## 20151109

### Online reading assignment: simple harmonic motion

Physics 205A, fall semester 2015
Cuesta College, San Luis Obispo, CA

Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing a presentation on simple harmonic motion.

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"The mass-spring period is expressed as T = 2π√(m/k) while the simple pendulum period is expressed as T = 2π√(L/g). The numerator in both expressions is the inertial parameter, and the denominator is the restoring parameter. Increases of pendulum length or mass increases the period, while increases in the gravitational constant or spring strength decreases the period."

"I understand how E = KEtr + KEelas."

"The 'simple' in 'simple harmonic motion' means that we will ignore any outside work being done by external sources and dissipation forces such that under this ideal condition the back-and-forth motion of the object will continue forever."

"Springs contain elastic potential energy."

"I understand that when the simple pendulum length increases, the time to complete a cycle of motion increases. This applies to mass-spring system also, if the mass increases so does the time to complete one cycle."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"How the sums of KEtr and KEelas always equal a constant amount in total energy conservation."

"I don't fully understand the significance of an 'inertial parameter' and a 'restoring parameter.'"

"I think I generally understand the basics. I'm confused when it comes to applying my basic understanding of the topic matter."

"A little confused about the periods. When do you use mass and when do you use length in the equations?"

"I do not understand how to apply these concepts. All I got was the formulas, not what they actually mean."

"Nothing much, maybe just some more review and problems."

The total energy of a mass-spring system would have zero translational kinetic energy and all elastic potential energy at the:
 origin (x = 0). ********* [9] turnaround points (x = ±A). **************************************** [40] (Both of the above choices.) ******* [7] (Neither of the above choices.) * [1] (Unsure/lost/guessing/help!) ***** [5]

The total energy of a mass-spring system would have all translational kinetic energy and zero elastic potential energy at the:
 origin (x = 0). ******************************** [32] turnaround points (x = ±A). [14] (Both of the above choices.) **** [4] (Neither of the above choices.) ****** [6] (Unsure/lost/guessing/help!) ***** [5]

For these identical mass billiard balls hanging from strings of different lengths, the billiard balls hanging from shorter length strings have periods that are _________ the periods of the billiard balls hanging from longer length strings.
 shorter than. ************************************************ [48] equal to. ******* [7] longer than. ** [2] (Unsure/lost/guessing/help!) **** [4]

For the different mass riders on swings of the same lengths, the more massive rider has a period __________ the period of the less massive rider.
 shorter than. **** [4] equal to. ***************** [17] longer than. ************************************ [36] (Unsure/lost/guessing/help!) **** [4]

For the overloaded truck with a vertical oscillation period of approximately half a second, after dumping its load (thus decreasing the mass connected to the springs in its suspension) would __________ the period of oscillation.
 decrease. ************************************* [37] have no affect on. ** [2] increase. ************ [12] (Unsure/lost/guessing/help!) ********** [10]

For this mass connected to two springs, its springs weakening over time (decreasing its spring constant) would __________ the period of oscillation.
 decrease. ******************** [20] have no affect on. **** [4] increase. ***************************** [29] (Unsure/lost/guessing/help!) ******** [8]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
""I simply cannot escape Miley Cyrus--even my physics instructor brings her up." (All you ever did was break me.)

"Just could use in-class discussion of everything."

"That was easy."

"I am behind."

"Does the 'pulling' force of a stretched spring constitute elastic potential energy? In other words, for the mass on spring animation, is there always elastic potential energy (as long as the mass is oscillating)?" (Well, there is always elastic potential energy in the spring as long as the spring is stretched or scrunched. If the spring is momentarily relaxed at its equilibrium position (but the mass is still in i), then all of the elastic potential energy is in the form of the mass' translational kinetic energy.)

"If I had to tell you how to find total energy conservation, I would quit and tell you to just forget about it. Bad opinion?"

"Dr. P-dog, what is a 'physic?'" (Apparently it's something that's supposed to be good for you.)

"I'm going to a classical music concert this evening. I enjoy classical music a lot, but I'm pretty sure I just paid \$20 to take a two-hour nap." (Players gonna play, nappers gonna nap. #donthatetheplayerhatethegame #theyseemenappingtheybehating)