## 20140910

### Online reading assignment: projectile motion, forces/interactions

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 projectile motion and forces/interactions.

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.
"I understand the concept of projectile motion. At first I thought that the horizontal velocity was slowly decreasing, but in actuality it's a constant with the force of gravity only acting on it vertically."

"Projectile motion is a special free fall situation in which the object in motion has a horizontal component and a vertical component that operate separately from one another. The horizontal velocity is constant throughout the motion, and the vertical velocity is continuously changing, causing the projectile to move in a parabolic fashion."

"Honestly I read it and I just don't get it."

"I understood everything fine it was pretty interesting."

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.
"Because I'm not yet able to devote as much time to really sit down and read, study, and focus everything is confusing to me because I can't really focus and work through things and really see what I get and don't get, I just get frustrated and everything is confusing."

"I found that the formulas took me a little while to understand. This means knowing what variable represented what and what its effects on the overall problem was."

"A little more on trajectories could be helpful. The tips and tricks."

For all possible cases of an object during ideal projectile motion, its horizontal speed will be:
 decreasing. ** [2] constant. ************************************************ [48] increasing. * [1] (More than one of the above choices.) * [1] (Unsure/guessing/lost/help!) *** [3]

Describe a situation with a negative (starting) angle of elevation for projectile motion.
"I don't know--I'm frustrated, I feel 'grrr' because I can't think of an example."

"If the projectile were shooting downward the angle of elevation would be negative."

"The object is aimed towards the ground."

Identify the type of interaction ("force") with its symbol. (Only correct responses shown.)
Weight ("gravitational force") : w [89%]
Surface contact force ("normal force"): N [89%]
Tension ("rope/cable/string force"): T [96%]
Kinetic friction ("sliding force," or "sliption"): fk [96%]
Static friction ("sticking force," or "stiction"): fs [95%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Can all forces be broken down into horizontal and vertical components? It seems like with some forces, it would be impossible to determine how much of the force is in the x- vs the y- directions." (Any force, like all other types of vectors (velocity, etc.) can be broken down into horizontal and vertical components.)

"How exactly is extra-credit factored into our grades? What end percent does it serve as a buffer?" (Extra-credit points (from group "scratcher" quizzes and other online surveys) are worth a maximum of 25 points, which is one-quarter of a letter grade. Extra-credit points in laboratory are applied only towards your laboratory points.)

"When looking at the Quiz 1 grade postings, what happened to the first group quiz 'scratcher?'" (It's there, under the "Group quiz 1 (G1)" column header.)

"What do you suggest we study in order to have success on Quiz 2?" (The study guide for the upcoming quiz is posted on this week's announcements. Also we'll have a practice quiz from a previous semester, in class.)

"Do we need to memorize these formulas?" (You don't need to memorize the equations that are already provided for you on the quiz. The emphasis is on knowing how/when to use them.)

"On average how often would you say you use your smartphone?" (All the time. Right now, in fact, as I'm typing this.)