## Physics 109n Pledged Homework #1

Due Thursday, October 10, 1996

ANNOUNCEMENT: Tonight, October 1, PBS is running a two hour special about Einstein on NOVA. You should watch it, or tape it to view later.

NOTE: Clarity of presentation, in both words and diagrams, should be your aim here. Answers don't have to be very long, just cover the essential points. Figures should be easy to interpret.

1. Show on a diagram the relative positions of earth and sun when it is winter here, and when it is summer here. Make clear how this relates to the earth's position.

2. Wood floats in water. How was this explained by (a) Aristotle, (b) Archimedes (and Galileo)?

3. Explain with a diagram in the Copernican scheme why Mars sometimes seems to be going backwards in its journey through the Zodiac.

4. Bruno was burned at the stake in 1600 for suggesting there were infinite numbers of inhabited worlds. Why was this idea more plausible after Copernicus than before?

5. Suppose an astronaut is walking around on the moon in the middle of a vast flat plane. How far away is the horizon?

6. Galileo states in Two New Sciences:
"A small dog could probably carry on his back two or three dogs of his own size; but I believe a horse could not carry even one of his own size."
Explain the point Galileo is making here in terms of scaling.

7. Sorry about the eclipse! Here was the announcement from the Washington Post. What is wrong with their diagram of the earth's shadow creeping over the moon?

8. If you had been able to see the eclipse, you would have noticed a bright star very close to the moon - actually, the planet Saturn. Can you figure out from that whether the earth is closer to Saturn than its average distance, or further away? (Hint: draw a Copernicus-like diagram showing the orbits of earth, moon and Saturn, and put the moon in the right place for an eclipse.)

9. Why was Galileo particularly anxious to give an explanation of the tides?

10. Considering how high he claimed the mountains were on the moon, how did Galileo account for the fact that the moon looks so round? Why isn't it jagged? Were his explanations correct?