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 rotational dynamics.
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.
"Rotational inertia depends on mass and radius, while the rotational kinetic energy depends on rotational inertia and angular speed (squared)."
"An object with both translational motion and rotational motion also has translational kinetic energy and rotational kinetic energy."
"It is cool to think about how similar the translational speed and the angular speed of a rolling object are related, and the relationship between mass and the rotational inertia of the object."
"An object doesn't have to possess both translational and rotational kinetic energies at the same time. Rotational kinetic energy is the energy of a rotational motion about an axis, and it depends on the rotational inertia of the object. Translational kinetic energy depends on motion through space. There are formulas to calculate these kinetic energies, but that part I am currently struggling with.
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 understand the concept of rotational inertial, moment of inertia, and rotational kinetic energy. However, when it comes down to applying it to the given problems it gets somewhat confusing."
"I found some of the symbols to be confusing. I will get used to the symbols though."
"The difference between rotational kinetic energy and translational kinetic energy really confuses me."
"Nothing quite yet. Usually my questions come with clarifications while in class, when we get more of an exposed understanding."
"I find the formulas/equations for this assignment extremely confusing to follow along with. Hopefully with some in class examples and practice I will be able to use them correctly."
What is the SI (Système International) unit for rotational kinetic energy?
"Joules."
"kg·m2/s2."
"rev/s or rad/s."
"rad/s2."
Describe an object that only has rotational kinetic energy, and no translational kinetic energy.
"Hamster wheel."
"Windmill."
"Stationary bike."
"A record turntable."
"Any object on a fixed axis."
"I am not sure."
Describe an object that has both translational kinetic energy and rotational kinetic energy.
"A ball rolling down the street."
"A tire rolling down a hill."
"Driving a car--it has both transnational kinetic energy and rotational kinetic energy, because the wheels must rotate to move the car and which also must translate."
"I'm not sure how to describe an example."
(Only correct responses shown.)
Gravitational potential energy: decreases [69%]
Translational kinetic energy: increases [75%]
Rotational kinetic energy: increases [78%]
From starting at the top of the ramp to the bottom of the ramp, the energy form that experienced the greatest amount of change (increase or decrease) was the tire's:
gravitational potential energy. ************* [13] translational kinetic energy. ***** [5] rotational kinetic energy. ************ [12] (There is a tie.) ******************* [19] (Unsure/lost/guessing/help!) ********** [10]
(Only correct responses shown.)
Gravitational potential energy: increases [63%]
Translational kinetic energy: decreases [48%]
Rotational kinetic energy: no change [39%]
For the subsequent part of this stunt, from just as it leaves the second ramp to reaching the top of its trajectory, the energy form that experienced the greatest amount of change (increase or decrease) was the tire's:
gravitational potential energy. ******************** [20] translational kinetic energy. ******* [7] rotational kinetic energy. ******* [7] (There is a tie.) ************ [12] (Unsure/lost/guessing/help!) ************* [13]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I would like to know how the rotational inertia factors are what they are. How are they derived?" (Integral calculus. You don't want to go there.)
"Will we have to memorize all of these equations or will they be given to us?" (You will be given all the equations you need for the quizzes and exams. And rotational inertia for any relevant object.)
"The textbook sections were so hard to read. The blog simplified it but being taught what equations to use and how to decipher problems would be helpful."
"I enjoyed reading about this section."
"Why is m·r2 called the 'moment of inertia?'" (Because, integral calculus. Actually m·r2 is the rotational inertia of a single point mass, if you have a distribution of point masses that make up an extended object, then to find the rotational inertia of that object you would need to add up all of its individual point-mass rotational inertiae--that is, integrate m·r2 over the entire object. #notgoingthere)
"What is your ideal temperature? Mine is 66°F." (Cool. Cool cool cool.)
"I secretly want to become a mechanic, because I'm in love with cars but I'm also working towards becoming a physician's assistant. So why not do both? #hatersgonnahatesomemore" (#learnallthethings)
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