Download How the Rotation of Earth Affects Our Life

Earth’s Motions
Earth’s Motions – Big Questions:
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How can we make a model to help us understand our
universe?
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What are the motions of the Earth?
How do we know?
How do the motions of the Earth affect our observations?
Yes, the Earth really is a SPHERE!
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http://testtube.com/dnews/how-we-know-the-earth-isn-tflat/
Earth’s Motions
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There are three major motions of Earth
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Rotation
Revolution
Precession
ROTATION
Rotation
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Earth turning or spinning on an axis
How does the sun appear to
move in our sky? WHY?
Because the Earth turns on its axis from
the West to the East (counter-clockwise)!
Effects of Earth’s Rotation…
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We experience day
as our location on
Earth turns to the
sun and night as it
turns away from the
sun
When we look
south, the sun, stars,
moon, planets, and
& constellations all
appear to rise in the
East and set in the
West
Why do the star trails in the
southern sky look different
than the ones in the
northern sky??
Because the Earth’s axis is tilted toward
Polaris, so stars in the north appear to circle
around that axis of rotation.
Effects of Earth’s Rotation: Coriolis effect
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Because the Earth is wider at the equator, Earth rotates faster
at the equator than it does at the poles
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In the Northern Hemisphere winds, weather patterns, water
currents, airplanes, etc. all appear to deflect to the right
because the Earth is moving underneath them.
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https://www.youtube.com/watch?v=mPsLanVS1Q8
Effects of Earth’s rotation…
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Plane flights
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Space flights
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pilots and navigators
must compensate for
objects veering to the
right
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Creates special issues for
astronauts in space
because they move at a
different rate than Earth
Because of Earth’s Rotation
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Winds
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Distribution of Rain
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Uneven heating of the
atmosphere causes winds
blow from areas of high
pressure to areas of low
pressure
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If not for the deflection
caused by the rotating
Earth, the equator would
get constant rain and north
& south would be deserts.
Evidence the Earth Rotates:
The Foucault Pendulum
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A ball swinging back and
forth on a string is called
a pendulum.
In 1851, French scientist
Léon Foucault observed
that his pendulum
seemed to change
direction over time.
What force was causing
this change in direction?
http://www.youtube.com/watch?v=C3-uFao4dxQ
The Foucault Pendulum
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Forces acting on a pendulum:
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Inertia causes it to swing straight out (Newton’s First Law of Motion)
Gravity pulls it back down (Newton’s Law of Gravity)
Air resistance makes it swing in shorter arcs over time
(friction is a force that acts against inertia)
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So what makes the pendulum change directions?
Pendulum as Evidence that Earth rotates:
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There is no force acting on the pendulum to make its plane of
oscillation rotate
The pendulum seems to change its path during the day, but
actually it is the floor beneath it that changes, being twisted
around by the daily rotation of earth.
At the north pole the apparent rotation
would be a full circle of 360 degrees
each day, or about 15 degrees per hour
Evidence of Earth’s rotation
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Astronauts have actually observed Earth’s rotation from
space!
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https://www.youtube.com/watch?v=eqCyHeJzO4s
All Planets Rotate:
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Rotation times:
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Mercury…………………58 Earth days
Venus………………….. 243 Earth days
Earth……………………23 hours 56 minutes
Mars…………………….24 hours 37 minutes
Jupiter…………………..9 hours 50 minutes
Saturn…………………..10 hours 14 minutes
Uranus………………….18 hours
Neptune…………………18 hours 10 minutes
Very similar
Which two planets have the longest periods of rotation?
Which planet has the shortest?
Which planet’s period of rotation is almost the same as Earth’s?
REVOLUTION
Revolution
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Earth revolves around the Sun at an average speed of
about 27 km/s or about 66,000 mph!
One trip around the sun on Earth’s elliptical orbit equals
one year.
Earth’s Revolution in action…
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http://www.classzone.com/books/earth_science/terc/cont
ent/visualizations/es0408/es0408page01.cfm?chapter_no=
04
Earth’s Orbit
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We are closest to the Sun at perihelion on January 3rd
(147 million kilometers)
We’re a little further from the Sun at aphelion on July 4th
(152 million kilometers)
Observational Evidence of Earth’s
Revolution: Changing Constellations
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As earth moves along its orbit, we face the sun from
a different perspective and we view different areas of
space at night.
Most of the constellations we can see in the summer
are not visible in the night sky during the winter.
This is evidence that Earth has changed locations in
space!
All planets revolve around the sun
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All Planets revolve around the sun near the same ecliptic plane
as Earth.
Remember Kepler’s third law… outer planets have longer
orbital periods than inner planets do.
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Mercury………………...……….88 days
Venus……………………………225 days
Earth…………………………….365.25 days
Mars…………………………….687 days
Jupiter…………………………..12 years
Saturn…………………………..29.5 years
Uranus………………………….84 years
Neptune………………………..165 years
Understanding Orbital Motion
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The universal law of gravity allows us to understand
orbital motion of planets and moons:
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Earth and moon attract each other through gravitation.
Since Earth is much more massive than the moon, the
moon’s effect on Earth is small.
The moon’s inertia would cause it to move in
a straight line (V), but…
v
Earth’s gravitational force constantly
Moon
accelerates the moon towards Earth (F)
Gravity is constantly changing
the moon’s direction of motion (Dv) ,
holding it on its almost circular orbit.
Dv
v’
F
Earth
Video : gravity and orbits
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http://svtube.svsd.net/play?id=uzptg84xwc
Precession
Precession
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Earth’s “wobble” on its
axis
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Takes ~26,000 years to
complete one wobble
What causes Precession?
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The Earth is slightly oblate
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it bulges in the middle
~0.34% larger at equator due to its rotation and the fact that it
is not completely rigid.
The Sun and Moon have non-uniform gravitational forces
on the Earth, pulling harder on the near side of the bulge
than on the far side. (gravity weakens with distance)
Consequences of Precession
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Polaris marks the north
pole today
Thuban was the pole
star in 3000 BC
Vega was in 12000 BC
Polaris will become the
north star again around
27800 AD
Earth’s motions and TIME
A year, a day, a month…
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A year is linked to Earth’s revolution (one orbit)
A day is linked to Earth’s rotation (one spin)
A month is linked to the cycle of the moon
BUT… each of these things can be defined in different
ways. How do you know when it’s been one full rotation?
One full orbit? One full moon cycle?
For example: Sidereal Day vs. Solar Day
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sidereal (or star) day:
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It takes the earth 23 hours and 56 minutes to rotate once with
respect to the stars. This is one sidereal (or star) day.
solar day:
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During that time, the earth has moved a bit along its orbit
around the Sun. So…
It takes about 4 minutes longer for the Sun to return to the
same position in the sky
Because we use the solar day, the stars rise and set 4 minutes
earlier each day.
Orbital Motion in One Solar Day
Earth’s Motions – Big Questions:

How can we make a model to help us understand our
universe?
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
What are the motions of the Earth?
How do we know?
How do the motions of the Earth affect our observations?