## 20150831

### Online reading assignment: free fall

Physics 205A, fall semester 2015
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 free fall.

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 list of five kinematic equations are built from the concepts of position, velocity, and (constant) acceleration. They can be used to solve application problems, and you'll need values for three out of the four variables for each equation. x(t), and vx(t) graphs can be used to show changes in velocity and constant acceleration."

For free fall we can use the same five kinematic equations from horizontal motion, but substitute y for x for the vertical direction. Acceleration is the rate at which the velocity is changing, so they do not necessarily behave the same in vertical motion."

"What acceleration, and that the constant acceleration due to gravity is -9.8 m/s2. I can correlate acceleration, velocity and position graphs."

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.
"Nothing was too challenging. If I had to say something was confusing, it would be the relationship of velocity and acceleration for the free fall graphs."

"Setting up my equations for the problems--I'm not sure if I'm plugging in the correct variables for the practice problems that were given."

"It was a little difficult to understand the equations. It just takes me a little while to go over them until I understand what the variables mean and when to use each equation."

"I am still having trouble picking the right equation for a problem as well as doing the algebra to isolate my unkown. I am working on this on my own."

"I don't understand what it means by the 'magnitude of displacement.' I believe this is a concept you already went over in lecture, but I could use a little more explanation to grasp an understanding."

"The idea of a slope at an instantaneous point makes sense to me, but if delta T is zero, you have a point, and a point has no slope. I get that it's a limit, and that it's as delta T approaches zero, but still. This was all I could come up with without saying that simple algebraic errors are normally my downfall."

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

"Assume that there is none."

"I could use more lecture about this topic. I'm not clear about air resistance."

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

The vy(t) graph has __________ initial velocity v0y.
 a negative. **** [4] zero. ***************************************************** [53] a positive. **** [4] (Unsure/guessing/lost/help!) ** [2]
The vertical distance traveled is __________ the magnitude of the vertical displacement.
 less than. * [1] equal to. ************************************************** [50] greater than. ****** [6] (Unsure/guessing/lost/help!) ****** [6]

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

The vy(t) graph has __________ initial velocity v0y.
 a negative. *********************************** [40] zero. ******* [7] a positive. ************ [12] (Unsure/guessing/lost/help!) **** [4]
The vertical distance traveled is __________ the magnitude of the vertical displacement.
 less than. ******** [8] equal to. ***************************************** [41] greater than. ******* [7] (Unsure/guessing/lost/help!) ******* [7]

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

The vy(t) graph has __________ initial velocity v0y.
 a negative. ******* [7] zero. ****** [6] a positive. *********************************************** [47] (Unsure/guessing/lost/help!) *** [3]
The vertical distance traveled is __________ the magnitude of the vertical displacement.
 less than. ********* [9] equal to. ********** [10] greater than. *************************************** [39] (Unsure/guessing/lost/help!) ***** [5]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"would very much like to see a few example problems done in class. One of my struggles at the moment is setting up problems." (Yes, as time allows, we can go through setting up problems--keep in mind that the worked-out portions and solutions are already posted online for each of these examples.)

"Are we expected to memorize the kinematic equations?" (No. Those are all listed at the end of each worksheet packet, and also at the bottom of the quizzes (and exam cover sheets.)

"Is there any way to go over distance traveled versus displacement? Can distance traveled ever be less than displacement?" (Whuuut--distance traveled can never be less than displacement.)

"I'm really confused...please help!" (Ask me questions when I circulate during class. Talk to me after class. See me in scheduled office hours. Make an off-schedule office hour appointment. E-mail me. #doallthethings)