Name _________________ Period _______ Partners________________
The Earth’s Shape
Lab # ____
Introduction: Pictures of the earth taken from space show that the earth appears to be perfectly
round and smooth. However, to us, the earth appears to have a highly irregular surface. In addition,
accurate measurements of the earth’s shape show that the equatorial diameter is slightly different
than the polar diameter.
Objective: To understand the true roundness and smoothness of the earth
Vocabulary:
Relief
Model
Oblate spheroid
Sphere
Procedures:
A. Roundness
The ratio of the polar diameter to the equatorial diameter of a sphere is a measure of its
roundness. We call this a roundness ratio.
1. Use the values given for the equatorial and polar diameters of the earth in the data
chart on the report sheet to calculate the roundness-ratio of the earth. Record this
value on the chart provided.
2. Measure the equatorial and polar diameters of the diagram in your lab. Record these
measurements on the chart provided.
3. Calculate the roundness-ratio for the diagram using the data from Procedure 2.
Record this value on the chart provided.
Report Sheet
A. Roundness
POLAR DIAMETER
Earth
12,714 km
Globe
Diagram
cm
EQUATORIAL DIAMETER
ROUNDNESS RATIO
12,756 km
cm
B. Smoothness
A relief globe shows the relative height of its surface features such as mountains. It is a
scale model of the earth. The following procedures will show you if these features are
constructed to scale on the enclosed diagram. To do this you must use the following
proportion:
Actual height of the surface feature (in km) = To Scale Height of Everest (cm) (Solve for this)_
Earth diameter (in km)
Relief globe diameter (in cm)
When you substitute values into the equation, you will have one unknown. The “To
Scale Height of Everest.” Use the actual height of Mt. Everest divided by the diameter
of the earth which is given. Measure the diameter of the globe using your cm ruler.
Note: The following chart information is to be recorded on the data chart under ‘smoothness’ on your
report sheet.
1. Measure the diameter of the Earth in cm using the diagram of the earth.
2. The actual height of Mt. Everest, the highest point in the world, is 8.8 km.
3. The average diameter of the earth is the average of the polar diameter (12,714) and the
equatorial diameter (12,756 km). This value is 12735 km
4. Measure the equatorial diameter of the diagram globe in cm to the tenths place.
5. Using the values obtained in procedures 2 through 4 and the above equation, solve for the
relief globe height of the surface feature (Mt. Everest) to correct scale for the globe.
6. Determine the percentage error between the height of Mt. Everest on the diagram and the
height it should have been if drawn to the correct scale.
a. Smoothness
Height of Mt. Everest on the diagram (measure)
___________________cm
Actual height of Mr. Everest
8.8 km
Average diameter of the earth
12,734 km
Average diameter of diagram (measure)
___________________cm
Correct scale height of Mt. Everest on globe diagram ___________________cm
Percent Error (comparing the correct scale height to measured height of Mt. Everest)
_________%
Show all work for the calculations above.
Actual height of the surface feature (in km) = To Scale Height of Everest (cm) (Solve for this)_
Earth diameter (in km)
Relief globe diameter (in cm)
8.8 km =
12,734 km
To Scale Height of Everest (cm) (Solve for this)_
Relief globe diameter (in cm)
(8.8 x Diagram globe diameter (cm) = To Scale Height of Everest (cm)
12,734
The diagram below represents an average classroom globe.
Mount Everest
Discussion questions: (ANSWER IN COMPLETE SENTENCES!!!!)
1. Using the roundness ratio you calculated, which is a more perfect sphere? The globe diagram
or the earth?
2. How does the earth’s polar diameter compare with its equatorial diameter?
3. Is the earth a perfect sphere? How does your data confirm your answer?
4. CHALLENGE: A 0.1cm deep scratch was made in the surface of a globe with a diameter of 40
cm. Calculate the actual depth of the surface feature (represented by the scratch) on the real
earth. Use the information you gained from the previous calculations. (SHOW ALL WORK!!!)
5. In terms of roundness and smoothness, name an object which would be a good model of the
earth. Explain your choice.
Conclusion question :
Describe how this lab helped you to understand that the earth is both round and smooth. Include
specific information. Answer in complete sentences.