1. “If I have seen farther than other men, it is because I stood on the shoulders of giants” -Isaac newton
CHAPTER

2. 5-1 Galileo and newton
Kepler discovered the 3 laws of planetary motion, but he did not understand WHY the planets move along their orbit.
(Make sure you review and know all 3 laws for the chapter 4 and 5 test!!)
He thought that maybe it was a magnetic force or angels pushing the planets along.

3. 5-1 Galileo and newton
Newton was born in England- the year Galileo died
He refined Kepler’s model of planetary motion, but did not perfect it
Newton discovered gravity (the concept of), but did not understand what gravity was.

4. 5-1 Galileo and newton
Aristotle- 4 elements Earth, Water, Air and Fire
Believed objects fall downward because they are moving toward their proper place.
Called these motions natural motions vs violent motions, push and object and make it move other than its proper place.

5. 5-1 Galileo and newton
Galileo- before building his first telescope he studied motion and conducted his own experiments.
Dropping objects- he found the velocities were so great and the time it took the object to drop was short, it was difficult to measure accurately.
rolling balls down a gently sloping incline- found bodies do not fall at constant rates, but are accelerated
Objects move faster with each passing second (9.8m/s)= Acceleration of gravity

6. 5-1 Galileo and newton
Apollo 15 astronaut David Scott

7. 5-1 Galileo and newton
Galileo – noticed that object going down an incline accelerated, while objects going up an incline decelerated
“any velocity once imparted to a moving body will be rigidly maintained as long as the external causes of acceleration are removed”- law of inertia

8. Newton’s 3 laws of motion
5-1 Galileo and newton
Newton’s 3 laws of motion
1) a body continues at rest or in uniform motion in a straight line unless acted upon by some force
Astronauts drifting in space will travel at constant rates in straight lines forever if no forces act on them
Objects continue to move because they have momentum (a measure of its amount of motion) = velocity x mass

10. 5-1 Galileo and newton Newton’s 3 laws of motion
2) The acceleration of a body is inversely proportional to its mass, directly proportional to the force, and in the same direction as the force
F=ma
F= force
m= mass (measure of the amount of matter)
a= acceleration (change in velocity)
Velocity= directed rate of motion (speed with direction)

12. Newton’s 3 laws of motion
5-1 Galileo and newton
Newton’s 3 laws of motion
3) To every action, there is an equal and opposite reaction
Forces must occur in pairs directed in opposite directions.

13. 5-1 Galileo and newton
Newton wondered if the force that holds the moon in its orbit could be the same force that causes apples to fall --- gravity
Inverse square law- strength would decrease as the square of the distance increased (gravitation pull is weaker the farther away the object is)

14. 5-1 Galileo and newton
If Earth pulls on the moon then the moon must pull on Earth. (mutual gravitation)
F= - GMm r2
G= gravitation constant
R= distance between the
masses
M= mass of object 1
m= mass of object 2

15. 5-2 Orbital motion and tides
How gravity pulls on an object
1) An object orbiting Earth is actually falling towards Earth’s center- misses Earth because of its orbital velocity
2) objects orbiting each other actually revolve around their center of mass
3) closed orbits vs open orbits- need enough velocity to follow an open orbit

17. 5-2 Orbital motion and tides
Circular Velocity- lateral velocity the object must have to remain in circular orbit
Earth’s gravity extends to infinity
Escape velocity- velocity required to escape from the surface of an astronomical body
The escape velocity from Earth is about 25,000 miles/hr

19. 5-2 Orbital motion and tides
Affected by how gravity pulls on different parts of an object
Tides are caused by small differences in gravitational forces

20. 5-2 Orbital motion and tides
The side of Earth facing the moon is about 4000 miles closer to the moon than is the center of Earth
Moons gravitation pull is slightly stronger when it acts on the near side vs the center
This creates a bulge on the near side

22. 5-2 Orbital motion and tides
The ocean tides are caused by the accelerations Earth and the oceans feel as they move around that center of mass
As Earth turns it carries you into a tidal bulge, the water deepens as it moves away from the bulge, the water becomes shallow
Bulges are on opposite sides of the Earth
The tides rise and fall twice a day

23. 5-2 Orbital motion and tides
Spring tides- occur 2 x a month during a new and full moon- strong pulls
Neap tides- weaker pulls

24. 5-3 Einstein and relativity notebook page 52
Special relativity
First postulate:
definition
Ex:
Second postulate:
The General Theory of Relativity
General theory of relativity
Equivalence principle
Gravity according to general relativity