Welcome to the Neighborhood

1
Welcome to the Neighborhood

• Our Solar System

2
Whats the difference between rotation and
revolution?

• Each planet spins on its axis.
• This spinning is called rotation.
• Q How long does it take the Earth to rotate on
  its axis once?
• A Approximately every 24 hours. This is equal
  to one day.

3
Whats the difference between rotation and
revolution?

• Q How much of the Earth is facing the sun at any
  time?
• A Half of the Earth faces the sun
• Half of the Earth has day and the other has
  night.

4
Whats the difference between rotation and
revolution?

• Q What is the path that one body follows as it
  travels around another body is space is called?
• A Orbit
• One complete trip along an orbit is called a
  revolution.

5
Whats the difference between rotation and
revolution?

• Q Do all planets in our solar system have the
  same period of revolution?
• A No!
• Q Which planet do you think has the shortest
  period of revolution? Longest?

6
Whats the difference between rotation and
revolution?

• Q How long is Earths period of revolution (or
  the time it takes Earth to orbit or revolve
  around the sun once)?
• A One year 365.25 days

How many revolutions have you made around the sun?
7
Review

• Rotation the spin of a body on its axis
• Orbit the path that a body follows as it
  travels around another body in space
• Revolution the motion of a body that travels
  around another body in space one complete trip
  along an orbit

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Johannes Kepler (1571 1630)

• German astronomer
• Influenced by the Copernicus
• Professor of mathematics
• Contemporary of Galileo
• Described the orbit of Mars
• He wrote three laws that are important to
  astronomy and are known as Keplers Laws

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Keplers Laws

• Planets orbit the sun in an elongated circle
  called an ellipse
• Planets move faster when they are closer to the
  sun, and slower when they are further away
• Planets that are closer to the sun orbit faster
  than planets farther away

10
Sir Isaac Newton (1642 1727)

• Newton was born in England the same year Galileo
  died.
• He is the most influential scientist who ever
  lived
• He defined the laws of motion and universal
  gravitation which he used to predict precisely
  the motions of stars, and the planets around the
  sun.
• Newton constructed the first reflecting telescope.

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Universal Gravitation

• An objects are attracted to each other because of
  gravity
• This attraction depends on the mass of the two
  objects and the distance between them
• The larger the masses of the two objects and the
  closer they are to each other, the greater the
  force of gravity between them

12
Gravitational force is the dominant force the
determining motions in the Solar System.Gravity
keeps the planets in orbit around the sun.
13

• If gravity pulls objects together, why doesnt
  the moon come crashing into the Earth?

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Orbits Falling Down and Around

• The moon has inertia.
• Newton's first law of motion states that "An
  object at rest tends to stay at rest and an
  object in motion tends to stay in motion with the
  same speed and in the same direction unless acted
  upon by an unbalanced force."
• In other words, objects tend to "keep on doing
  what they're doing."
• This tendency to resist changes in their state of
  motion is described as inertia.

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Orbits Falling Down and Around

• Q There is no air in space. What effect do you
  think this has on the moons inertia?
• A No air no resistance. The moon continues to
  move.

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Orbits Falling Down and Around

• Q But what about gravity?
• A The combination of the moons inertia AND
  gravity is what causes the moon to move in a
  circular path around the Earth.
• Q Is this why we revolve around the Sun in an
  elliptical orbit?
• A Yes!

17
Review
18
Kepler discovered that planets move faster when
they . . .

• A) are farther from the sun.
• B) are closer to the sun.
• C) have more mass.
• D) rotate faster.
• Answer
• B) Planets move faster when they are closer to
  the sun.

19
What is the difference between rotation and
revolution?

• Rotation the spin of a body on its axis
• Revolution the motion of a body that travels
  around another body in space one complete trip
  along an orbit

20
What causes a day?

• The rotation of the Earth once on its axis.
• It is approximately 24 hours.

21
What causes a year?

• The revolution of the Earth once around the sun.
• It is approximately 365.25 days.

22
On what two properties does the force of gravity
between two objects depend?

• Mass (the amount of matter in an object)
• Distance (how far apart they are)

23
What two properties cause an object to have an
elliptical orbit?

• Inertia (an object in motion continues at the
  same speed and direction, unless acted upon by a
  force)
• Gravity (the force that causes to objects to be
  pulled toward each other)

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Homework

• Use pages 630 633 in your text book to complete
  the Guided Reading for this section.
• It is due tomorrow.