The Nobel-prize-winning physicist, Enrico Fermi, came up with this simple and intuitive way to deduce the circumference of the earth.
1. How many time zones do you pass through when you fly from New York to Los Angeles?
Answer, 3
2. How many miles is it, about, over that same distance?
Answer, about 3000.
3. How many miles per time zone, on average?
Answer, about 1000
4. How many time zones must there be around the world?
Answer, 24 because there are 24 hours in a day
5. How many miles around the world?
Answer, 24 time zones x 1000 miles per time zone = 24000 miles
Yes, it is about 24000 miles around the world.


So how do I get the diameter of the Earth

1. the formula for a circle is 2 pi r, right? where r is the radius and pi is about 3

2. so 24000 mi = 2 x 3 x r = 6 x r

3. therefore 24000 mi / 6 = r = 4000 mi

4. the diameter of the earth is 2 x r = 8000 mi, where the diameter is 2 times the radius

5. 1 mi = 1.6 km so 8000 mi x 1.6 km/mi = 12800 km

(the correct answer is ~12742 km)


So you can always figure out the dimensions from your basic knowledge of traveling!

Go back to Lecture 6