## 20191104

### Online reading assignment: simple harmonic motion

Physics 205A, fall semester 2019
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.
"Simple harmonic motion is repeated motion back and forth, assuming no outside forces interact with the object, and that under ideal circumstances the motion repeats continuously. When graphed, Simple harmonic motion tends to be similar to a sine/cosine function."

"That the period T is the time it takes for an object in simple harmonic motion to complete one cycle. I also understand that the frequency is related to the period in that the frequency is the number of cycles of the motion per second and can used to find the hertz, or one cycle per second."

"That total energy conservation equals a constant because as KE translational increases then PE elastic will decrease. I also know simple pendulum period is determined by the length of the string which is why in the billiard ball example they all start to swing at different rates even though they are released at the same time."

"That springs have no kinetic energy and maximum potential energy at compression and fully stretched, while they have maximum kinetic energy and no potential energy at equilibrium."

"I don't think I understand anything in this section. I've re-read the section multiple times."

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.
"The part that confuses me is putting it all together. But lecture will help with that."

"I didn't really understand the pendulum period/length stuff."

"I did not really understand the units of certain variables in some of the new functions like L."

"Do pendulum/mass-spring periods always use 2π in the equation?"

"The mass spring period is a little confusing, I feel as though I understand the basis of it. Essentially more mass means more time or T in the mass spring period. Also a weaker spring constant would mean T would be greater. I think."

"There weren't any major things I found confusing. However, it is helpful when we go over the math of the problems and how to sub things in."

"I just need this taught to me. I don't learn well from reading."

"I first was confused on when to use the mass-spring period equation and the energy conservation equation. But then I realized that the first is used when given time and the other when focusing on energy."

"The math in how to perform these examples and the wording in the book is very confusing."

"I understand the basics but I guess the only thing I find 'confusing' is how many formulas are introduced in this chapter. I feel like normally we focus on one or two. I hope you will clarify which ones we will be using primarily."

The total energy of a mass-spring system would have zero translational kinetic energy and all elastic potential energy at the:
 origin (x = 0). ******* [7] turnaround points (x = ±A). ************************************* [37] (Both of the above choices.) * [1] (Neither of the above choices.) [0] (Unsure/lost/guessing/help!) [0]

The total energy of a mass-spring system would have all translational kinetic energy and zero elastic potential energy at the:
 origin (x = 0). ************************************* [37] turnaround points (x = ±A). ****** [6] (Both of the above choices.) [0] (Neither of the above choices.) ** [2] (Unsure/lost/guessing/help!) [0]

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. ***************************************** [41] equal to. ** [2] longer than. [0] (Unsure/lost/guessing/help!) ** [2]

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. ***** [5] equal to. ************** [14] longer than. ************************** [26] (Unsure/lost/guessing/help!) [0]

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. ************************* [25] have no affect on. * [1] increase. *************** [15] (Unsure/lost/guessing/help!) **** [4]

For this mass connected to two springs, its springs weakening over time (decreasing its spring constant) would __________ the period of oscillation.
 decrease. ********************** [22] have no affect on. **** [4] increase. *************** [15] (Unsure/lost/guessing/help!) **** [4]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Go over these."

"I didn't understand the swing question, they have different masses but appear to be swinging the same." (Yes, that is exactly what you should be seeing.)

"How much more will we be working with springs and stuff?" (You'll have a lab on this later, where you tinker around with periods of pendulum and mass-spring systems.)

"Seems simple enough."

"I'm never going to understand physics."

"Life is really getting to me now."

"I can't believe it's already November :|"