Finding the Circumference of the Earth



Our Earth – An Oblate Spheroid

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Contrary to common belief, the earth is not actually a perfect sphere. The earth is known an oblate spheroid. Oblate means that the earth is slightly wider or “stretched” at the equator or “middle” of the earth.

The reason the earth is oblate is because it is rotating or “spinning” on its axis. An axis is an imaginary line running from the North Pole to the South Pole.

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So why does the earth spinning make the earth stretched at the equator? Think about spinning a basketball. If you were to take a basketball and spin it, the middle “equator” would be spinning much faster than the top and bottom “poles”. If it spins fast enough, the ball begins to flatten slightly around the middle. Similarly, the rotating earth flattens slightly around the equator.

Finding the Circumference, Diameter, and Radius of the Earth

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Due to this stretching at the equator, the earth’s circumference is about 70 km (40 miles) wider at the equator than the poles. Circumference is the total distance around the earth.

If you wanted to dig a hole to the other side of the earth you would need to calculate the diameter. Diameter is the distance from one end of the earth to the other in a straight line. If you wanted to know the distance to the center of the earth you would need to calculate the radius. The radius is distance from one side of the earth to the center of the earth. The radius is half the distance of the diameter.

Using the figure ∏ “pie” or roughly 3.14 you can find the circumference, diameter, or radius of a sphere if one of the three is already known.

Use the following formulas to answer the questions below. The circumference of the earth at the equator is 40074 km. The circumference of the earth at the poles is 40007 km.

1. How far is it from one side of the earth to the other at the equator? Show all work. (C = ∏d)

__________ km

2. How far is it to the center of the earth from the North Pole? Show all work. (C = 2∏r)

__________ km

3. You are planning a trip from the Equator to the North Pole. Create a formula and then calculate how far you must travel. Show all work.

Bonus (5pts): If you were able to dig a hole from the North Pole to the South Pole and travel 100km/hr, how much faster would your trip be than traveling along the surface of the Earth at the same speed? Show all work.

Definitions

Directions: Write the definitions of the following terms.

Oblate Spheroid –

Equator –

Rotation –

Axis –

Circumference –

Diameter –

Radius -

Short Answer

Why isn’t the earth a perfect sphere? What region of the earth is wider than others and why? Using some of the vocabulary above, explain. (3 sentences minimum)

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