Online reading assignment: simple harmonic motion

Physics 205A, fall semester 2017
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 when the outside work on the object is being ignored, and under this ideal condition the back and forth motion of the object will continue forever."

"I felt like I got a solid grasp of the total energy conservation problems after reading the assigned material and looking over the blog."

"The further an object is from the origin the higher the elastic potential energy and vice versa for the kinetic energy."

"From the presentation, I understand the concept of total energy conservation. This models the previous conservation equations we've covered, and so it makes sense that energy must be conserved and one value must always consistently equal the other side of the equation. I understand how a spring can have kinetic energy (depending from where you start measuring it), as well as potential energy."

"An ideal spring is F_spring = –k·x and has no weight. Frequency is the number of cycles per second."

"In harmonic motion (uniform, symmetric oscillations) energy is transferred between KEtr and PEelas in a period matching the symmetric oscillation. Pendulums with a mass at one end vary in period depending on length of string. For a spring loaded with a mass, the mass determines period. However, the spring constant can weaken over time."

"The thing that I found most interesting and the thing that I understand the best from the assigned reading assignment was the pendulum part."

"A mass on a spring undergoing simple harmonic motion will have a constant total mechanical energy E. For a simple pendulum, the period depends on the square root of the string length L and the gravitational acceleration g."

"This section feels more challenging. I understand that as mass of a load increases, time for a spring or swing to go through a complete cycle is greater. I understand the components of the equations and the application of the equations."

"Honestly, I didn't get to this (yet)."

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 need the simple pendulum period explained, I can't understand how the book explains it."

"I'm not completely getting the mass on the spring and when it talks about translational kinetic energy and elastic potential energy. When one is zero, where is the other energy?"

"I am struggling with the total energy conservation equation."

"I think I need more clarification on energy conservation through the mass-spring concept."

"For now, everything else is confusing. I have a hard time comparing something increasing and decreasing. However when it remains constant, it is easier to make sense of the situation."

"I found the pendulum confusing. I don't really understand how its period work."

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

origin (x = 0).	***** [5]
turnaround points (x = ±A).	********************************* [33]
(Both of the above choices.)	***** [5]
(Neither of the above choices.)	* [1]
(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).	**************************** [28]
turnaround points (x = ±A).	********* [9]
(Both of the above choices.)	**** [4]
(Neither of the above choices.)	** [2]
(Unsure/lost/guessing/help!)	* [1]

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.	************************************* [37]
equal to.	****** [6]
longer than.	[0]
(Unsure/lost/guessing/help!)	* [1]

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.	******** [8]
equal to.	************ [12]
longer than.	************************ [24]
(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.	************************ [24]
have no affect on.	**** [4]
increase.	************* [13]
(Unsure/lost/guessing/help!)	*** [3]

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

decrease.	************* [13]
have no affect on.	**** [4]
increase.	************************** [26]
(Unsure/lost/guessing/help!)	* [1]

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

"I don't really understand simple harmonic motion and amplitude. A is amplitude, correct?" (Yes.)

"I think I understand this section. The reading was a little tough but your blog helped me understand it better."

"I have learned that I’m more of a visual learner so I could use a visual on how the formulas work. I get that the sum of the two energies has to equal the total mechanical energy, but just some overview would be great."

"Brief review on different mass pendulum problems would be great. When mass increases on a pendulum, would the period increase?" (No.)

"Very unsure about the weakening spring example above, but my inclination tells me the oscillation period would decrease."

"What is the spring constant k?" (It's a measure of how "strong" a spring is, in N/m. So a very weak spring might need only 0.001 N to stretch it by 1 m, while a very strong spring would need 1,000 N to stretch it by 1 m.")

"I could use more examples just to clarify. I think once we practice it in class, I will more clearly understand."

"I don't get what happens as the springs weaken over time."

"Please go over the questions from the second half of the presentation!"

"I'm a little confused by the decreasing the mass of an overload truck equation. it seems that it doesn't directly apply to either equation because it is a different kind of motion."

"Mostly how to do problems of frequency. Are we always expected to assume a spring is ideal?" (You should always be told whether a spring is ideal (or not).)

"I am still very much enjoying your class!"