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Earth Science Journal!
#6 Journal Entry: Shape of the Earth
Please write down three pieces of evidence for the shape of the earth.
We know that the Earth's shape is _______________ because...
1.
2.
3.
Please draw three ovals that represent the Earth's shape.
#1 wider along the equator,
#2 like an egg standing on end,
#3 is as perfectly round as you can (use a coin if you like).
Drawn to scaleChose which numbered "circle" would most closely resemble the shape of the Earth if it could be shrunk down to fit on your paper.
Write down your answer and give reasons for your choice.
Example: I think that #_____ best represents the shape of the Earth because...
The true shape of the Earth
Which is more round the earth or basketball?
Place your bets.I think that the Earth is (more, less, the same) roundness as a basketball.Put your guess down in your journal.
Let's take some measurements.
It is very easy to calculate the roundness of a spherical object. If you carefully take a string and measure the circumference around the spherical object going one direction (like around the equator), and compare the length of that string to one measured going around the object perpendicular to the first (around the Poles), dividing the two lengths gives you what is called the roundness factor.
Try it for yourself, just make sure you chose a string that does not stretch (dental floss works well).
If our basketball is perfectly round what would its roundness factor be?
_Any number_
Same number
A perfect sphere has a roundness factor of 1.
The closer to 1 the more perfectly round the sphere!
Basketball Data
Equatorial
Circumference72.8 cm
Polar
Circumference72.6 cm
Roundness Factor
72.8 cm ÷ 72.6 cm =
1.0028
Earth Data
Equatorial
Circumference40,076 km
Polar
Circumference40,008 km
Roundness Factor
40,076 km ÷ 40,008 km =
1.0017
Compare the roundness factors.
Which is more round?
Conclusion: The earth is more round (spherical) than a basketball!
How was your prediction?
I was correct the.....
I was incorrect the.....What did we find out?Understanding precise concepts and applying them to smaller objects "drawn to scale" can be very difficult. Small defects on small objects can turn out to be huge anomalies when blown up to the size of the Earth.
Those bumps on a basketball are many times larger than Mount Everest when blown up to the size of the Earth.
The depth of the ocean would compare to dunking a basketball in water and shaking only to be left with the film of water that remains. Our Atmosphere is just a thin blue line when seen from outer space.
A big blue marble is a good analogy for the smoothness and roundness of the Earth (to scale).
What did we find out?
The Earth is very round and smooth.
So should you have chosen #1, #2, or #3 at the beginning of this entry?
Drawn to scale, a perfect circle (#3) is the best model for the shape of the Earth.
Were you correct?
We have known that the Earth was round for some time in fact Eratosthenes calculated the Earth's circumference around the year 240 BC!
Please answer this question in your journal after watching the video above.
How did Eratosthenes know that the Earth had to be a sphere?
Evidence for a round Earth1. Best Evidence: Photographs and videos of the earth from space!
Seeing it is believing it!Watch the Earth LIVE from theNASA/DSCOVR satellite
Japanese weather satellite Live
2. Sinking ships: ships seem to sink because they are traveling over a curved surface.
3. Altitude of Polaris (North Star): if the earth were flat Polaris would always be at the same height (altitude). Polaris' height changes because we are traveling over a curved Earth.
Your latitude is equal to the altitude of Polaris!Using an astrolab
4. Stars' Path's are curved: if the earth were flat they would not have a curved arc as they appear to make circles in the night sky.
Photo above was taken by Michael Carlo.
Like photography?Learn how to take your own photo of Star Trails!
5. Lunar Eclipses: the Earth's shadow always appears curved when it falls on the surface of the moon.
Only a sphere "always" has a curved shadow.
6. Webcams from around the world show us the different time zones.Here is what Hollywood looks like when it is 9:00 AM in Wilson NY in September.
Why so dark?The Earth is round and the sun did not rise there yet!http://www.earthcam.com/usa/california/losangeles/hollywoodblvd/
http://www.earthcam.com/japan/tokyo/
We know that the shape of the Earth is very close to being a perfect sphere but with careful measurements, we have found that the actual shape is not quite perfectly round.
The Earth's shape is given a special name.
7. Do you know the scientific name for the Earth's shape?
Earth's shape = Oblate Spheroid
There is a 68-kilometer difference between the equatorial and polar circumference, and there must be a reason for the difference.
The question then becomes--Why?
8. Why isn't the Earth perfectly round?
If gravity pulls everything down to the center, how come the Earth slightly bulges along the equator and is only slightly flattened at the poles?
Shouldn't it be perfect?
What is throwing it off?
Cup half full, sphere, bubble spinner?
Question #9
We weigh more at the poles because we are closer to the more dense earth's core.
10. Explain how the Earth's shape, the force of gravity on the Earth's surface, and rotation of the Earth are related.
1. Rotation of the Earth forces the equator to bulge a bit.
2. This makes the equator further from the core of the Earth.
3. Gravity decreases slightly at the equator because it is further from the dense core of the Earth.
Evidence of Earth's Rotation!
Draw a circle like the one above.
11. Predict where the pendulum will end up swinging by the end of class.
Explain your prediction.
If we start the pendulum swinging in one direction and nobody touches it, shouldn't it keep going in the same direction?
Which way does the earth spin?
Which one is correct?The earth is often shown spinning the wrong way even on educational programs.Evidence of the Earth's rotation!12. Why does the sunrise and set?Because the Earth spins under the sun!
Next time you are watching the sunshine, re-frame yourself, and feel the spin.
Sunrises in the East
Because we are spinning toward the sun.
