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 collisions.
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.
"There are three different types of collisions: completely inelastic, partially inelastic, and elastic. And each of these collisions can either conserve or not conserve kinetic energy."
"An inelastic collision is where the kinetic energy is not conserved. A completely inelastic collision is where it sticks together afterward, while partially inelastic collisions deform but don't stick together afterwards."
"The differences between inelastic and elastic collisions and how to identify them. Inelastic collisions (partial or complete) do not conserve kinetic energy, while elastic collisions do."
"An elastic collision is where two objects rebound and there is no permanent damage. Also, only elastic collisions conserve kinetic energy since there is no damage."
"Momentum is conserved for any collision as long as it is brief, the time is so short it becomes zero. Kinetic energy is conserved during elastic conclusions."
"When collisions happen during a very short period of time the left side of the momentum conservation equation can be set to 0. Basically when you are looking at a collision that happens in a short period of time you are just examining the exchange in momentum between the two objects."
"The different types of collisions and the rules for colisions. The conservation laws and the flowchart for them made perfect sense to me."
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.
"The flowchart in the presentation was hard to understand. Also, the equation for momentum conservation look intimidating."
"I was confused by the principle of conservation of linear momentum."
"The equation for the conservations kind of confusing. I would just like to see examples worked out in class."
"I had a little trouble understanding the difference between elastic and inelastic collision. Elastic collision is when two objects collide head on and no heat or other form of energy is produced during the collision. Inelastic collision have some thermal and sound energy produced so kinetic energy is not conserved?"
"Categorizing collisions and determining kinetic energy conservation (I did read kinetic energy is only conserved for elastic collisions because none is permanently lost in deformation). Applying conservation law(s) for collisions."
"What I found confusing was why partially inelastic has kinetic energy lost but I think I understand it now."
"When we read the question it is very important to understand what happens after colliding. Sometimes I get confused about this."
"I understood everything in the presentation/textbook...for now anyway."
"I actually understood what this reading assignment was about."
Explain the difference between a (partially) inelastic collision and a completely inelastic collision.
"A partially inelastic collision is where two objects bounce off of each other. A completely inelastic collision is where objects do stick to each other. Permanent damage is present in both cases."
"A partially inelastic collision is when two objects rebound off each other but there is some permanent damage afterwards and a completely inelastic collision is when two objects collide but they stick together."
"A partially inelastic collision has a small rebound with damage and a completely elastic collision has no rebound and the two crashing objects become 'stuck' to each other."
Explain why drag, friction, and other external forces do not matter during sufficiently "brief" collisions, in order for momentum to be conserved.
"The time is so small that the friction is negligent."
"We can neglect their impulses because the brief collision occurs in an instant, so δt would be zero."
"External forces/impulses would be negligible in the relatively brief time that collisions occur."
"Because collisions happen in such a brief time, external forces do not factor."
"These 'brief' collisions happen in a fraction of a second so even though these forces can be quite large their impulses are negligible because of the amount of time they take place in. So momentum is conserved because the objects will only exchange momentum."
Completely inelastic. * [1] (Partially) inelastic. ********************************* [33] Elastic. ** [2] (Unsure/lost/guessing/help!) * [1]
Completely inelastic. ** [2] (Partially) inelastic. ***** [5] Elastic. **************************** [28] (Unsure/lost/guessing/help!) ** [2]
Completely inelastic. ******************************* [31] (Partially) inelastic. *** [3] Elastic. ** [2] (Unsure/lost/guessing/help!) * [1]
Completely inelastic. *** [3] (Partially) inelastic. *********************** [23] Elastic. ******* [7] (Unsure/lost/guessing/help!) **** [4]
Completely inelastic. ***** [5] (Partially) inelastic. ************ [12] Elastic. *************** [15] (Unsure/lost/guessing/help!) ***** [5]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"How can you tell if something gets damaged during a collision, such as when firing a gun? Should we just have real-world knowledge or should we know this from examples?" (You'll practice this in class; basically any process that removes or adds kinetic energy counts as "damage.")
What would be the collision if the object went through the other object, for example a bullet going through another object." (That counts as "damage," and since the bullet and object are not stuck together afterwards, then this would be a partially inelastic collision. (If the bullet was embedded in the object, such that they are "stuck together," then this would be a completely inelastic collision.)
"Kinetic energy is all lost when you have completely inelastic collision?" (Well, not all of it is lost, but enough of it is lost such that the objects stick together (rather than rebounding) after the collision, even if they both still have some motion together afterwards.)
No comments:
Post a Comment