Notes: Key Characteristics of
Earth’s Motion
• Objectives:
– Differentiate between rotation and revolution.
– Identify and explain the evidence of earth’s
motions.
– Relate Earth’s motions to time and distance
as a part of the universe.
The Rotating Earth
• Rotation: the spin of a body on its axis
– 24 hours = 1 rotation
– From west to east. Sun rises in east first.
The Rotating Earth
• Tools and Evidence:
– The Foucault Pendulum: A weight attached
to a wire which is attached to the ceiling.
• Hangs free from contact with the floor. (Earth’s
surface)
• The weight moves back and forth in the same line
unless something physically changes its path.
• The floor (Earth’s surface) is what moves, making
the weight seem to change direction.
• This proves Earth rotates.
The Rotating Earth
• Tools and Evidence:
– View the following links for examples of the
Foucault Pendulum.
• http://www.schoolforchampions.com/science/pendulum.
htm
– Scroll down to see a real large-scale example in Paris, France.
Read the surrounding information.
• http://www.animations.physics.unsw.edu.au/jw/foucault
_pendulum.html
– Scroll down the picture of Foucault himself to analyze the
small-scale example by the University of New South Wales.
Read the surrounding information.
The Rotating Earth
• Tools and Evidence:
– The Coriolis Effect: Earth’s rotation causes
free moving objects touching Earth’s surface
to appear to curve. (not follow a straight path)
• Ocean currents, winds, storms, etc.
– See the following links for examples.
• http://www.baesi.org/TRG/coriolis/CORIOLIS.MOV
• http://www.classzone.com/books/earth_science/ter
c/content/visualizations/es1904/es1904page01.cfm
The Revolving Earth
• Revolution: The motion of a body that
travels around another body in space; one
complete trip along an orbit.
– 365.25 days for Earth around Sun.
– Just think about this idea: Earth’s speed in orbit.
•
•
•
•
Earth’s orbit is approx. 584,000,000 miles.
Divide by 365 = 1,600,000 miles in a day.
Divide by 24 hours = Approx. 67,000mph avg. speed.
1,116 miles per minute or 18.6 miles per second.
The Revolving Earth
• Earth’s orbit is an ellipse: Closed curved, but
not a perfect circle. Pg. 668, figure 2
The Revolving Earth
• Evidence: When the earth is at different locations
in its orbit around the sun…
– We face different directions in the universe.
– We see different stars in the night sky.
The Revolving Earth
• Distance from the Sun does not affect the seasons.
– We are actually closer in January than in July!
– 2.5 million km difference = 1.5% of total distance from
Sun. Insignificant to determine temperature changes.
Question
• What does affect the seasons?