Cuesta College, San Luis Obispo, CA
Students have a 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 something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"For some reason it finally clicked in me that all forms of energy can be expressed in joules. i'm not sure why this is just now making sense to me, but it was interesting."
"It was really cool to see how [rotational kinetic energy] fits neatly into the energy transfer/balance equation. I love how interconnected physics can be."
"That the shape of an object and where the axis of rotation lies, is significant to determine the rotational inertia."
"That rolling objects have both translational kinetic energy and rotational kinetic energy. It makes sense to me. Side note: the animated *.gif for the moving company example was pretty amusing!"
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Perhaps it was because I read the online assignment in the morning without any coffee in my system, but I had to re-read the assignment a couple of times more than usual to understand it. It felt a little bit overly complex because the ideas at the core of the section are somewhat simple. Then again, I suppose that's just physics."
"I found the section on rotational kinetic energy and rotational inertia to be a little confusing and could benefit from some in class discussion or more explanation of the formulas and how to apply them."
What is the SI unit for rotational kinetic energy?
"N·m, or J."
"Joules."
"Torque."
"kg·m2."
"Krot = (1/2)·I·ω2."
"kg·m2·rad2/s2."
Briefly describe an example of an object that has both translational kinetic energy and rotational kinetic energy.
"A ball rolling down a hill."
"A Frisbee® thrown forward and spinning."
"A bowling ball. It rolls towards the pins, but is also moving in a specific direction with specific speed."
"A golf ball as it has been hit. It spins and it travels."
"Earth--it has motion through space and rotates about its the axis."
Briefly describe an example of an object that only has rotational kinetic energy, and no translational kinetic energy.
"A merry-go-round."
"A vinyl record that is playing on a turntable."
"A ceiling fan."
When a lever arm (or moment arm) is drawn, briefly explain where it starts, and where it ends.
"The lever arm starts from the rotation axis and ends at the line of action."
"It starts at one end at the pivot point, and intersects the line of action at a perpendicular angle."
For the large spool of cable rolling without slipping down the staircase (*.gif), mark whether the changes in energy are increasing (+), decreasing (-), or remain constant (0). (Assume no energy lost to non-conservative work: Wnc = 0.)
(Only correct responses shown.)
Change in translational kinetic energy ∆Ktrans : increases [77%]
Change in rotational kinetic energy ∆Krot : increases [77%]
Change in gravitational kinetic energy ∆Ugrav : decreases [71%]
Change in elastic potential energy ∆Uelas : remains constant [71%]
"Kill me now. (No. Not yet. But soon.)
"Is rotational inertia simply a part of the rotational kinetic energy equation?" (Yes. A really important part.)
"Could you explain a little more the difference between translational and rotational kinetic energy?" (We'll do examples with both types of kinetic energy.)
"Do we often neglect friction and drag to make things more simple to learn or because it is similar to an outer space environment? Both? Neither?" (Both. If you are faced with more realistic situations where friction and drag can't be ignored...then you're an engineer.)
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