1. Chapter 3: “Orbits & Gravity"”
Tycho Brahe ( )
Established Observatory of North Sea Island of Hven.
Compiled 20 years of astronomical observation.

2. Chapter 3: “Orbits & Gravity”
Invited Johann Kepler to join him in analyzing his astronomical data just before his death.

3. Tycho Brahe’s Observatory at Uraniborg

4. Chapter 3: “Orbits & Gravity”
Johan Kepler ( )
He developed the Three Laws of Planetary Motion

6. Chapter 3: “Orbits & Gravity”
Law 1: Law of Ellipses
Planets orbit Sun in ellipses not circles with Sun at one focus of the ellipse.

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Law 2: Law of Equal Areas
The straight line joining a planet and the Sun sweeps out equal areas of space in equal intervals of time.

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Law 3: The Law of Periods
A planet’s distance from the Sun is related to its period of revolution. The farther a planet is from the Sun the longer it takes to go around the Sun.

11. Chapter 3: “Orbits & Gravity”
Isaac Newton ( )
Isaac Newton was born 11 months after Galileo died.

13. Chapter 3: ”Orbits & Gravity"
Among his achievements are:
His work entitled Principia formulated the laws of motion that are the basis of mechanics.
It is probably the greatest scientific work ever written. He therefore explained why the planets follow Kepler’s Laws.

14. Chapter 3: ”Orbits & Gravity"
Isaac Newton ( )
He showed that gravity not only makes an apple fall to the ground but also governs the motions of planets and their satellites, and should apply to any bodies (for example, binary stars).

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Isaac Newton gave us the Three Laws of Motion.

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Law #1: A body continues at rest or in uniform motion in a straight line unless acted on by some net force.
Chapter 3: “Orbits & Gravity”

18. Law #2:
The acceleration of a body is
inversely proportional to its mass
directly proportional to the net force and
in the same direction as the force.

19. Law #3: To every action there is an equal and opposite reaction.

20. Chapter 3: "Orbits & Gravity”
Newton’s Law of Universal Gravitation F = GMm/r2 The Gravitational Force between two objects is equal to the Gravitational Constant times the product of their masses divided by the square of the distance between them.

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In regard to orbital motion
An objects circular velocity is the lateral velocity it must have to remain in orbit.
A satellite remains in orbit around Earth by traveling at a circular velocity of 17,400 mph.
If an object accelerates to its escape velocity, the object will leave its orbit and Earth’s gravitational field.
In a geosynchronous orbit an object remains over the same spot on Earth.

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Einstein & Relativity Albert Einstein ( )

24. The Special Theory of Relativity:
Postulate 1:
All motion is relative.
An observer can never detect their uniform motion except relative to mother objects. There is no such thing as absolute rest.
Another way to state Postulate 1 is …The laws of Physics are the same for all observers no matter what their motion so long as they are not accelerated.

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Postulate 2:
The velocity of light is constant and will be the same for all observers independent of the motion independent of the motion of the observer.

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When we think of very large distances or great velocoties Einstein discovered that Newton’s Laws of Motion did not apply.
The mass of an object increases as the velocity of that object approaches the speed of light.
As speed increases, time slows down. This effect is known as time dilation.

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The General Theory of Relativity
This theory contained a new description of gravity. It concluded that gravity, inertia and acceleration are all associated with the way space and time were related.
A gravitational field is a curved region of space-time.

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We feel gravity because Earth’s mass causes a curvature of space time. All masses cause curvature in space-time. The larger the mass the greater the curvature.