## 20170911

### Online reading assignment: free fall, vector components

Physics 205A, fall semester 2017
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 presentations on free fall and vector components.

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.
"How to choose an equation based on the variables provided and the unknown value we are solving for. I understand the concept of the free falling object equations and when initial velocity is positive, negative, or zero."

"I feel like the presentation was fair enough to understand. The formulas seem mostly self-explanatory with the potential problems we will see."

"Regardless of the type of equation, you will always be solving a problem by using what you have to plug in and figuring out the unknown."

"Math is my strong point, so I'm good about plugging things in to get an answer. However, not always good about figuring when to use a certain equation."

"That the acceleration due to gravity is –9.80 m/s2 and is considered constant. This means that in free-fall situations our acceleration value would be replaced with the constant of –9.80 m/s2. This also means that any x-value for our "list of five" kinematic equations would be replaced with a y-value instead."

"Free fall is any motion of an object where gravity is the only force acting upon it; air resistance is neglected and the acceleration is nearly constant. I think I will do better with the trig than the calculus."

"I understand the trigonometry section. How to use either two sides of a triangle to find an angle, or using a side and an angle to find the value of another side."

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.
"Applications of vectors and their components seems to strike me as a but confusing. But I'm sure as I practice them in class and on my own I will grasp this concept better as it is based around trig. Also clarification on free falling and the introduction of vertical velocity would be helpful."

"I do not understand negative vectors. I guess they are just the opposite value of the positive?"

"I am getting confused when comparing vertical velocity graphs. I need more clarification on which graph is associated with the different types of vertical movement."

"I find the most confusing thing in the reading is to put a picture to what is actually going on. Once you get a picture its a little easier."

"Vertical distance traveled vs magnitude of vertical distance traveled. Is the magnitude just the absolute value of vertical distance traveled?"

"I would just like to go through using the equations in class."

"I did not find anything in the chapter reading confusing."

"Not sure what I do and don't find confusing at the moment."

Explain what assumptions are made about the amount of drag (air resistance) on an object said to be in free fall.
"It is usually zero."

"That it is negligible."

A boy steps off of a ledge (with no initial vertical velocity) and splashes into the water below.

Choose up to be the +y direction. The initial vertical velocity v0y has a __________ value.
 negative. ******* [7] zero. ******************************** [32] positive. * [1] (Unsure/guessing/lost/help!) * [1]
For the boy, the vertical distance traveled is __________ the magnitude of the vertical displacement.
 less than. *** [3] equal to. ************************************* [37] greater than. * [1] (Unsure/guessing/lost/help!) [0]

A ball is thrown and released downwards from the top of a building, and hits the ground below.

Choose up to be the +y direction. The initial vertical velocity v0y has a __________ value.
 negative. *************************** [27] zero. ** [2] positive. ********** [10] (Unsure/guessing/lost/help!) ** [2]
For the ball, the vertical distance traveled is __________ the magnitude of the vertical displacement.
 less than. ********** [10] equal to. ************************ [24] greater than. **** [4] (Unsure/guessing/lost/help!) *** [3]

A hat is thrown and released upwards into the air and lands on the grass below.

Choose up to be the +y direction. The initial vertical velocity v0y has a __________ value.
 negative. ** [2] zero. *** [3] positive. ************************************ [36] (Unsure/guessing/lost/help!) [0]
For the hat, the vertical distance traveled is __________ the magnitude of the vertical displacement.
 less than. ***** [5] equal to. ***** [5] greater than. ****************************** [30] (Unsure/guessing/lost/help!) * [1]

Mark the level of your exposure to trigonometry (triangles, unit circles, inverse functions, Pythagorean theorem):
 None at all. [0] Slight. **** [4] Some. ************** [14] A fair amount. ************* [13] A lot. ********** [10]

Indicate the following trigonometric relations between angle θ, the opposite leg o, the adjacent leg a, and hypotenuse h for a right triangle. (Assume that the angle θ is in the first quadrant: 0° ≤ θ ≤ 90°.)
(Only correct responses shown.)
sin θ: (o/h) [98%]
cos θ: (a/h) [98%]
tan θ: (o/a) [98%]
hypotenuse h length: √(o2 + a2) [98%]

Describe what mnemonic device (if any) you use to memorize the right-triangle trigonometric relationships.
"Soh-cah-toa."

"I don't really have one."

"I usually sing a song that I made up."

"Some Old Hippy Caught Another Hippy Trippin' On Acid."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"When discussing vectors what exactly is magnitude? I understand when we are talking about something like magnitude of acceleration it is just another way of saying the absolute value, but is that same thing as the magnitude in a vector?" (Magnitude is just the length of a vector. If the vector is just a horizontal or just a vertical line, magnitude is just the length of that horizontal or that vertical line. If the vector is diagonal, then magnitude is just the length of that diagonal line (in which case the diagonal line is the hypotenuse of a triangle of horizontal and vertical components.)

"Why is math so hard?"

"How much pre-existing math knowledge will I need for the entire course?" (Officially, you're responsible for everything that is listed in the math pre-requisites for this course. However, we'll try to briefly go over these skills in class when you start to need them (e.g., trigonometry).)

"Can you show the correct answers to the questions you have here in the assignment after completing them? It would be nice to see the answers to the questions on this page for study tools later on." (The answers to the previous reading assignment are always posted within 12 hours after it closes; and part of every future reading assignment is to go to the links provided to review those answers.)

"I feel I am not learning as much as I could be from the flipped class."

"Can you spend more time on lecture in class? It's a lot of material to understand on my own." (It is a lot to try to understand on your own before class. But see the comments below.)

"Please start lecturing in class to explain the information in the book. I have personally had conversations with others in the class and the majority are lost and have no idea what is going on. Reading and learning from a book is fine for a history class but not for something as complicated as physics." (I understand that the textbook is overwhelming to learn from as a primary resource. That said:
1. the textbook is to be used for background and terminology (as indicated by the notes under each reading assignment ("This is a preview...," "At least know how to calculate...," "See how these are applied...," and "Review these relationships...," etc.);
2. the presentation slides will emphasize the important parts you need to know; and
3. you will only be tested on the knowledge that is ultimately applied on the in-class worksheets, homework problems, and sample exam problems.
In short: there isn't time to teach everything in the textbook, there isn't time to learn everything in the textbook, so you won't be tested on everything in the textbook. So I'll be straight with you on what there is time to teach and to learn, and what you will be tested on.)

"I would like to be able to access the surveys for both Monday and Wednesday before the end of the weekend instead of only after the lecture has been given. If we're having to do these before the lecture on the topic is given either way, I find it really inconvenient that I can't answer questions for both Monday and Wednesday ahead of time. And I end up doing everything last minute instead." (I know there is bit of a squeeze between Monday and Wednesday's lecture to do reading assignment before Wednesday's class (where you have two nights to complete it), compared to the reading assignment due before Monday's class (where you have five nights to complete it). But the assigned textbook chapters and presentation slides for either Monday or Wednesday assignments are always posted at least a week ahead of time, sometimes two weeks ahead.)

"Let's LEARN."