19. one point, from Lectures 18 and 19, a group question, explanations, pictures, pretty hard

(a) .2 It's All in Your Head! What is a ``Gedanken'' experiment (.1), and when do physicists need to do one? (.1)

(b) .4 Simultaneity is Relative. Explain the Gedanken Experiment in the Albert--Henry video which shows that simultaneity is relative. (.4) You must start your explanation from Einstein's Second Postulate. While this might be easier with pictures, even then it's hard, so DON'T use pictures. Do not use the book or lecture examples; use the video example.

(c) .4 Moving Length is Relative. Contrast the examples from the lecture (.2) and the book (pp. 109-111) (.2) which were used to show that a moving train is measured to be shorter than a train at rest. You must be very clear on what is different between the two presentations. I prefer my way of doing it to the book's, but I want to know which way you think works better. Please say which way you prefer and why. Do not draw pictures.

Revised October 19, 1997.