Monday, July 21, 2014

Circuits and Lasers and Viscous Fluids, Oh My!

Today, the first thing we did in physics was rank our choices for our interest groups (the Franck-Hertz experiment, High-Energy Physics, Quantum Mechanics, Radio Telescopes, Non-Newtonian Fluids, or Behavior of Charged Particles) and hand the slips back to Craig, who promised he would tell us what groups we were in before lunch. This was a necessity because we were going to be starting our projects in those groups immediately after lunch. Luckily, I got in to my first choice--quantum mechanics.

Bill explains the experiment we will be doing to measure the speed of light.
Then Bill talked about how all the greatest physicists, for example Newton, Einstein, and Feynman, had been rebels (not to encourage us to act out, or anything). He also told us the history of our morning lab (finding the speed of light), which went all the way back to Galileo, who first theorized that the speed of light was not infinite. He even did experiments to try to determine the speed of light. Unfortunately, his conclusion was that the speed of light was either infinite or too fast to be measured with the current technology. Then Roemer calculated the speed of light using the movement of Earth and Jupiter's moons, because the distances were so great that the time differences could be easily measured. However, the astronomers of his day did not know the radius of the Earth's orbit, so the number he calculated for the speed of light was wrong, though his math was correct. Now, we can make such precise measurements with state-of-the-art equipment that measuring the speed of light is trivial. (Since we don't have access to state-of-the-art equipment, and we're pretending we don't have access to Google either, we're measuring the speed of light with long hallways and moderately advanced technology. In the lab today, we put together all of our own circuits and other equipment for the setup we need to measure the speed of light--the actual experiment will be continued tomorrow.)

Our equipment was much less assembled than we had expected.
Then our guest lecturer, Phil Nelson, came for a second time, this time to talk to us about fluid mechanics. First he showed us that when you mix something slowly in corn syrup, you can "unmix" it. This is a property of viscous fluids. We also derived a formula for viscosity based on area, velocity, and density, which showed that very small creatures--like bacteria--experience water as much more viscous than we do. That's why they have to swim with whip-like or corkscrewing flagella, because a back-and-forth motion gets them nowhere.

After lunch, we split up into our interest groups. Because the Franck-Hertz experiment and Quantum Mechanics are closely linked--and because Bill is the expert for both of them--they were in the same room. For Quantum Mechanics, we are doing the double-slit experiment with single photons to show that even when you force light to be a particle--by only letting it out one photon at a time--it still acts like a wave and interferes with itself. You cannot determine a photon's position, it's all statistical. As Bill said, "It's like trying to find light bulbs by firing bullets at them." Today, we mostly just took measurements. We will continue the experiment tomorrow and the next day.

Interestingly, all of the clocks in the physics department appear to have experienced time at relativistic speeds.

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