Online reading assignment: free fall, vector components

Physics 205A, fall semester 2019
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 find the right variables for a problem by analyzing which parts of the information are given and which are not. I also understand how to determine which of the kinematic equations to use by determining which of the five variables needs to be found and how to rule out a variable that doesn't need to be found."

"Things can be thrown upwards (start with positive velocity), thrown downwards (start with negative velocity), or dropped (start with zero velocity)."

"During free fall, air resistance is neglected and the acceleration is nearly constant. Because acceleration is constant, we can use kinematic equations. Using a right triangle we are able to define sinθ cosθ and tanθ which helps us solve problems that involve angles. Scalars are numbers with magnitude such as time and volume while vectors are quantities with magnitude and direction such as displacement and velocity."

"I understand that an object can have a different vertical distance traveled than magnitude of vertical displacement. This is dependent on if the object is thrown straight in the air and then free falls, dropped into free fall, or thrown downward. I believe that the vertical displacement is equal to the distance if the object is dropped or thrown down, but the distance traveled is GREATER than the displacement if the object is thrown up."

"The fact that the only force acting on a ball falling down is gravity which has a constant acceleration is consistent with my understanding of physics. I also understand that vectors are determined by the x and y components in a triangle bringing us back to trigonometry.

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 was confused about how an object thrown or shot upwards can reach the same speed when it comes back down to its initial starting point as when it is thrown or shot downwards from its starting point."

"I found the homework problems a little bit confusing just because we haven't gone over many of those sorts of problems together. It would be very helpful to go over one of those specific problems in lecture."

"Trigonometry, but just a refresher would be useful.

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

"We assume that drag forces are negligible."

"Air resistance is ignored."

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 v_0y has a __________ value.

negative.	*********** [11]
zero.	********************************* [33]
positive.	*** [3]
(Unsure/guessing/lost/help!)	** [2]

For the boy, the vertical distance traveled is __________ the magnitude of the vertical displacement.

less than.	*** [3]
equal to.	************************************ [36]
greater than.	******** [8]
(Unsure/guessing/lost/help!)	** [2]

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 v_0y has a __________ value.

negative.	************************* [25]
zero.	********** [10]
positive.	********* [9]
(Unsure/guessing/lost/help!)	***** [5]

For the ball, the vertical distance traveled is __________ the magnitude of the vertical displacement.

less than.	***** [5]
equal to.	**************************** [28]
greater than.	****************** [13]
(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 v_0y has a __________ value.

negative.	**** [4]
zero.	****** [6]
positive.	*********************************** [35]
(Unsure/guessing/lost/help!)	**** [4]

For the hat, the vertical distance traveled is __________ the magnitude of the vertical displacement.

less than.	***** [5]
equal to.	*** [3]
greater than.	************************************** [38]
(Unsure/guessing/lost/help!)	*** [3]

Mark the level of your exposure to trigonometry (triangles, unit circles, inverse functions, Pythagorean theorem):

None at all.	* [1]
Slight.	*** [3]
Some.	********** [10]
A fair amount.	************************ [24]
A lot.	*********** [11]

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) [92%]
cos θ: (a/h) [88%]
tan θ: (o/a) [88%]
hypotenuse h length: √(o² + a²) [94%]

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

"Soh-cah-toa."

"Don't recall one."

"I've never heard one."

"I don't really use one."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"This is pretty cool. We are now moving into free fall which might start to make some things confusing and interesting when combining it with our horizontal motion knowledge."

"For the free fall examples above, would ground level be 0 or from when the ball left their hand?" (The convention used here is that we will always start at y = 0 at t = 0.)

"For all of the questions in this assignment, all of the initial velocities are zero? Because everything starts from not moving and is then thrown?" (If you throw a ball, it won't be in free fall (subject only to the force of gravity) until you let it go--so we can only start time t = 0 from the moment it was released with an initial velocity, as it leaves your hand.)

"Is there ever a setting where the free fall rules for falling objects don't apply?" (If air resistance (drag) is significant, then we can't say that acceleration is a constant value of 9.80 m/s² downwards.)

"In terms of this class are we to automatically assume drag/air resistance doesn't matter or will it be noted?" (On the quizzes and midterms, it will always be stated whether or not air resistance is negligible.)

"The last time I used SOH CAH TOA was 10th grade, so it's a little fuzzy."

