Transcript Power Point Presentation

Welcome to the
Neighborhood
Our Solar System
What’s the difference between
rotation and revolution?
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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.
What’s the difference between
rotation and revolution?
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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.
What’s the difference between
rotation and revolution?
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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.
What’s the difference between
rotation and revolution?
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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?
What’s the difference between
rotation and revolution?
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Q: How long is
Earth’s 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?
Review
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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
Johannes Kepler (1571 – 1630)
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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 Kepler’s Laws
Kepler’s Laws
1.
2.
3.
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
Sir Isaac Newton (1642 – 1727)
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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.
Universal Gravitation
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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
Gravitational force is the
dominant force the determining
motions in the Solar System.
Gravity keeps the planets in
orbit around the sun.
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If gravity pulls
objects
together, why
doesn’t the
moon come
crashing into
the Earth?
Orbits Falling Down and Around
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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.
Orbits Falling Down and Around
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Q: There is no air in space. What
effect do you think this has on the
moon’s inertia?
A: No air = no resistance. The moon
continues to move.
Orbits Falling Down and Around
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Q: But what about gravity?
A: The combination of the moon’s 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!
Review
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.
What is the difference between
rotation and revolution?
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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
What causes a day?
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The rotation of the
Earth once on its
axis.
It is approximately
24 hours.
What causes a year?
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The revolution of
the Earth once
around the sun.
It is approximately
365.25 days.
On what two properties does
the force of gravity between two
objects depend?
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Mass (the amount of matter in an
object)
Distance (how far apart they are)
What two properties cause an
object to have an elliptical orbit?
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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)
Homework
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Use pages 630 –
633 in your text
book to complete
the Guided
Reading for this
section.
It is due tomorrow.