In second semester physics, we spent first two weeks on oscillations.
Day 1: Linear Restoring Forces
We first explored and played with variety of springs and talked about what we noticed. Students noticed varying lengths, coil thicknesses, and diameters. They noticed different materials, that some only stretch, while others stretch and compress, that they have different stiffnesses, that some have “hoops” or “hooks” at their end.
We also talked about what other things in this world are described as “springy” but not really springs. Diving boards, skin, trampolines, exercise bands, bouncy balls, etc. I reminded students that last semester we saw that lots of surfaces are springy, but often very stiff (normal forces).
Next students were asked to qualitatively rank the springs in terms of stiffness. We talked about what factors seem to make certain springs stiff or loose. I Guided / helped Create a need to quantify, which led into invention tasks for spring stiffness. Ended the day using force sensors to measure spring constants and compare to our ordering. We needed more practice reasoning about …
Day 2: Describing Oscillations / SHM
Started with a mix of prediction and observation tasks with motion detectors of a vertical oscillator. Lots of position, velocity, and acceleration. I have a diverse group in terms of familiarly with kinemarics graphs, and facility distinguishing velocity and acceleration. Next time I would start with more review of free fall and looking at graphs, or see my note below about bungees.
Some direct instruction and practice with sinusoidal functions, as well as amplitude, period, frequency, including clicker questions and ranking tasks. That amplitude doesn’t effect period is a culminating finding. This day ended with problems that helped students connect graphs to equations and physical meaning.
Next year we definitely need to have students play around with feeling of being yanked back and forth by a bungee, before jumping into graphs.
Day 3: Factors that affect frequency
We explored meter sticks wobbling, and how stiffness and mass effect frequency. Students are asked to make claims and support with evidence, but also to try to connect to everyday experience… a lot of this is fun, students connect to music, other students connect to Newtons 2nd law. We had fun making slow motion vids.
We go back to springs and I model how to use logger Pro to get period/frequency two ways… Data marking and curve fitting. We all do same data point, 200 g on a 15 N/m spring. We plot that point on graph at front o Room and then students are tasked with getting data for other masses. Before collecting students must predict where their next point might be and to support claim by referencing what we leaned earlier in the day.
We build our data and model together and then I did some brief direct instruction, which was followed by clicker questions, ranking tasks, and one brief numerical exercise.
Day 4: Energy in SHM
We did some review about what we’ve learned about SHM, so far. Worked the beginning of a problem we would later tackle with energy. Students were given mass, spring constant, and amplitude, and asked to graph position vs time and force va time, with extrema and period labeled quantitatively.
We then did some “review” of energy. This led us into working a 1st semester problem of child going down a slide. Students then observed pendulum swing and phet energy skate park– how similar and different than the child on slide? We then looked at oscillators driven by elastic potential energy, rather than gravitational and did clicker questions pertaining to where maximum / min KE and PE occur. And also some questions about how we can get more total energy in a system.
Students went back to problem of the beginning of day to tackle from an energy perspective… finding total energy, maximum speed, and speed and half amplitude. Students were asked to add velocity vs time graph and an energy vs time graph.
Day 5: intro to waves
Next week we get out microphones and start exploring the oscillating behavior of that data. We’ll start really just playing around,trying to make sounds that do and don’t look like the graphs we’ve seen from SHM. Once we can get some graphs that look good, we use methods from previous week to explore frequency and period. Probably get some tuning forks out, and maybe even try and record our wobbly metersticks experiments.
Students then get two microphones and a low frequency sound to compare output when microphones are placed in different locations. How does amplitude compare? How does the frequency compare? … some guidance gets students considering “phase”
This leads into an introduction to waves as oscillatory energy on the move, and a pivot away from sound and toward waves on slinkies.
Students play with slinkies, with some guiding questions to get them to explore how to make tall vs short pulses, and how to make fat vs thin pulses. Some questions get us observing wave speed down the slinky vs transverse motion of coils.
This then transitions to looking at phet sim with waves on string.
To get us back to the textbook, I introduce and we practice picture graphs (displacment vs position at a particular moment) for history graphs (displacement vs time for a particular location). We’ll do some clicker questions and other various practice with making and interpreting those graphs.
At some point next week we’ll need to wade into factors that effect wave speed, sinusoidal waves, etc.
Leave a Reply