## 20141022

### Online reading assignment: torque and rotations

Physics 205A, fall semester 2014
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 torque and rotations.

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.
"Torque is the twisting by a force that tends to cause rotation."

"Torque is the product of force (N) and the length of the perpendicular lever arm (m). The force vector (line of action) is perpendicular to the perpendicular lever arm."

"N1 applies to torque when the object is in equilibrium. N2 applies when the object is starting to rotate."

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.
"Net torque."

"How an object can have a net force of zero while the torque is nonzero. I also do not get how if its torque was nonzero and net force was zero, how such an object could have a nonzero angular acceleration."

"I am not 100% on drawing out a diagram for torque."

"Line of action for a force."

"The lever arm, and how it was drawn/what function it serves."

What is the SI (Système International) unit for torque?
"N·m."

"Tau."

"Newtons."

Briefly describe how the line of action should be drawn for a given force.
"The line of action should extend along the force vector direction."

"I have no idea."

"With a dashed line."

When a lever arm (or moment arm) is drawn, briefly explain where it starts, and how it should intersect the line of action for a force.
"The lever arm starts at the rotation axis and is perpendicular to the line of action."

"I have no clue. Sorry."

For the stuck wrench (assuming that it is rigid and not flexing), Newton's rotational __________ law applies, and the clockwise torques and counterclockwise torques acting on the wrench are __________.
 first; balanced. ************************************************* [49] second; unbalanced. ********* [9] (Unsure/lost/guessing/help!) ***** [5]

For the crane, Newton's rotational __________ law applies, and the clockwise torques and counterclockwise torques acting on the crane are __________.
 first; balanced. ******** [8] second; unbalanced. ************************************************* [49] (Unsure/lost/guessing/help!) ****** [6]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I once broke a torque wrench trying to loosen the lug nuts on a Lexus. They must have been torqued up to 200 ft·lbs. Apparently, they don't want you to do anything to their cars at all." (Unless you had a Nutcracker®.)

"Can you go over how to draw diagrams for these problems? Can you please go over the 'line of action?'" (Yes, and yes.)

"I apologize for turning in such a shameful assignment. I will definitely read the material before class, so I can follow what is going on."

"Does the extra credit from lab count as a part of the total extra credit for the class?"(No, lab points are capped at a 100 points maximum.)

"Would it be possible to do a really good review for the upcoming quiz?" (Let's see how well you can rock the sample quiz from last year.)

"Didn't think it could get any harder. You must be mad smart."

"I think I am going to like this section."