Sunsets in the WestBecause we are spinning away from the sun.13. Based on these observations, what direction does the Earth spin?Earth Spins from West to East!When you see the sunrise or set, I want you to imagine what is really happening.Time Lapse Sky Shows Earth Rotating Instead of Stars.
How fast does the Earth spin?One day = one rotation (one spin)14. How long is a day?24 hours15. How many degrees is one spin?360 degrees16. How many degrees per hour does the Earth Spin?360°/24hours = 15 degrees/hour17. Draw this circle representing the Earth.
Label the direction and speed of rotation.*Like a Merry-go-round "WeeeeeeeeeE" spin from West to East!The sun rises in the East because we are spinning toward it.
18. Does the Earth spin clockwise or counterclockwise?
Why is that a badly stated question?From the North Pole = counter-clockwiseFrom the South Pole = clockwiseBe careful when you describe the direction of the Earth's rotation.If you say counterclockwise or clockwise your answer is always wrongunless you state which pole you are looking at.Experimental Evidence that the Earth rotatesWouldn't it seem magical if you started a pendulum swinging in one directionand it changed direction by itself?Well, that's what Jean Foucault found to happen.
Foucault pendulum
Watch the Earth Turn!
JOURNAL REFLECTION – In complete sentences, explain what you learned about the shape of the Earth, the direction of rotation, and how the Earth's rotation affects the Earth's shape. Explain why Foucault's pendulum “appeared” to change directions during the course of our class.
Bonus Activities
Where does the Gnome weigh more, and why?
Bonus:
Print out the following articles and answer the questions.
Google doodle honors Foucault and his pendulumhttp://www.latimes.com/science/sciencenow/la-sci-sn-google-doodle-foucault-20130918,0,7291758.story
It may be hard to fathom, but the idea of Earth rotating on its axis, first proposed in the 6th century, took many centuries to gain favor and many more to be demonstrated. When Foucault was born, science accepted the Copernican theory of celestial motions well accepted. It elegantly explained the apparent "rise" and "set" of the sun, but it was difficult to "prove" by experiment.
Some folks tried to drop stones down a mineshaft to see if they deviated. Others tried something similar to the trajectory of cannonballs. But the mine shaft was too short, compared with Earth's radius, and the time traveled by the cannonballs likewise was too short to measure any difference.
The son of a publisher, Foucault showed an early aptitude for all things mechanical and a growing aversion to all things bloody. So he gave up a medical curriculum and opted for physics.
He built his first pendulum with six feet of wire, an 11-pound ball, and a candle that "launched" the ball by burning through a string to which the ball was attached (to prevent any directional effect of pushing the bob).
His pendulum became a sensation, and he constructed several for public displays, the most famous of them at the Pantheon in Paris.
The California Academy of Sciences museum in San Francisco has a massive Foucault pendulum that swings through an arc of about 220 degrees daily.
Why not 360 degrees, you ask? The pendulum's motion is dependent on the latitude of Earth. Foucault's likewise moved 270 degrees in 24 hours. A pendulum at the North Pole would spin the full 360 degrees.
You're probably already wondering why the pendulum doesn't just slow down and stop, eventually. It does. In the early Foucault experiments, this didn't matter so much, because it swung long enough to see the floor shift in relation to the arc of the pendulum. But as the pendulum became more of a sensation, people invented ways to overcome the resistance that slows the bob.
Designers these days use electromagnets near the fastening point for the cable to overcome that force and keep things swinging. At the academy, this electromagnet turns on and off when the cable passes a beam of light.
Explain how the Foucault pendulum works.
Does your weight change between the poles and the equator?
http://curious.astro.cornell.edu/question.php?number=310Hi. I'm a seventh-grade student in Washington. I had this question: The earth is spinning, so there is more centrifugal force towards the equator of the earth than the north pole, because the middle of the earth is spinning faster. So if you lived on the equator wouldn't you weigh less than someone who lived on the north pole, because there is more force trying to pull you away from the earth? Thanks for your time and effort. I really appreciate it.
You are right that because of centripetal acceleration, you will weigh a tiny amount less at the equator than at the poles. Try not to think of centripetal acceleration as a force though; what's really going on is that objects which are in motion like to go in a straight line and so it takes some force to make them go round in a circle. So some of the force of gravity is being used to make you go round in a circle at the equator (instead of flying off into space), while at the pole, this is not needed. The centripetal acceleration at the equator is given by 4 times pi squared times the radius of the Earth divided by the period of rotation squared (4*pi2*r/T2). The period of rotation is 24 hours (or 86400 seconds) and the radius of the Earth is about 6400 km. This means that the centripetal acceleration at the equator is about 0.03 m/s2 (meters per second squared). Compare this to the acceleration due to gravity which is about 10 m/s2 and you can see how tiny an effect this is - you would weigh about 0.3% less at the equator than at the poles!
There is an additional effect due to the oblateness of the Earth. The Earth is not exactly spherical but rather is a little bit like a "squashed" sphere, with the radius at the equator slightly larger than the radius at the poles (this shape can be explained by the effect of centripetal acceleration on the material that makes up the Earth, exactly as described above). This has the effect of slightly increasing your weight at the poles (since you are close to the center of the Earth and the gravitational force depends on distance) and slightly decreasing it at the equator.
Taking into account both of the above effects, the gravitational acceleration is 9.78 m/s2 at the equator and 9.83 m/s2 at the poles, so you weigh about 0.5% more at the poles than at the equator.
Why do we weigh more at the poles?
What has more of an effect on your weight, the spin or the bulge?
