Resonance and standing waves were once again on the docket. And today we added the sounds produced by stringed instruments. Using the free computer program "Audacity" we were able to record and analyze the sound produced by a violin, a ukelele, a guitar, and that glass that we made "ring." Even playing the same note, these instruments sound different from each other. Today we could see why: Although they produced the same fundamental frequency, the also produced 2nd, 3rd, 4th and higher harmonics, but at different loudnesses. It is the mix of all those frequencies, each at its particular loudness, that produces the full sound that we hear. Because the mix of frequencies and the particular loudness of each frequency differ, the total sound that we hear differs.
The pictures above are from two violins sounding the note G, and even they are not identical when playing the same note. But they are very similar. Remember, the y-value on the plots represents the loudness of a frequency, while the frequency is the x-value. We also saw a short documentary about the Tacoma Narrows Bridge Collapse. Pretty amazing to see steel and concrete bend so much! Assignment:
We discussed and observed more wave behavior today. We now should understand what is meant by
Assignment: Ch 11 P: 36, 37, 52, 55, 56, 57 We took a quick quiz as a "check up" today. It was about energy in a pendulum system. We check out our Periodic Wave Properties homework, and turned them in. Then we turned our attention to the behavior of waves when they meet (superposition) and when they reflect from fixed points and from free ends of a medium. We also considered what happens when waves from two different sources meet. In that case we saw an interference pattern develop, a pattern in which there are "nodes," which are places where waves from the two sources meet but add up to zero displacement. Here's a link to that simulation: http://www.falstad.com/ripple/
We also used the simulation linked above to observe refraction, which is the change in direction experienced by a wave as it changes speed when traveling from one medium to another. Assignment: Periodic Wave Graphs What can you learn about the waves represented in the two plots shown above? Which is a snapshot plot, and which is a history plot? You should be able to figure out what you can about the waves represented in each of these plots, and the kind of information is slightly different.
Why does the mathematical relationship above make sense? You should be able to describe its meaning to someone else. Assignment:
We presented our solutions to Ch 11 P: 28, 29, 30, and 82 today. Then we turned them in. It seemed to go well.
Next we began our investigation of waves, which will be of use to us when we study sound and later in the year when we study light, too. Beyond that, it turns out that we need to use wave functions to describe electrons in atoms, so waves have something to do with what we think of as particles, things like electrons and protons. The upshot is that waves are powerful models that can be used to account for all kinds of things. We begin our study of waves now. Assignment: Plan for the rest of the week:
We finished up our foray into energy and forces in a pendulum system today and turned in our homework assignment. Next up was the Safety Quiz followed by a reminder of what "period" and "frequency" are. On Monday we will begin our study of waves.
Assignment:
Our focus today was how to figure out the forces acting on a pendulum bob. Simple system, but subtle ideas about what we mean by "forces." So we had an interesting (to me, anyway!) discussion about these forces. And, in a way, it was a review of much of Physics I. We will wrap up our work on that worksheet tomorrow, and we will start our study of waves, something that will occupy us for a few weeks.
Assignment
Aside from the routine information about the course, we engaged physics where Physics I left off last year, namely, with pendulums. Specifically, we began to work with kinetic energy and potential energy in a pendulum system.
Assignment:
And regarding Perseus, here's the lowdown on the namesake of the Perseid Meteor Shower: https://www.laphamsquarterly.org/luck/gorgons-head Our first weekend of the new school year will be highlighted by the Perseid meteor shower. If you take the time, and the sky is clear, over the weekend you should be able to see several meteors while watching the sky at night over a half hour or so. The meteors are dust and pebbles that have come off of Comet Swift-Tuttle over the years, and they hit Earth's atmosphere at a speed of about 30 miles per second. That's enough energy to knock off electrons from air molecules. When electrons recombine with these ions they "fall" through the different orbitals with their associated energy levels. And just as with the Bohr model of the hydrogen atom, light is emitted. The light from all those recombinations along the pebble's path is what we see as a streak in the sky.
Really good information about watching for Perseids can be found here. And what's the deal with Perseus? Is he all that? And what's up with the Demon Star in Perseus, Algol? Gorgon...really?? Tomorrow is the day! See you then. |
Physics IIMr. Swackhamer Archives
May 2019
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