A. Gravity
1. Newton’s Laws of Motion
a. First Law: An object at rest, or in motion in a straight line at a constant speed, will
remain in that state
... [Show More] unless acted upon by a force
i. Aka. inertia
2. Second Law: The acceleration of a body due to a force will be in the same direction as
the force, with a magnitude inversely proportional to its mass.
a. OR the magnitude of force necessary to produce a certain acceleration on a body
will be directly proportional to its mass
b. A higher mass requires a greater force
c. F = ma or force = mass x acceleration
i. Example: if you apply the same amount of force to a soccer ball and a
car the ball will move faster
3. Third Law: for every action there is an equal and opposite reaction.
a. Example: The sun’s force of gravity keeps the planets in orbit around it
b. The planets exert and equally strong pull on the sun (causes it to move slightly)
4. Newton’s Law of Universal Gravitation
a. All objects with mass experience attraction towards each other as a result of the
gravitational force between them
b. Fg =
𝐺(𝑀1𝑀2)
𝑟
i. Fg: force of gravity
ii. G: universal constant of gravitation
iii. M1: mass of one object
iv. M2: mass of a second object
v. R: distance between the two objects
c. The gravitational force is directly proportional to the mass of each interacting
object and inversely proportional to the distance between them, squared
i. 𝑔 𝛼 𝑚
𝑟
d. the ratio of the gravitational of gravitational accelerations experienced by a person
or object on two different planets
i. gÆ
g𝐵
(
𝑚𝐴
)
= 𝑚𝐵
r𝐵
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e. when you take the ratio of the gravitational accelerations experienced by two
objects of different masses being influenced by a third body, their values of g
are the same
i. the strength of the gravitational force between higher-mass objects is
greater than for lower masses, it requires a greater force to be applied
to have the same overall acceleration
5. Gravity Game
a. strength of a gravitational field depends on the planet’s mass and radius.
b. As the mass of the planet increases, the jump height decreases by the same factor
as the mass
c. The mass of the planet and the jump height are inversely related
d. As the radius of the planet increases, the jump height increases as the square of
the radius.
e. Gravity is inversely proportional to the square of the radius
B. Seasons
1. Affected by the Earth’s tilt with respect to plane in which they orbit the Sun
a. No tilt = no seasons
b. Mars (25 degrees) and Earth (23 degrees) have almost the same tilt
c. Ex: when it is summer in the Northern hemisphere it is winter in the Southern
hemisphere
2. “1 AU” (astronomical unit) is the distance from the center of the Earth to the center of
the Sun.
a. about 150 million kilometers (93 million miles)
3. changes in the distance from the Sun during a year are not significant factors in
changing temperatures on planets because most planets’ orbits are nearly circular
4. perihelion: point in the orbit of an object that is closest to the sun
5. aphelion: point in the orbit of an object that is furthest from the sun
a. March 21st and September 21st are days of the year where both day and night are
exactly twelve hours everywhere on Earth
b. June 21st and December 21st are the longest and shortest days of the year
respectively
6. June 21st
= Summer Solstice
a. Northern hemisphere tilted toward Sun
7. December 21st
= Winter Solstice
a. Northern hemisphere tilted away from Sun
C. Phases of the Moon
1. Each day, the Moon does not move very far along its orbit
a. Its orbit is tilted with respect to the Earth
2. The Moon is tidally locked to the Earth, so the same side is always facing us
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3. Completes one set of phases over the course of about one month
a. About two phases a week
4. Just like the Sun, the Moon rises in the east and sets in the west
a. Due to the rotation of the Earth
5. The moon orbits the Earth, and this is the key for the moon’s phases
a. The rotation of the Earth= 1 day, the orbit of the Sun by the Earth= 1 year, the
time it takes the moon to orbit the Earth= 1 month (1 “month”) or 27-30 days
6. Phases result from changes in the relative positions of
a. the Moon
b. the Earth, or a viewer on the Earth’s surface
c. the Sun
7. phases are determined by the fraction of the illuminated portion of the Moon’s surface
visible from Earth
8. The Moon is always 50% illuminated
a. What we see on Earth is just a fraction of that half
i. Ex: we see all of the 50% when there is a full moon
ii. Ex: we see half of the 50% when the Moon is in its first or third quarter
phase
9. Full Moon: Earth is in a direct line between the Sun and Moon
a. The moon is fully lit up, therefore completely visible to us
b. Overhead at midnight
10. New Moon: Moon is between the Sun and Earth
a. Overhead during the day but it is obscured by the brightness of the sun so it is not
visible to us
b. Overhead at noon
11. First Quarter Phase: mid-way between a new moon and a full moon
a. One of the two “half moon” phases
b. Sees the right half of the moon lit up
c. Seen overhead at 6pm
12. Third (or Last) Quarter Phase: after the full moon, mid-way to the next new moon
a. One of the two “half moon” phases
b. Sees the left half of the moon lit up
c. Seen overhead at 6am
13. Waxing: Moon will be MORE illuminated in the coming days
a. Advancing toward Full Moon
14. Waning: Moon will be LESS illuminated in the coming days
a. Advancing toward New Moon
15. Gibbous: Phase of the Moon when all is illuminated EXCEPT for a crescent
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