1. Unit 9: Special Relativity Lesson 1: The Theory

2. Michelson-Morley Experiment
Purpose: to detect the absolute motion of the Earth through the “aether” (an invisible, non-viscous, and perfectly incompressible fluid filling all of space, through which light-waves were thought to propagate).
Start slide with video (black box). – 10 min

3. And the bottom beam does this:
If the apparatus is moving to the right through the aether (due to the Earth’s motion), then the top beam does this:
And the bottom beam does this:
There should be a delay between the arrival of the two beams, causing an interference pattern:
10 min

4. There was NO delay, no matter which way the apparatus pointed!
Results:
There was NO delay, no matter which way the apparatus pointed!
Implication:
There is no aether! This baffled scientists until…
5 min

5. Brain break!

6. Einstein’s Theory of Special Relativity Albert Einstein, 1905
The speed of light is the same for all observers (regardless of their state of relative motion)!
5 min

7. Inertial Frame of Reference
The position from which an observer views a particular event.
For example, let’s say Balance is out for a horseback ride…
10 min

8. Postulates of Special Relativity
There is no absolute frame of reference.
The laws of physics are the same in ALL inertial reference frames.
There is NO DIFFERENCE between being AT REST and moving at a constant speed.
The speed of light is the same for all observers (regardless of their state of relative motion).
15 min

9. Unit 9, Lesson 2: Simultaneity and Time Dilation

10. Quick Recap:
10 min

11. Implications of Special Relativity: 1) Simultaneity
Events that are simultaneous in one frame of reference are NOT simultaneous in another!
Example: Train and Lightning Thought Experiment
Two observers: one on a speeding train, one on land.
Observer on land sees lightning strike the front and rear of the train simultaneously.
Observer on the train sees the front of the train struck first, then the rear.
Since the speed of light is the same for all observers, both observers are correct! Simultaneity is relative!
20 min

12. Brain break!

13. Implications of Special Relativity: 2) Time Dilation – “moving clocks run slow”
Example: Light Clock Thought Experiment
20 min

14. Unit 9: Special Relativity Lesson 3: The Twin Paradox

15. The Twin Paradox
There are two identical twins, John and Frank. John goes on a space voyage at nearly the speed of light. Frank remains on Earth. Think-Pair-Share: Who is the younger one when they are reunited? Answer: John. Each one could be perceived to be accelerating from the other’s frame of reference. However, since John is accelerating and decelerating, he cannot correctly make observations, so Frank’s observations are accurate and John comes back younger.
25 min

16. Brain break!

17. Time Dilation Equation
t0 = time experienced by speeding object
t = time experienced by fixed observer
Example: If one year passes on a spaceship going 0.99c, how much time passes on Earth?
25 min
Practice:
Pg. 268 #1-4
t = 7.1 years

18. Unit 9, Lesson 4: Length Contraction and Mass Increase

19. Implications of Special Relativity: 3) Length Contraction
The length of an object is measured to be shorter when it is moving faster.
10 min
l = length of speeding object as measured by fixed observer
l0 = rest-length of object (length when it is at rest relative to observer)

20. Example #1
The Enterprise passes space station “Deep Space 9”. Captain Picard measures the length of the space station to be 600 m, and his own ship to be 200 m. The speed of the ship is 80% of c, relative to DS9.
a) What is the rest-length of DS9?
b) What is the length of Enterprise as measured by someone on DS9? a)
15 min b)
600

21. Example #2 – Try It!
A small space shuttle flies right over Texas at 60% of the speed of light. The pilot looks out the window at a large clock and notes that 15 seconds pass in Texas and the clock is 35 m long. a) How much time ticks by on the space shuttle, according to the pilot? b) How long is the clock according to a Texan?
15 min
12 s
43.75 m

22. Brain break!

23. Implications of Special Relativity: 4) Mass Increase
m = mass of speeding object
m0 = mass of object at rest
Example: How fast would something have to go to double its mass?
15 min
87% of c or 2.6x108 m/s

24. Mass Increase – Why Nothing Can Go Faster Than Light
As the speed of an object approaches c, its mass approaches infinity! Since it is impossible to have greater than infinite mass, then it must also be impossible to exceed the speed of light.
5 min

25. Unit 9, Lesson 5: Mass-Energy Equivalence

26. Implications of Special Relativity: 5) Mass-Energy Equivalence
Mass can be changed into energy, and energy can be changed into mass, according to the equation E = mc2!
This has been experimentally verified. For example, mass is changed into energy in atomic bombs.
Example: How much energy would be produced if 1 kg of mass were completely changed into energy?
E = mc2 = (1.0 kg)(3.0x108 m/s)2 = 9.0x1016 kgm2/s2 or J
This is approximately seven times the total energy of all explosives used in World War Two (including the Hiroshima and Nagasaki bombs).
20 min

27. Brain break!

28. Unit 9 Review Questions
Pg. 274 #2-10
35 min