"Will we only be using trigonometry to solve problems? I like calculus but I get lost when it comes to applying it to physics for some reason." (We'll use trigonometry to break down diagonal vectors such that we can analyze horizontal and vertical motion separately for projectile motion.)

"Nothing to ask here. Looking forward to the lecture!"

Online reading assignment: free fall, vector components

Physics 205A, fall semester 2018
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.

"I have a a way better understanding of the free fall concept and how gravity affects these objects when thrown in the air and when falling. It was good to have a review of vectors and the trigonometry that goes with calculating them! I feel I have a clearer understanding about what was discussed in class on Monday."

"How to interpret the given equations and use them to solve for an unknown value in a word problem. I also understand that you can manipulate each equation to solve for a different unknown when needed."

"Cosine and sine trigonometric functions allow the x- and y-components of a vector to be calculated."

"How trigonometric functions relate the angles and sides of a right triangle."

"When an object is undergoing free fall, only the force of gravity is pulling on it, so it experiences the acceleration due to gravity, with a magnitude of 9.80 m/s², and since the object is going in a downwards direction, it will always be a negative sign (if up is taken to be the positive vertical direction)."

"That we have to neglect drag on free fall."

"Sorry, I was very busy."

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'm not sure when to use the quadratic formula to find time. Also, a little discussion about vertical motion and signs/direction would be helpful."

"The equations. My brain has a harder time making sense of things when there are so many variables with different subscripts. It helps if I can write out a key with what each thing means."

"Some of the equations used were a bit confusing, mostly because I still need to learn the symbols of a lot of things we are learning."

"I would appreciate some review on free falling bodies and the different methods that come with the calculations. I have a better understanding of free falling bodies but i'm still not completely clear on the concept and i'd feel more confident if we discussed in class on Wednesday!"

"I need more explanation on how I assign the signs on the initial velocities for free fall."

"The vectors presentation was pretty confusing for me. I feel that I could use a better explanation."

"I found the vectors section confusing. I understand the steps/equations that are given and when to use them based on the info you have, but the trigonometric functions are unfamiliar to me."

"I don't quite understand the vectors. All the equations and things got to be a little much and I could use a little review in class."

"Nothing really confused me. I understood the basic concepts of everything."

"I'm sorry, P-dog."

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

"When in free fall there is only the force of gravity; there is no air resistance."

"Gravity is the only force affecting an object in free fall."

"When dealing with idealized motion, objects in free fall are not thought to be affected by drag (air resistance)."

"There is no drag on an object said to be in free fall."

"That air resistance is negligible."

"During free fall, it states that in an idealized motion, the air resistance is neglected and the acceleration is nearly constant."

"I have no idea."

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 v_0y has a __________ value.

negative.	********* [9]
zero.	*********************************** [35]
positive.	*** [3]
(Unsure/guessing/lost/help!)	** [2]

For the boy, the vertical distance traveled is __________ the magnitude of the vertical displacement.

less than.	** [2]
equal to.	***************************************** [41]
greater than.	**** [4]
(Unsure/guessing/lost/help!)	** [2]

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 v_0y has a __________ value.

negative.	********************************* [33]
zero.	******** [8]
positive.	****** [6]
(Unsure/guessing/lost/help!)	** [2]

For the ball, the vertical distance traveled is __________ the magnitude of the vertical displacement.

less than.	***** [5]
equal to.	********************************* [33]
greater than.	******** [8]
(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 v_0y has a __________ value.

negative.	*** [3]
zero.	******* [7]
positive.	************************************ [36]
(Unsure/guessing/lost/help!)	*** [3]

For the hat, the vertical distance traveled is __________ the magnitude of the vertical displacement.

less than.	** [2]
equal to.	****** [6]
greater than.	************************************ [36]
(Unsure/guessing/lost/help!)	***** [5]

Mark the level of your exposure to trigonometry (triangles, unit circles, inverse functions, Pythagorean theorem):

None at all.	* [1]
Slight.	**** [4]
Some.	***** [15]
A fair amount.	**************** [16]
A lot.	************* [13]

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) [88%]
cos θ: (a/h) [90%]
tan θ: (o/a) [88%]
hypotenuse h length: √(o² + a²) [86%]

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

"Soh-cah-toa."

The CAST rule is the way I memorize (positive) trigonometric functions."

"I do not remember them. "I do not have a mnemonic device to memorize any right-triangle trigonometric relationships."

"I just memorized the relations and studied each one because I had to know them."

