1. Charles Hakes
Fort Lewis College 1

2. Chapter 1
Newton
and Gravity
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3. Outline Notes Kepler Review Newton’s laws Gravity
Tutoring… Berndt 610, 640 late afternoons (Katy, Shane, Luke)
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4. Review African or European? Other favorite answers…
The speed of light.
I don’t know - I’m not king!
My Holy hand grenade blew it up
“42”: (mixing your fiction).
I’m from Oklahoma and have no clue
… for a chimney swallow while hunting mosquitoes….
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5. Group Exercise
Assume a comet has a period of 5.2 years, with eccentricity very close to 1.
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6. Group Exercise
Assume a comet has a period of 5.2 years, with eccentricity very close to 1.
Calculate the semi-major axis.
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7. Group Exercise
Assume a comet has a period of 5.2 years, with eccentricity very close to 1.
Calculate the semi-major axis.
p2 = a3
What is the major axis?
What is the maximum distance this comet might ever get from the Sun?
Include copy of work in your folder.
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8. Figure 1.20 Isaac Newton (1642-1727)
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9. Which hits the ground first?
An iron weight and a styrofoam ball are dropped from the same height at the same time.
Which hits the ground first?
A) The iron weight
B) The styrofoam ball
C) They hit at the same time
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10. Newton’s “Laws”
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11. Newton’s 1st Law If there are no external forces on an object, then:
If it is at rest, it will stay that way - forever.
If it is moving, it will keep doing so at constant velocity, in a straight line - forever.
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12. Newton’s 1st Law
Inertia - the natural tendency of an object to stay at rest, or remain moving with a constant velocity.
Mass is a quantitative measure of inertia.
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13. momentum = mass x velocity
Momentum - the product of mass and velocity.
momentum = mass x velocity
A concept related to Inertia
Momentum (both linear and angular) must be conserved.
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14. Which object has the most momentum?
A) A cruise missile
B) A ship
C) A glacier
D) Need more information
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15. Which object has the most momentum?
A - A cruise missile
1000 kg
100m/s
B - A ship
10 million kg = 107 kg
10 m/s
C - A glacier
1012 kg
1 m/day (~10-5 m/s)
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16. Which object has the most momentum?
A - A cruise missile
B - A ship
C - A glacier
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17. Angular momentum demonstration
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18. Angular momentum demonstration
This is why planets move faster closer to the sun.
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19. Newton’s 2nd Law Fnet = m a
The net force on an object is equal to the mass of the object times the acceleration of the object
Fnet = m a
The SI units of force are newtons (N).
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20. Newton’s 2nd Law
Force - something that is capable of changing an object’s state of motion (it’s velocity)
Fnet - the sum of all forces on an object
Dynamics - the study of changes in motion and what causes those changes
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21. Newton’s 2nd Law
Fnet = m a
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22. Newton’s 3rd Law …the one hard to believe… Charles Hakes
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23. A brick hits a glass window
A brick hits a glass window. The brick breaks the glass, so the magnitude of the force of the brick on the glass is
A: is greater than the magnitude of the force of the glass on the brick
B: is smaller than the magnitude of the force of the glass on the brick
C: is equal to the magnitude of the force of the glass on the brick
D: none of the preceding
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24. Newton’s 3rd Law
For every action (force) there is an equal and opposite reaction (force).
Important note - the action-reaction force pairs do NOT act on the same object.
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25. A brick hits a glass window
A brick hits a glass window. The brick breaks the glass, so the magnitude of the force of the brick on the glass is
A: is greater than the magnitude of the force of the glass on the brick
B: is smaller than the magnitude of the force of the glass on the brick
C: is equal to the magnitude of the force of the glass on the brick
D: none of the preceding
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26. Gravity
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27. Figure 1.22 Gravity
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28. Figure 1.24 Sun’s Gravity
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29. Gravity
Any object having Mass will exert a gravitational force on other massive objects.
Force is proportional to mass of each object
F  M1 M2
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30. Gravity
Any object having Mass will exert a gravitational force on other massive objects.
Force is proportional to mass of each object
Force decreases with the square of the distance between the two objects
F  M1 M2 / r2
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31. Figure 1.23 Gravitational Force
Any object having Mass will exert a gravitational force on other massive objects.
F  M1 M2 / r2
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32. Gravity
Any object having Mass will exert a gravitational force on other massive objects.
Force is proportional to mass of each object
Force decreases with the square of the distance between the two objects
Proportionality constant is “G”, the universal gravitational constant
G = 6.67x10-11 (N m2/kg2)
F = G M1 M2 / r2
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33. Gravity
F = G M1 M2 / r2
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34. Newton Modification to Kepler’s 1st Law
Both the Sun and the planet orbit about the center of mass of the system.
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35. Figure 1.25 Orbits
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36. P2 (years) = a3 (astronomical units) Mtotal(solar units)
Newton
Modification to Kepler’s 3rd Law
That “math” law - updated
P2 (years) = a3 (astronomical units) Mtotal(solar units)
For planets around the Sun, this makes very little difference except for (even for) Jupiter (0.1% Msun)
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37. Which mass pair has the greatest gravitational force between them?
1: A 5Msolar mass and a 4Msolar mass separated by 4 AU.
2: A 4Msolar mass and a 3Msolar mass separated by 3 AU.
3: A 3Msolar mass and a 2Msolar mass separated by 2 AU.
4: A 2Msolar mass and a 1Msolar mass separated by 1 AU.
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Fort Lewis College 37

38. Which mass pair has the greatest gravitational force between them?
1: A 5Msolar mass and a 4Msolar mass separated by 4 AU.
2: A 4Msolar mass and a 3Msolar mass separated by 3 AU.
3: A 3Msolar mass and a 2Msolar mass separated by 2 AU.
4: A 2Msolar mass and a 1Msolar mass separated by 1 AU.
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39. Group Exercise Calculate the force between those two masses.
A 2Msolar mass and a 1Msolar mass separated by 1 AU.
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40. Three Minute Paper Write 1-3 sentences.
What was the most important thing you learned today?
What questions do you still have about today’s topics?
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41. Review What was the most important thing you learned?
A circle is actually a special kind of ellipse with only one focal point
A square is to a rectangle as a circle is to an ellipse
The semi-major axis is half of the major axis.
If the semi-major axis of two bodies is the same, they take the same amount of time to orbit.
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Fort Lewis College 41

42. Review What was the most important thing you learned?
Planet’s move faster when closer to the sun
The closer the focus points, the more like a circle the orbit becomes.
The eccentricity of the ellipse is the ratio of the distance between the foci to the length of the major axis.
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Fort Lewis College 42

43. Review
Did not get thrown into the abyss. (i.e. Remembered Their Monty Python) = 3 Other memorable answers:
I don’t know - I’m not king!
zero???
My Holy hand grenade blew it up
I’m from Oklahoma and have no clue
… for a chimney swallow while hunting mosquitoes….
Charles Hakes
Fort Lewis College 43