BYU A Cappella Jam: Noteworthy, Vocal Point and More!

1. Announcements 11/28/12 • Prayer • Exam 3 ongoing… • BYU A Cappella Jam: Friday, 7:30 pm (doors open at 7 pm). Room 151, Tanner building. Tickets are available at the door for $7 or in advance for $5 (Wilk Center info desk). Come see Noteworthy, Vocal Point, and the other BYU a cappella groups! • Project Show & Tell. Email me by tonight (midnight) if you are interested in sharing your project with class. Reminder: +5 bonus pts • I’ve only had two groups volunteer so far • Term project final report – due Wed Dec 5, midnight • All late homework & extra credit papers due Sat, Dec 8 (2nd reading day). Earlier if possible! Frank & Ernest

2. From warmup Extra time on? Figure 39.13 is difficult for me to understand. Other comments? Why do physicists often use "unity" rather than "one"? Is there any other reason other than to sound cooler?

3. From warmup • The Lorentz transformation equations relate the space and time coordinates of "events". What is an "event"? Give three examples. Event: Something that happens at a particular point in space at a particular moment of time. • Slapping a table • I click my mouse • I stomp my foot on the ground • A firecracker going off • Cracking an egg • a car hitting a wall • lightning striking one side of a railway car • getting out of bed • A book closes • A glass shattering on the ground • An LED going on. • A bunny exploding. (What???) • Note: You could also probably just call an object's motion as the event, but I suppose that's what we'll learn Friday. --NOPE

4. From warmup The Lorentz transformation equations relate the coordinates of events occurring in different "frames of reference". What is a "frame of reference"? Give three examples. Reference frame: any observation point with constant velocity. A boxcar moving close to the speed of light An observer on a constant velocity space-ship Henry Lorentz on a spaceship to the planet Zog. An observer standing still Doctor Colton running with a ladder through a garage

5. Space-Time Diagrams Examples: measuring the time between book slams measuring the length of the book “World lines” for Dr. Colton, book, & for space traveler passing by earth When/where do these events occur? t vs. ct

6. Quick Writing • Back to Dr. Colton’s trip to Zyzyx: Dr. Colton travels at 0.9 c to Zyzyx, 1 light year away. Draw, as accurately as you can, these four world-lines: • The planet Earth • The planet Zyzyx • Dr Colton, as he travels to Zyzyx • Leaving from the Earth at the same time/place, a light beam that travels to Zyzyx • Draw, as accurately as possible, the same four world-lines, from Dr. Colton’s point of view.

7. Light cones • Present • Possible futures • Possible pasts • “Elsewhere” • Terminology: “timelike” vs “spacelike”

8. Example • Dr. Colton, on a fast train, turns on a flashlight at x=0, ct=1. People on the ground watch. Draw worldlines for Dr. Colton and the people on the ground, as well as the light from the flashlight. Mark the “flashlight turned on” event. • Do this for both frames of reference.

9. From warmup The Lorentz transformation equations are given as Eqn 39.11 and Eqn 39.12 (reverse transformation) (8th edition). Why are the equations for y and z so trivial? The motion is only in the x direction, so we don't need to worry about y and z. The equation for x needs to account for length contraction; y and z do not.

10. Lorentz Transformations, derived • Not in this class! :-) • Can be done by using properties we’ve discussed: length contraction, time dilation, gamma factor, basic worldline transformations

11. The Lorentz Transformations • As regular equations: • In matrix form: Differences between my equations & book’s equations Disclaimer: I often reverse order of x and ct in matrix eqn. That’s OK.

12. Lorentz transformations, graphically • Lee’s program • Similarity to rotations • How to choose + vs – Note: for HW problems, you can use Lee’s program to check your answers—but not to DO your problems.