"I do not use one currently but I would like to learn one."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"when you throw a ball downwards the graph is considered to have a negative initial velocity correct? However would the vertical distance traveled be considered to be equal to the magnitude of vertical displacement? Since we don't have a positive initial velocity and the object is dropping from its initial to its final position without rising at any point, then that drop is considered a 'straight line' if you will, hence the vertical distance traveled should be equal to magnitude of vertical displacement right? (Yes, yes, yes.)

"If you could go over the answers for the questions regarding the vertical distance traveled that would be great."

"We need to go over distance vs displacement again, specifically when it is implied with these problems about free-fall." (We certainly will.)

"I know where we can see our quiz grades, but how do we keep track of the points we earn from quiz extra-credit, post-labs, reading assignments, and homework reports?" (All those points are also posted on the same page as the quiz scores. (Lab points will be posted separately, later.))

"Will we only be using the first quadrant?"

"Could you go into vector components a little more? The book makes it kind of confusing."

"Please help on the trigonometry part of this lesson!"

"How far in depth are we going to get into trigonometry? (For now, not that far. We'll use more trigonometry, and review more of it later on, as needed.)

"Is drag the equivalent of friction but in a vertical sense?" (Yes, in the sense that it is a force that always acts against the motion of an object.)

"I am getting better at this style of teaching but it is still taking time to get used to. Personally I think I just do better when material is covered more in class than at home." (I will try to cover as much stuff in class that you tell me that you need to know.)

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 v_0y 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 v_0y 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 v_0y 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."

Online reading assignment: free fall, vector components

Physics 205A, fall semester 2016
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 the constant acceleration equations we use are the same for either horizontal or vertical direction."

"Free fall is basically what would happen if there was only gravity working as a force on falling objects. However, since there is air resistance and other factors free fall can only happen in a vacuum."

"In the reading assignment examples, the boy going cliff-jumping begins with a zero initial velocity. An object thrown up begins with a positive initial velocity and when thrown down, a negative initial velocity."

"How the acceleration for a free fall object is known, due to it being the constant acceleration of gravity."

"Trigonometric functions sine, cosine and tangent of angle θ are used in an equation with the lengths of the opposite or adjacent side, and the hypotenuse. Adding together vector components gives the overall vector magnitude."

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 didn't find too much confusing, maybe just need a refresher on the trigonometry."

"I really did not understand vectors. I think I need to brush up on my trigonometry."

"The only thing I found sort of confusing was on the presentation review the questions where it asked if the vertical distance traveled is less than, equal to, or greater than the magnitude of displacement. None of those ones really made sense to me."

"The part that I found a little confusing in this section is the difference between free falling and when the object is being thrown up or down. I am unsure if there is a difference in initial velocity and if that changes the equation that would be used."

"I don't understand how a pellet fired in the downward direction from the edge of a cliff would strike the ground with the same speed as a pellet fired in the upward direction. Fired in the downward direction, the acceleration and velocity would be acting in the same direction, while acting in opposite directions if fired upward. Are the speeds the same at ground impact because the pellet shot upward gains enough speed due to acceleration on the way down to match the acceleration and velocity of the one fired downward?" (Yes.)

"The vertical distance traveled versus the magnitude of vertical displacement of an object thrown downwards. It's still traveling the same distance as something falling from rest, but the velocity is negative so does that mean the magnitude of vertical displacement is different just because it was falling faster?" (No, vertical distance traveled would be equal to the magnitude of vertical displacement, as there is no back-and-forth motion.)

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

"In free fall motion, air resistance is neglected, such that vertical acceleration is constant."

"That the drag forces are negligible and need not be recorded."

"Air resistance is almost insignificant to where it is negligible when gravity is the main force pushing down on an object."

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

The v_y(t) graph has __________ initial velocity v_0y.

a negative.	***** [5]
zero.	***************************************** [41]
a positive.	[0]
(Unsure/guessing/lost/help!)	* [1]

For the boy, the vertical distance traveled is __________ the magnitude of the vertical displacement.

less than.	****** [6]
equal to.	************************************ [37]
greater than.	* [1]
(Unsure/guessing/lost/help!)	*** [3]

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

The v_y(t) graph has __________ initial velocity v_0y.

a negative.	************************* [25]
zero.	********* [9]
a positive.	*********** [11]
(Unsure/guessing/lost/help!)	** [2]

For the ball, the vertical distance traveled is __________ the magnitude of the vertical displacement.

