers/)
Why do we not feel the Earth spinning?
Well, the speed of rotation and the force of gravity are the reason for this. Because the speed of rotation is constant, we feel stillness. Without an acceleration or slowing down there is no reference point to feel a change in motion.
Think about a plane taking off. On the runway, when the thrust kicks in and the plane accelerates you are pushed back into the seat with a great sense of changing speed. But when the plane is coasting in the sky at a steady speed, there is no sensation of movement.
If the Earth was to speed up or slow down at a considerable rate we would feel that sense of motion, but because it is steady, we do not.
- The Earth Spins at roughly 1062 miles/ 1699 km per hour