1. Earth Notes
Chapter 12

2. Rotation vs. Revolution
Rotation- spinning of earth on its own axis:
24 hours = 1 day = 1 rotation
The Earth’s rotation causes night and day.

3. Revolution Earth’s movement around the sun is a revolution.
1 complete revolution = 1 year = days

4. The Seasons
Equator does not experiences difference in temp. and daylight in seasons because it receives the most direct sunlight.
Poles = extreme temp. differences.
Winter in Alaska = 2 hrs of daylight, in summer = sun never sets.
Seasons caused by the tilt of the Earths axis – tilted 23.5 degrees

5. June in the Northern Hemisphere
Axis tilted towards the sun.
Summer – longer days, warmer temperatures
NOT caused by the distance from the sun, caused by more direct sunlight.

6. December in the Northern Hemisphere
Earth’s axis pointed away from the sun.
Winter = shorter days, colder temperatures, due to less direct sunlight and fewer hours of daylight.

7. Misconception
Seasonal differences are NOT caused by changes in the distance from the sun. They are caused by changes in the amount of direct sunlight due to the 23.3* tilt of Earth’s axis.

8. June and December Solstice
June 21st =
Summer Solstice
Longest day of the year, considered first day of summer.
December 21st =
Winter Solstice
Shortest day of the year, considered first day of winter.

9. March and September Equinox
Equinox is halfway between each solstice.
Equinox – neither hemisphere is pointed towards or away from the sun.
Equinox (equal night) 12 hrs day/12 hrs night
March 21st – spring equinox,
September 22nd – fall equinox.

10. BRAINPOP

11. Gravity and Motion
Recall that gravity is a force that attracts all objects towards each other.
Universal Law of Gravitation – every object in the universe attracts every other object.

12. Gravity and Motion
The strength of gravity is dependent on 2 things: the mass of the objects, and the distance between them.
If mass increases, gravity increases.
If distance increases, gravity decreases.
Weight – the force of gravity on an objects mass.

13. Inertia and Orbital Motion
Two factors keep Earth and the moon in their orbits – inertia and gravity.
Earth’s gravity pulls the moon toward it, preventing the moon from traveling in a straight line. The moon keeps moving ahead because of its inertia.

14. Inertia
Inertia is the tendency of an object to resist a change in motion.