# Thread: circumference of the Earth

1. ## circumference of the Earth

Can anyone tell me how to set up the equation to find out how far it is around the Earth at the Equator? Tomorow I have to mail off a PHS 111 lab that is due, so any immediate help anyone could offer would be greatly appreciated. THANKS!!!!!!!!

2. Originally Posted by Susan Campbell
Can anyone tell me how to set up the equation to find out how far it is around the Earth at the Equator? Tomorow I have to mail off a PHS 111 lab that is due, so any immediate help anyone could offer would be greatly appreciated. THANKS!!!!!!!!
we would need to know the radius of the earth. was that given to you?

when you find the radius use the following formula for the circumference:

$\mbox { Circumference } = 2 \pi r$, where $r$ is the radius

So, $\mbox { Circumference } = 2 (6378.1) \pi = 12756.2 \pi \approx 40074.78 \mbox { km}$

3. Originally Posted by Susan Campbell
Can anyone tell me how to set up the equation to find out how far it is around the Earth at the Equator? Tomorow I have to mail off a PHS 111 lab that is due, so any immediate help anyone could offer would be greatly appreciated. THANKS!!!!!!!!
Hello,

you can use another method:

If you know the distance between 2 points on a circle of longitude or the equator then you can calculate the circumference by:

d : difference of degrees
D: distance between the 2 points in km

then

$c = \frac{360^\circ}{d} \cdot D$

Example:
First point on the equator at 10°W
Second Point on the equator at 16° W
Distance 667.9 km

$c = \frac{360^\circ}{6^\circ} \cdot 667.9\ km = 40074 \ km$