1. Loss of simultaneity
Sally sees the light hit her front and back at the same time. In her reference frame, the lights flashed at the same time (she’s in the middle of them). Bob also sees Sally’s front and back light up together. But in his frame, the left lamp must have flashed first…it had farther to go.
Events simultaneous in one reference frame may not be in another

2. Loss of simultaneity .
Events occurring at the same position (the chair): If simultaneous, then simultaneous in all frames. (Sally and Bob both see her front and back light up at the same time).
Events occurring at two positions (at the lamps): If simultaneous in one frame, won’t be in the other : (They don’t agree on when the lamps flashed)
[The text has this backwards & wrong…it says they can’t agree on if the lights hit Mary simultaneously]

3. Ladder and Garage You can now close both doors!
Your friend is carrying a ladder to your garage. You pushing the door controls. The ladder is too long to fit in the garage. Using relativity, how can you or he make it fit?
You can now close both doors!
(for a little while…you must open the back door soon!)

4. Ladder and Garage Solution?
But from your friend’s point of view, the garage shrinks, making the problem worse! Can he agree that the ladder is inside with both doors closed?
Solution?

5. Ladder and Garage
In your reference frame, the doors are simultaneously closed

6. Ladder and Garage
In your friend’s reference frame, the back door opens before the front door closes. The closing and opening of the doors are not simultaneous.

7. Classical velocity addition: two observers and a third object
The ship’s crew ejects a canister that they see separate from them at 750 m/s (symbol u). The ship is traveling at 500 m/s (symbol v) toward the tracker on earth. What speed does the tracker (u’) see for the can? (Either observer can be the ‘ one).
750
500
These speeds are << c, so we can use the simple classical method u’ = u + v (or u = u’ + v depending on setup)

8. Relativistic velocity addition: two observers and a third object
The ship’s crew ejects a canister that they see separate from them at 0.75 c (symbol u). The ship is traveling at 0.5c (symbol v) toward the tracker on earth. What speed does the tracker (u’) see for the can?
0.75 c
0.5 c
We can’t have u’ = 1.25 c!

9. Relativistic velocity addition: two observers and a third object
The ship’s crew ejects a canister that they see separate from them at 0.75 c. The ship is traveling at 0.5c toward the tracker on earth. What speed does the tracker see for the can?
0.75 c
0.5 c

10. Relativistic velocity addition: two observers and a third object
The ship’s crew ejects a canister backward that they see separate from them at 0.75 c. The ship is traveling at 0.5c toward the tracker on earth. What speed does the tracker see for the can?
0.75 c
0.5 c
Easiest way: work the problem classically, then add the correction, and carry the signs into the correction.

11. Relativistic velocity addition: two observers and a third object
The ship’s crew moving away from earth ejects a canister toward earth that they see separate from them at 0.75c. The ship is traveling at 0.5 c toward the tracker on earth. What speed does the tracker see for the can?
0.75 c
0.5 c

12. Relativity, electricity & magnetism
- charges at rest, + move to right
Sally sees scene 1: a + charge is by a very thin neutral wire that carries a current.
Force on the + charge?
Force on the wire? (ignore polarization)

13. Relativity, electricity & magnetism
Bob moves to the right at v vs Sally and sees scene 2:
the + charges are motionless, but now the – charges are moving.
P3. In the wire Bob sees ____ compared to what Sally sees.
a) +’s more dense and –’s less dense
b) +’s less dense and –’s more dense
The current in the wire is ____ (right/left)
The magnetic field created is _________ at the + charge
a) dots b) crosses
P5. The electric force on the charge is _____a) up b) down
P6. The magnetic force on the charge is _____a) up b) down
The total force is _______

14. Relativity, electricity & magnetism
Relativity is essential to understand how magnetism and electricity interchange in different frames. For the same collection of charges, velocities and charge separations change in different frames, so B and E must change. Even though v is tiny (1-10 cm/sec) in wires, there are so many charges that we see this relativistic effect in everyday life manifest in B and E fields.

15. If this sticker is blue, you're driving too fast.
Doppler shift of light
Bumper sticker:
If this sticker is blue, you're driving too fast.
We can tell galaxies are moving away from us because their spectra are “red-shifted”

16. Decide signs based on toward (frequency goes up), away (goes down)
For light only one v matters:
relative motion v between source and any observer.

17. train video: http://www.youtube.com/watch?v=wteiuxyqtoM

18. P1. Who measures the proper time interval during which the front door is closed?
you
friend
neither
P2. Who measures the proper time interval during which some part of the ladder is inside the garage?
you
friend
neither