## 20141006

### Online reading assignment: impulse and momentum

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 impulse and momentum.

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 momentum vector depends on both mass and velocity. Impulse is the product of the net force acting on an object and the time that the force acted on the object."

"I understand that two things can have the same velocity, but their momentum can be very different. For example a car moving at the same speed as a semi-truck has less momentum, because it has a smaller mass."

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 really don't know about the impulse-momentum theorem. I kind of understand what it's talking about,but I don't understand it when using it to apply it to situations."

"I did not find any concepts confusing from this chapter."

"I understand how to calculate impulse, but I don't quite understand exactly what it is, and why it matters. I think the fact that it is called impulse is confusing."

"Impulse does not make sense to me."

"Why is impulse not measured in joules as opposed to newton-seconds?"

For the child hitting the tee ball with a bat, if the bat is swung such that it exerts the same net force on the tee ball for a longer time (by giving the bat more "follow-through"), the impulse on the tee ball will be __________, and the change in momentum of the tee ball will be:
 less; less. *** [3] less; more. ********* [9] more; less. ******** [8] more; more. ******************************* [31] (Unsure/lost/guessing/help!) ********** [10]

Indicate which crash-test dummy (if any) has the greater magnitude quantity in the process of coming to a complete stop. (Only correct responses shown.)
Greater magnitude momentum change ∆p: (there is a tie). [23%]
Greater magnitude impulse "J" exerted on it: (there is a tie). [11%]
Longer stopping time ∆t: seatbelt and airbag. [34%]
Greater magnitude net (stopping) force ΣF: no seatbelt/airbag. [21%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Impulse 'J' is a mystery to me. Can we go over all of the definitions in class, please?" (Yes, I was going to go over some of the energy conservation homework questions, but after looking over the class' responses to the crash-test dummy questions, you really need a lot of help on understanding impulse and momentum.)

"I went bowling yesterday, but I didn't bowl any strikes with a ping-pong ball." (Sounds like you acquired an experimental verification of how momentum must also include mass as well as the velocity of an object.)

"How long is the midterm? How do you suggest a student prepare for the midterm in order to do well?" (We'll discuss details about the midterm through this week, and review certain topics as well.)

"Is there anything I can do to make the GIFs flow better? I only see frames and I feel I'm not getting the full example." (Some of them are quite large, so the frame rates are dropped in order to keep them from killing your bandwidth. YMMV.)

"Are these questions actually anonymous?" (Uh, who is this? More seriously, comments/questions here are anonymous to the other students, and to me as well unless there is a specific need to look up your information and reply privately to you.)