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Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

Jan 01, 2016

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Rudolph Cannon
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Page 1: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.
Page 2: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

Planets move through the sky withMore complicated paths than

Stars do.

We begin with Kepler’s Laws inOrder to find out how.

Page 3: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

Kepler’s Laws of planetary motionAre stated as…

1)The paths of planets are ellipses,With the sun at one focus.

2) An imaginary line from the sun To a planet sweeps out equal Areas in equal time intervals.

Thus planets move faster when They are closer to the sun, and

Vise-versa.

Page 4: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

3) The square of the ratio of the Periods of any two planets Revolving about the sun is

Equal to the cube of the ratioOf their average distances

From the sun.

TA

TB

=rA

rB

2 3

Page 5: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

TA

TB

=rA

rB

2 3

T = the planets’ periods Of revolution

r = the average distanceFrom the sun (or another focus)

Page 6: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

The first 2 laws apply to each Individual planet, moon, or

Satellite.

The 3rd law relates to the motionOf several satellites about a

Single body.

Page 7: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

Io has a period of 1.8 days and is4.2 units away from Jupiter.

Callisto has a period of 16.7 days.What is the distance away

From Jupiter?

rc = 19 units

Page 8: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

The moon has a period of 27.3 Days and a mean distance fromEarth of 3.9 X 105 km. Find thePeriod of a satellite that is in

Orbit 6.7 X 103 km.

88.6 mins

Page 9: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

Newton also played around With a few formulas for gravitation.

Newton said that there was an Attractive force between

All objects, this is called theGravitational force.

Page 10: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

Newton was so confidant thatHe came up with a law to find

The quantity of gravity.

The Law of Universal Gravitation

F = GmAmB

d2

Page 11: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

F = GmAmB

d2

m = mass

d = distance between The center of the objects

G = 6.67 X 10-11 Nm2 / kg2

Page 12: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

Without showing all the math,The force equals something else.

F = mp4π2r

T2= G

msmp

d2

And rearranged again…

T2 = 4π2

Gmsr3

Page 13: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

Jeff (75 kg) and Racheal (60 kg)sit about 4 Meters away

from each other. Racheal looks up and feels an

Attraction. Find the gravitationalForce between them.

F = 1.87 X 10-8 N

Page 14: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

An object that is falling at theSame rate at which the earth is

Curved is said to be in orbit.

Page 15: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

For an object to be in orbit, air resistance Must be taken away,

which Means that it must be at least 150 km

above the earth.

Use Newton’s thought experimentOn page 179 to see how.

Page 16: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

We can continuously derive New formulas to find out things.

v = GmE

r

T = 2πr3

GmE

These formulas only Work for the earth.

Page 17: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

A satellite orbits Earth 225 km Above its surface. What is itsSpeed in orbit and its period?

v = 7760 m/s T = 1.5 hr

Page 18: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

As you move farther from Earth’s Center, the acceleration due

To gravity changes.

a = grE

d

2

Page 19: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

There are 2 kinds of mass…

Inertial mass And

Gravitational mass

Page 20: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

Inertial mass is a measure of anObject’s resistance to an type

Of force.

minertial = Fnet

a

Page 21: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

The gravitational mass is the sizeOf the gravitational force

Between the objects.

mgrav = r2Fgrav

Gm

Page 22: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

Einstein proposed that gravityIs not a force, but an effect

Of space itself.

According to Einstein, massChanges space itself,

Making it curved.

Page 23: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.

Bodies are thus acceleratedBecause they follow this

Curved space toward the center.

This is Einstein’s Special Theory of Relativity.

Page 24: Planets move through the sky with More complicated paths than Stars do. We begin with Kepler’s Laws in Order to find out how.