APOD: Scale of Earth-moon system and a Saturn-moon system

Earlier this semester, we studied the true scale of the Earth-moon system. It is tough to get a good photo of Earth and our moon together, but here is one of Saturn and one of its moons, Tethys, that little blip halfway out and below the rings. Click for full size view. Again, it is plain to see that a moon and its planet are very different sizes. Excellent.

Caught nappin'

Take a look at the Lecture Files in Webcourses. There is a file for exercise 10, p. 73, which we were working on at the end of lecture. I made an error in the orbital speed computation, which was spotted by Morris and Katherine. The new lecture file for exercise 10 has the correct computation, along with some comments on the law of universal gravitation in chapter 5.

Gracias, Katherine and Morris!! I was nappin'!!

HW 3 is now ready to go.

I just finished setting up HW 3, which goes over some of the concepts in our computation of the acceleration of skateboarder Alan in Thursday's lecture. It also refers to the data set, which I typed up and posted - so that you can double check your own lecture notes.