Online reading assignment: simple harmonic motion

Physics 205A, fall semester 2018
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.

"A period is the time for the mass to complete one cycle of motion."

"Simple harmonic motion is back-and-forth motion. I found it interesting that we can relate its motion to sine and cosine graphs and how the two are related."

"The simplest form of periodic motion is simple harmonic motion. The spring constant is labeled k in the equation, and the stiffer the spring, the greater the value for k. Force is not constant so velocity and acceleration are not constant and constant acceleration kinematic equations do not apply."

"Simple harmonic motion is a special type of periodic motion or oscillation motion where the restoring force is directly proportional to the displacement and acts in the direction opposite to that of displacement. For a simple pendulum, the period depends on the square root of the string length L and the gravitational acceleration g."

"Simple harmonic motion refers to the constant back-and-forth motion of an object (ignoring any outside external forces of course), where a position versus time graph will produce either a cosine or sine function. We can analyze this motion with energy conservation equations."

"For a greater mass, the period of a mass-spring system increases. Also, the harmonic motion can be illustrated with sine/cosine graphs."

"Shorter strings on a pendulum would have shorter periods."

"When talking about the conservation of energy it's important to understand that energy is always conserved, it never just disappears it always turns into a different form on energy, when looking at say a spring problem it's important to look at the position of the spring to determine what type of energy it has. For a pendulum the mass doesn't affect its period, rather it's all about the length of the string. For the period of oscillation the bigger the spring constant the smaller the period and the vice versa."

"In the energy conservation equation, the total of both translational energy and elastic potential energy must equal to a constant, because no energy is lost or gained from the outside world/surroundings."

"That in harmonic motion external forces are ignored, which means the system will never come to a stop (total mechanical motion will be constant)."

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.

"I was confused about what moment an object would have no translational KE or no elastic PE. Changing spring strength was a little confusing on how it would effect the period."

"Going over these chapters I still feel uncomfortable with oscillation and would greatly appreciate more guidance in class."

"How translational kinetic energy changes when the object moves away from and to its equilibrium position."

"Mass has no effect on the period of a pendulum?"

"For the pendulum period, I just thought that maybe a bigger mass would cause it to have a shorter time period because it is more mass pulling it down."

"I don't understand how increasing the gravitational constant would decrease the period of a pendulum."

"Something that confused me at first was the heavier masses for a pendulum period. I thought the mass didn't affect the swing, but after looking closely at the video, it helped me understand it more."
"Trying to find the simple harmonic motion periods with the simple pendulums and mass springs. Mathematically why would the period be the square root of the length over the gravitational acceleration."
"I'm just confused on the spring constant. Is it given? I'm cornfused. Also maybe just confused about the statement 'even though the relative amounts of KE_tr and PE_elas may be different, their total must always equal the same constant amount.' I need a picture I think."

"Nothing was really confusing in the assigned reading, I understood the basics. Maybe just a review of the mass-spring periods."

"I felt like I understood most of the presentation. I don't currently have any questions, but I may after lecture."

The total energy of a mass-spring system would have zero translational kinetic energy and all elastic potential energy at the:

origin (x = 0).	************ [12]
turnaround points (x = ±A).	***************************** [29]
(Both of the above choices.)	* [1]
(Neither of the above choices.)	** [2]
(Unsure/lost/guessing/help!)	****** [6]

The total energy of a mass-spring system would have all translational kinetic energy and zero elastic potential energy at the:

origin (x = 0).	***************************** [29]
turnaround points (x = ±A).	*********** [11]
(Both of the above choices.)	[0]
(Neither of the above choices.)	**** [4]
(Unsure/lost/guessing/help!)	****** [6]

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.	******************************************** [44]
equal to.	** [2]
longer than.	[0]
(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.	****** [6]
equal to.	********* [9]
longer than.	***************************** [29]
(Unsure/lost/guessing/help!)	****** [6]

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.	******************************** [32]
have no affect on.	[0]
increase.	********** [10]
(Unsure/lost/guessing/help!)	******** [8]

For this mass connected to two springs, its springs weakening over time (decreasing its spring constant) would __________ the period of oscillation.

decrease.	********************* [21]
have no affect on.	** [2]
increase.	******************** [20]
(Unsure/lost/guessing/help!)	******* [7]

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

"When you state that 'increasing the gravitational constant (by changing its location?) would decrease the time to complete one cycle of motion,' are you stating that the object is in a different altitude? or different planet with a different constant?" (Yes. In fact, timing a pendulum period at different locations can be used to determine variations in the gravitational constant.)

"I don't fully concentrate on newer material when I need to concentrate on older material. I wish I was able to, but I need to focus on what we are being quizzed on." (I still appreciate the effort in at least skimming the material we'll be introducing for this class after the quiz.)

"I didn't get to the reading tonight because I've been studying for other exams; my bad." (Good luck!)

"Mythbust this: does a golf ball travel farther if the club head is wet?" (Sounds like a great abstract. Send me the rest of this lab report when you find out.)

"This section was very confusing for me!"