less than.	***** [5]
equal to.	************************ [34]
greater than.	** [2]
(Unsure/guessing/lost/help!)	****** [6]

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

The v_y(t) graph has __________ initial velocity v_0y.

a negative.	*** [3]
zero.	******* [7]
a positive.	********************************** [34]
(Unsure/guessing/lost/help!)	*** [3]

For the hat, the vertical distance traveled is __________ the magnitude of the vertical displacement.

less than.	****** [6]
equal to.	********** [10]
greater than.	**************************** [28]
(Unsure/guessing/lost/help!)	[3]

Mark the level of your exposure to trigonometry (triangles, unit circles, inverse functions, Pythagorean theorem):

None at all.	[0]
Slight.	***** [5]
Some.	************ [12]
A fair amount.	****************** [18]
A lot.	************ [12]

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) [91%]
cos θ: (a/h) [91%]
tan θ: (o/a) [94%]
hypotenuse h length: √(o² + a²) [91%]

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

"Soh-cah-toa."

"I burned an image of a right triangle into my brain over the course of a summer trigonometry class."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Can you please go over more math in class?"

"Can you go over the trigonometric functions real quick? Thanks."

"I honestly can't think of a question right now."

"Will there be any material on the quizzes/midterms that we will not/do not cover in class? I'm assuming everything from the blog examples and the assigned problems in the textbook can be asked on quizzes and exams." (Your assumption is correct--your quizzes and midterms should reflect the level of understanding asked for from your in-class work, blog examples, and textbook homework.)

"Can we go over the EMAS stopping distance of a Boeing 727 final exam question?"

Physics presentation: free fall

This is only just a little disturbing, but I can't stop watching this. (Movie link: "experiment with apples.")

So let's try to analyze this and similar types of motion--free fall--using graphs and equations from our one-dimensional motion toolbox.

Our working definition of free fall is an object that is subject only to the force of gravity. Nothing in contact with it, nor any drag (although we often make the assumption that drag forces are negligible).

So let's take a look at how the kinematic equations turn out for free fall motion.

We'll consider the convention where up is the positive vertical direction. (If you're the type that likes to call down positive, you're just being contrary and weird.) Since an object in free fall is only experiencing the force of gravity, then it will experience the acceleration due to gravity (of magnitude 9.80 m/s²), which is directed downwards, and thus requires an obligatory negative sign.

Note that our vertical motion equations will then have a vertical acceleration a_y = –9.80 m/s². Again, that obligatory negative sign (also we'll assume that the starting position is y₀ = 0 m at t₀ = 0 s).

Also the quadratic formula will often be useful as well for free fall.

Let's take a look at every conceivable vertical velocity v_y vs. t graph there could possibly be for any type of free fall situation.

But don't worry, there are only three possible graphs. Notice that they have all have the same negative slope--and since the slope of a velocity versus time graph is acceleration, these graphs all have the same acceleration a_y = –9.80 m/s². The only difference between these graphs is the initial vertical velocity v_0y, whether positive (thrown upwards), zero (and thus released from rest), or negative (and thus thrown downwards).

So let's take a look at some situations, and decide which free fall graph best describes them (assuming we can neglect drag).

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

The v_y(t) graph has __________ initial velocity v_0y.
(A) a negative.
(B) zero.
(C) a positive.
(D) (Unsure/guessing/lost/help!)

The vertical distance traveled is __________ the magnitude of the vertical displacement.
(A) less than.
(B) equal to.
(C) greater than.
(D) (Unsure/guessing/lost/help!)

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

The v_y(t) graph has __________ initial velocity v_0y.
(A) a negative.
(B) zero.
(C) a positive.
(D) (Unsure/guessing/lost/help!)

The vertical distance traveled is __________ the magnitude of the vertical displacement.
(A) less than.
(B) equal to.
(C) greater than.
(D) (Unsure/guessing/lost/help!)

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

The v_y(t) graph has __________ initial velocity v_0y.
(A) a negative.
(B) zero.
(C) a positive.
(D) (Unsure/guessing/lost/help!)

The vertical distance traveled is __________ the magnitude of the vertical displacement.
(A) less than.
(B) equal to.
(C) greater than.
(D) (Unsure/guessing/lost/help!)

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 v_x(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 v_y(t) graph has __________ initial velocity v_0y.

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 v_y(t) graph has __________ initial velocity v_0y.

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 v_y(t) graph has __________ initial velocity v_0y.

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)