1. Explain the meaning of "inverse square law".
2. Discuss each of Kepler's 3 laws.
3. At what point in its orbit is the Earth closest to the Sun?
4. At what point in its orbit is the Earth moving fastest?
5. What causes seasons?
6. What is a semi-major axis of orbit (a)?
7. What is an Astronomical Unit (AU)?
8. Consider Jupiter. It's orbit is 5 AU in size (roughly). How long should it take Jupiter to orbit the Sun once? Show how this calculation would be done.
9. What is the period of Earth's orbit around the Sun?
10. What is the size of Earth's orbit (in AU)?
11. When you stand on the Earth's surface, you experience your "normal" Earth weight. What would happen to your Earth weight if you were one Earth radius above the surface? (That's twice as far from the center as simply standing on the surface.)
12. What does gravitational force between 2 objects depend on?
Some questions from Newton's laws:
13. A 10-kg object is pushed on by a 200-N force. What will be the acceleration?
14. What is the weight of a 100-kg man?
15. Would the answer to 3 be different if he was on the moon? How so?
16. Consider yourself standing on a scale in an elevator. The scale reads your weight. Compared to being at rest, how would the scale reading change (if at all) if the elevator were:
A. Moving with constant velocity upward
B. moving with constant velocity downward
C. Moving with constant acceleration upward
D. Moving with constant acceleration downward
E. If the cable snapped (yikes!) and the elevator were falling
(Answers below.)
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1. Explain the meaning of "inverse square law".
The force (of gravity, in this case) gets progressively weaker by the factor 1 over the distance squared. Double the distance --> force is 1/4 as great as it was. Triple the distance --> force is 1/9 the original.
2. Discuss each of Kepler's 3 laws.
See notes.
3. At what point in its orbit is the Earth closest to the Sun?
Perihelion, which is approximately January 3 each year.
4. At what point in its orbit is the Earth moving fastest?
Same point as 3 above.
5. What causes seasons?
Tilt of Earth's axis.
6. What is a semi-major axis of orbit (a)?
Half the longest distance across the orbital path (ellipse).
7. What is an Astronomical Unit (AU)?
Defined as the semi-major axis of Earth's orbit - roughly 93,000,000 miles - or half the longest width across Earth's orbit.
8. Consider Jupiter. It's orbit is 5 AU in size (roughly). How long should it take Jupiter to orbit the Sun once? Show how this calculation would be done.
5^3 = T^2
So, T = the square root of 125, or around 11 years.
9. What is the period of Earth's orbit around the Sun?
1 year, or approximately 365.25 days.
10. What is the size of Earth's orbit (in AU)?
Defined as 1 AU.
11. When you stand on the Earth's surface, you experience your "normal" Earth weight. What would happen to your Earth weight if you were one Earth radius above the surface? (That's twice as far from the center as simply standing on the surface.)
1/4 your surface weight.
12. What does gravitational force between 2 objects depend on?
mass of the objects; distance between; a universal (unchanging) constant (G)
13. F = m a
200 = 10 a
a = 20 m/s/s
14. W = m g
W = 100 g = 980 newtons
15. Yes. The weight would be smaller (1/6 as much, since Moon surface gravity is 1/6 that of Earth).
16. a. your regular weight
b. your regular weight
c. greater than your regular weight
d. less than your regular weight
e. zero! (meaning that you are "weightless")
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