1. Motion of Objects in Space

2. Models of the Solar System
A) Aristotle ( BC):
Greek astronomer that believed that the Earth was motionless and at the center of the universe.
This became known as the earth centered or geocentric model.

4. B) Nicolas Copernicus (1473 - 1543):
Concluded that the Earth is a planet.
Proposed a model of the solar system with the Sun at its center.
In the Heliocentric Model, Earth and the other planets orbit the Sun.
His model used circular orbits not ellipses.

6. C) Johannes Kepler ( )

7. Kepler’s First Law
The orbits of the planets around the Sun are ellipses, with the Sun at one of the foci.

8. Kepler’s First Law

9. What is an Ellipse?
Earth’s orbit is slightly elliptical

10. Ellipses have 2 foci
Circles have 1 focus
An ellipse is basically a stretched out circle

11. The circle is becoming more oval.

12. Formula for Eccentricity on pg. 1 of R.T.
Distance between foci
________________
Length of major axis

13. Steps for determining eccentricity
1st measure the distance between the 2 foci (the sun is usually at one of the foci)
2nd measure across the entire ellipse (the longest part)
This is the major axis.
3rd Use the formula to calculate eccentricity.
The least eccentric (a circle) has an eccentricity of 0 – not eccentric. The most eccentric (a line) has an eccentricity of 1.

14. There are no units for eccentricity
Number has to be written out to the thousandths place

15. How to draw an Ellipse

16. Ellipse vs. Circle Animation

17. According to the ESRT, which planet has the most eccentric orbit?
Mercury
Which planet has the least eccentric orbit?
Venus

18. Kepler’s Second Law
Planets sweep out equal areas in equal periods of time

19. This is because when the planet is closer to the Sun, (perihelion), it speeds up, and when it is further away from the Sun, (aphelion) it slows down

20. Kepler’s Second Law
30 days
30 days

21. Kinetic vs. Potential Energy
What is kinetic energy?
Energy of motion. Objects moving faster have more kinetic energy than objects that are moving slow. Objects that are not moving do not have any kinetic energy.
What is potential energy?
Stored energy. Energy based on position. An object at the top of a hill and not moving has more potential energy than an object at the bottom of a hill and not moving.

22. Kepler’s Second Law Animation
Faster
Slower
Greatest potential energy – farthest from the sun. Least KE.
Greatest kinetic energy – closest to the sun. Least PE.

24. Kepler’s Third Law
A planet farther from the Sun not only has a longer path than a closer planet, but it also travels slower, since the Sun's gravitational pull on it is weaker.

25. Therefore, the larger a planet's orbit, the longer the planet takes to complete it.
According to the ESRT, which planet has the longest period of revolution?
Neptune – years

26. What is the force of attraction between all objects?
Gravity!

27. How do planets stay in their orbits?
Gravity is a strong attractive force between objects

28. The more massive two objects are, the greater the gravitational force between them
The closer the two objects are to each other, the greater the gravitational force between them

29. Therefore..
As planets move closer to the Sun, their orbital velocity (speed) increases

30. mass

31. Inertia:
Earth does not get pulled into the Sun because of Inertia

32. An object in motion will continue moving in a straight line at a constant speed unless acted upon by a force – GRAVITY!

33. Principle of Inertia