1. Gravity & Motion
Astronomy

2. Kepler’s Laws of Motion
First- Planets move in elliptical orbits around Sun
Foci- Two fixed points in an ellipse
Major axis- Maximum diameter of ellipse
Semimajor axis- Half of major axis
Eccentricity- Ratio of distance between foci and major axis
Perihelion- Planet is nearest Sun
Aphelion- Planet farthest from Sun

3. Second- Planets move like there is an imaginary line connected to the Sun
Third- Squares of sidereal periods of planets is proportional to cubes of semi-major axes
Sidereal period- Time for planet to complete one orbit around Sun

4. Galileo Mathematician by choice
Experimented with gravity by dropping objects
Air resistance determines speed
Once an object is in motion, it will remain in motion unless acted upon

5. René Descartes Believed that all changes in motion due to “corpuscles”
Inertial motion- Motion when there are no unbalanced forces acting on object

6. Early planetary motion
Aristotle & Ptolemy- planetary bodies located on crystalline spheres
Robert Hooke- knew about Sun’s force on planets
Central force- Force acting on a center of motion

7. Gravity
What is gravity?

9. Sir Isaac Newton
Brilliant man with numerous discoveries, but needed a little push
Wrote Principia about planetary orbits and gravity
Newton’s three laws:

10. Law of Inertia
An object at rest remains at rest unless acted upon by unbalanced force
Inertia- Resistance to changes in motion
Velocity- Speed and direction of an object
Acceleration- rate velocity changes with time
Mass- Measure of inertia of a body
Momentum- Mass multiplied by velocity (direction & magnitude)

11. Law of Force
When an unbalanced force acts upon an object, it produces a change in momentum in the direction in which the force acts
Force- A push or pull

12. Law of Action & Reaction
When one body exerts a equal and opposite force on another body, the second body also exerts a force on the first.

13. Orbital Speed and Energy
Kinetic energy
Gravitational potential energy

14. Tides Distortions in shape resulting from tidal forces
Tidal forces- differences in gravity in an object being attracted to another
Solid Earth (Terrestrial) tides- Distortion due to moon & Sun
22 inches at equator (5.9 in due to Sun)
Generate currents in conducting fluid within Earth [magnetic field]
Ocean tides- Tidal acceleration causes vertical and horizontal movement
Spring- Unusually high or low
Neap- Weak tides

15. The day gravity reversed itself…