Lets talk a little about the energy

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Lets talk a little about the energy of an orbit
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Energy can take on different forms,
light
electrical
chemical
mechanical
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And of course nuclear energy
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Another name for mechanical energy Is kinetic
energy, the energy of motion
Any body in motion has kinetic energy, the
faster it moves, the higher the kinetic energy
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An object not moving at all or moving slowly may
have potential energy, such as a rock on top of a
mountain
High PE
As the rock fall off the cliff PE is converted to
KE
Low PE
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Energy of an asteroid in orbit
downhill
Low kinetic energy
perihelion
aphelion
High kinetic energy
high potential energy
Low potential energy
uphill
KE PE constant
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Watch the comet change speed as it gets further
and closer to the sun
Low Velocity
High Velocity
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As this planet orbits the sun, where will it be
going fastest? Slowest?
B
A
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Gravity

• The force of attraction between
• any two objects in the universe

The MORE MASS the object has, the stronger its
force gravity
The CLOSER the objects the stronger the
attraction between them
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Gravity
Stronger gravitational attraction
Weaker gravitational attraction
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Gravity
Stronger gravitational attraction
Weaker gravitational attraction
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North Pole
Where on earth
here
equator
Would you weigh the most
South pole
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If the sun has so much mass ( strong gravity),
why dont the planets fall into the sun?
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Because of Inertia

• An object at rest will tend to remain
• at rest
• An object in motion will maintain
• its direction and speed unless a
• an opposing force affects is
• (like gravity)

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Newton first explained gravity using the moons
orbit around earth
Solid arrow Earths gravity Dashed arrow
moons inertia
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Inertia gravity
give all objects in the solar system
orbits around the sun
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Do Now

• What two conditions yield the strongest force of
  gravity between two objects in the solar system?
• Why dont the planets fall into the sun?
• What is kinetic energy?
• What is potential energy?
• Where in its orbit is a planet traveling the
  fastest?

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Apparent Diameter

• The size an objects appears to
• be depends on how far away it is.
• Objects far away appear small
• Objects nearby appear big

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What does this suggest about the suns distance?
How large something appears in our Sky is called
the apparent or angular diameter
Yes, the sun is almost exactly 400 times further
away than the moon
The sun is actually 400 times larger than the moon
SUN
By shear coincidence the sun and moon both appear
to have the same apparent diameter as viewed from
Earth
MOON
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What could cause the moon to appear
slightly larger than the sun?
When the moon does appear larger than the Sun, a
total eclipse can occur
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As a result of the earths slightly elliptical
orbit, the sun will appear slightly larger in
January compared with July
Which Sun appears slightly larger?
Photo taken in July
Photo taken in January
In what season would the sun look larger?
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Which photo was taken when Venus was closest to
Earth?
crescent
quarter phase
nearly full phase
How is this evidence that Venus is orbiting the
sun instead of earth?