Announcements 11/30/11

Prayer Henry Lorentz Exam 3 ongoing… Project Show & Tell. Email me by tonight (midnight). I

will pick people tomorrow and let you know who the winners are. Reminder: +3 pts for volunteering, +6 more if selected

All late homework & extra credit papers due Fri, Dec 10. Earlier if possible!

Office hours: a. Today: Colton none; Chris 5-7 pmb. Friday: Colton none; Chris 2:30-5 pmc. Monday: Colton regular; Chris regulard. Wed: Colton none; Chris 5-7 pm Find me in my lab if needed, U130

Frank &Ernest

Space-time diagrams

Example: me slamming the book on the table

Example: me slamming the book on the table again

Example: measuring the time between book slams

Example: measuring the length of the book

“World lines” for Dr. Colton, book, & for space traveler passing by earth

a. When/where do these events occur?

t vs. ct

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:

a. The planet Earthb. The planet Zyzyxc. Dr Colton, as he travels to Zyzyxd. 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.

Light cones

Present Possible futures Possible pasts “Elsewhere” Terminology: “timelike” vs “spacelike”

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. Draw the light from the flashlight. Mark the “flashlight turned on” event.

Do this for both frames of reference.

Reading Quiz

The Lorentz transformation equations in the book assume objects only have relative motion in the +x or –x directions

a. Trueb. False

The Lorentz transformation equations in the book given for y and z are more complicated than the equations for x and t.

a. True b. False

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

The Lorentz Transformations

As regular equations:

In matrix form:

frame2 frame1 frame1( )x x ct

frame2 frame1 frame1( ) ( )ct x ct

frame2 frame1

x x

ct ct

Differences between my equations & book’s equations

Disclaimer: I often reverse order of x and ct in matrix eqn. That’s OK.

Lorentz transformations, graphically

Lee’s program Similarity with 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.