POST AP 02: SR Vis

I hope you enjoyed your very first Rock Opera... for some folks it can be something of an (how shall I say....)

Acquired Taste?

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As is sometimes the case, I had a bit of an ulterior motive in having you folks do that, what might that have been? <please discuss>

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So... along those lines, I have a VERY cool activity for you today, but it's gonna start out a little *ahem* different. Please roll with it.

To wit:

Let's arrange seats back to back in a circle

After each prompt you'll move from inner to outer.

The outer person ALWAYS talks, the inner person ALWAYS listens. The inner person (so to speak) can ask very brief (less than 10 words please) clarifying questions only.

If we have an odd number of students today, we'll swap out a person each round to be the prompter. If we have an even number, I'll do the prompting.

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Prompt
Time
Imagine you are on a sidewalk cafe in a town square in some European capital. Describe that scene to your partner.
2:00
Imagine you are in a turn-of-the-19th century office in that same capital, with a view of that same town square. Describe that to your partner.
2:00
Imagine you are a mid-level civil servant in your own turn-of-the-19th century office in that same capital, with a view of that same town square. Describe your office to your partner now please.
2:00
Imagine you are a patent clerk in that office. Your job is to use your physics, math and engineering skills to approve or deny inventions that come to you for patent review. Describe an average work day to your partner.
2:00

It turns out you are a Swiss Patent Clerk, the city is Geneva, and the year is 1905. You finish your days with much time to spare and you start thinking very cosmological thoughts involving the "ether".

At that time, scientists thought the universe was full of some sort of substance that allowed light to propagate. The more you think about it, the less you believe there *is* an ether at all. Talk about that.

2:00
Now that you've dispensed with the ether and the more you work with Maxwell's E & M Equations, the more you come to believe that the speed of light is constant among all frames of references at all times. What comes to mind?
1:30
You start working on a "Thought Experiment" to evaluate a constant speed of light. Since you see the train station every day, your thoughts naturally turn to a train. You imagine an observer watching a train go by compared to a passenger on the train. What might you consider?
2:00

You refine your thought experiment so that your observer is watching the train go by at NEAR the speed of light.

The passenger watches a single photon move from a flashlight to the ceiling... what does the observer see?

2:00
Let's return to your regularly scheduled seats

Using simple images from his day-to-day life and nothing more than basic high school algebra, Einstein was able to formulate a powerful relationship between time and the speed of light (c).

Let's recap:

A passenger onboard a train watches a single photon move from a flashlight to the ceiling.

An observer outside watches the train go by at .90 c

The observer also watches the photon move from the flashlight to the ceiling of the train compartment where the passenger is seated.

Work with your group to see if you discern the radical departure that Einstein embarked upon in this thought experiment.

 

 

 

Answer: This thought experiment offers the very radical suggestion that the speed of light is constant in both reference frames.

  • Have a conversation and see if you can suggest how keeping c constant in BOTH reference frames would impact displacement calculations in each reference frame?

Let's start with the passenger watching the photon inside the cabin.

  • What does the passenger see the photon do (draw and label a sketch)?
  • Using the most simple rate equation, how would the passenger calculate the displacement for that photon moving from a flashlight to the roof of the cabin?

Now let's switch to the observer in a different frame of reference (watching the train go by from outside the train) and let's say the train is moving at .90 c:

  • What does the observer see the photon do (draw and label a sketch)?
  • Using the most simple rate equation, how would the observer calculate the displacement for that photon moving from a flashlight to the roof of the cabin?
  • How does that observer calculate the displacement of that train during that same?

Here is another amazing insight that Einstein obtained: He related all three of those displacements to determine a relationship between time inside, time outside and the speed of the train:

 

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