Assumed Preparation: This lesson is based around the activities and questions outlined in Worksheet 5 in the Teachers Guide for Everyday Einstein: GPS and Relativity. It is assumed that students have already studied gravity, orbital motion and inertial frames of reference. It would be benefitial but not necessary if the students had already studied special realtivity.
Subversive Physics: General relativity is not an explicit part of any high school curriculum, so how can you justify spending time on the equivalence principle? An exploration of the equivalence principle is a natural fit in a unit dealing with frames of reference and fictitious forces. It also could be included when dealing with changing models in science. If your curriculum deals with special relativity, you could include a brief comparison of special and general relativity. Each theory started with simple assumptions and explored their consequences for light and time.
The Activity: The students explore the consequences of the equivalence principle through a couple of activities and a set of concept questions and small group discussions. You will need to firmly attach strings to a tray (or better yet, many trays) so you can place a glass of water on it and swing it around. You will need to have a bottle of water with a hole drilled into the lid. You will also need a class set of the questions in worksheet 5. If your class enjoyed this lesson, why not go to the next one 2) General Relativity: Gravity Curves Light.
Further Information:
The best site for information about relativity is Einstein Online. http://www.einstein-online.info/elementary/generalRT.
Take a look at the extra notes in the Teacher`s Guide for Everyday Einstein. It discusses the equivalence principle in more detail and it also describes another way to develop the gravitational red-shift using conservation of energy.
The Perimeter Institute has a number of one-minute cartoons that can help with orbiting and the equivalence principle. They are the Alice and Bob cartoons: “Why doesn’t the moon fall down?” and “What keeps us stuck to Earth?” and "Can we travel through time?" http://www.perimeterinstitute.ca/en/Outreach/Alice_and_Bob_in_Wonderland/Alice_and_Bob_in_Wonderland/