Galaxies and Dark Matter

This video lesson has the goal of introducing students to galaxies as large collections of gravitationally bound stars. It explores the amount of matter needed for a star to remain bound and then brings in the idea of Dark Matter, a new kind of matter that does not interact with light. It is best if students have had some high school level mechanics, ideally Newton's laws, orbital motion and centripetal force. The teacher guide segment has a derivation of centripetal acceleration. This lesson should be mostly accessible to students with no physics background. The video portion of this lesson runs about 30 minutes, and the questions and demonstrations will give a total activity time of about an hour if the materials are all at hand and the students work quickly. However, 1 1/2 hours is a more comfortable amount of time. There are several demonstrations that can be carried out using string, ten or so balls of a few inches in diameter, a stopwatch or clock with a sweep second hand and some tape. The demonstrations are best done outside, but can also be carried out in a gymnasium or other large room. If the materials or space are not available, there are videos of the demonstrations in the module and these may be used.
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