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.
"The differences between rotational and translational kinetic energies."
"Rotational inertia depends on the mass and size of an object."
"That rotational parameters and translational parameters are related to each other by the radius of the object that rolls without slipping. I also understood that the higher the rotational speed, the higher the rotational kinetic energy."
"I understand the basic concept of angular speed and how it relates to translational speed. I get that the angular speed can be the same between two rolling objects, but if the radii are different, the objects will travel at different speeds."
"Rotational inertia is a property of an object which can be rotated. There is a relationship between the mass and the rotational inertia of an object. Rotational kinetic energy is the energy of rotational motion."
"Angular velocity describes the motion of a rigid object rotating about a fixed axis. A change in velocity means angular acceleration is occurring. The net external torque is proportional to angular acceleration."
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.
"Rolling without slipping. Rotational kinetic energy term in the transfer/balance equation."
"Angular speed and rotational inertia--I would like to see examples of these problems worked out."
"There were so many equations how do I apply them?"
"Although I read it over and over again, I found it hard understanding what rotational inertia means."
"I found the majority of this section to be very confusing. I still don't really understand how to calculate anything, how angular speed and rotational kinetic energy relate, and pretty much anything related to rotational inertia."
"Applying the transfer/balance equation to situations is kinda difficult to grasp. How can you figure out which energy system experienced a greater change?"
"I think I'm getting what's going on!"
"I understood pretty much everything in this chapter."
What is the SI (Système International) unit for rotational kinetic energy?
"J (joules)."
"Joules (kg·m2/s2)."
"(1/2)·I·ω2."
"I have no idea :( "
"I just didn't get to this (yet)."
Describe an object that only has rotational kinetic energy, and no translational kinetic energy.
"A hamster wheel that spins in place."
"A top that spins."
"A stationary table saw that spins in order to cut wood."
"A wheel of a car getting brake-tested or balanced on a stationary platform."
"Windmill."
"Ice skater spinning."
"A Ferris wheel."
"A ball connected to a string being spun in a circle."
Describe an object that has both translational kinetic energy and rotational kinetic energy.
"A wheel rolling down a hill."
"Tire rolling across the ground."
"A hamster ball."
"A Solowheel has both translational kinetic energy and rotational kinetic energy."
"A hula hoop rolling across the floor without slipping."
"Skateboards."
(Only correct responses shown.)
Gravitational potential energy: decreases [81%]
Translational kinetic energy: increases [85%]
Rotational kinetic energy: increases [77%]
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. *********** [11] translational kinetic energy. ********* [9] rotational kinetic energy. ******* [7] (There is a tie.) *********** [11] (Unsure/lost/guessing/help!) ********* [9]
(Only correct responses shown.)
Gravitational potential energy: increases [87%]
Translational kinetic energy: decreases [61%]
Rotational kinetic energy: no change [40%]
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. ********************* [21] translational kinetic energy. ******* [7] rotational kinetic energy. ***** [5] (There is a tie.) ***** [5] (Unsure/lost/guessing/help!) ********* [9]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I have a question not necessarily on this reading assignment, but rather from the collisions section. Going over the practice quiz one of the options when comparing various different collisions there was an option to pick: 'translational kinetic energy and/or momentum cannot be determined.' I was wondering if there is ever a situation during a collision that conservation for either quantity can't truly be determined?" (Only if the presence (or absence) of external forces during the (brief) collision are unknown. If there are external forces present during the collision, then both quantities can't be conserved. If there are no external forces during the collision, then momentum is conserved, but translational kinetic energy may or may not be conserved depending on the rebound/damage incurred by the colliding objects.)
"For the tire rolling down the ramp, I concluded that gravitational potential energy must have experienced the greatest change since its decrease contributed to the increases in both translational kinetic energy and rotational kinetic energy?" (Yes.)
"Can you explain what happens to the rotational kinetic energy of the tire after it leaves the ramp?" (Since we ignore drag, the rotation of the tire is unaffected as it sails through the air, so its rotational kinetic energy remains constant.)
"I am doing my best to pass the quiz tomorrow. I am battling the pace of the class and also the 'flipped' structure (no need to reiterate my or your perspective on this). I really am trying to not hate physics."
"Enjoying the class so far."
"Would you rather be able to see 10 minutes into your own future or 10 minutes into the future of anyone but yourself?" (I'm not sure if it was better to have seen myself reading this question 10 minutes into the future, or to have seen you sending me this question 10 minutes into the future.)
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