Assumed Preparation: This lesson assumes that the students have already gone through the activities and questions outlined in Worksheet 5 in the Teachers Guide for Everyday Einstein: GPS and Relativity. That worksheet deals with General Relativity: Gravity Slows Time. The questions in this worksheet review and extend the implications of the equivalence principle. It introduces the idea that the equivalence principle can be used to predict that a beam of light will bend in a gravitational field and that the equivalence principal can’t deal with non-uniform gravitational fields. A full treatment of gravity needs the concept of curved spacetime.
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 set of concept questions and small group discussions. You will need the student worksheet and the teacher's version with answers. You will need about 60 minutes to go through the whole sheet but you could reduce this by choosing specific questions. In particular, questions 3-5 use the equivalence principle in the same way as questions 4-6 in worksheet 5. If your class enjoyed this lesson, why not do the next one 3) General Relativity: Gravity Curves Spacetime.
Further Information:
The best site for information about relativity is Einstein Online. http://www.einstein-online.info/elementary/generalRT.
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/