Online reading assignment: energy conservation

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 a presentation on energy conservation.


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 easiest concept for me to understand from the reading and slide is the fact that translational kinetic energy is directly correlated to speed, in that if speed increases, so does translational kinetic energy."

"Gravitational potential energy is the energy that an object of mass has by its position in relation to the surface of Earth measured by the height of the object and an arbitrary zero level."

"I think gravitational potential energy is the easiest energy type to identify. If an object is 2 m off the ground then it has more gravitational potential energy than if the same object were 1 m off the ground."

"The gravitational force can do negative and positive work and that only the initial and final position should be considered when solving problems. This is also why it is considered a conservative force. Also, the greater the height, the greater gravitational potential energy is."

"A conservative force is not dependent on the path between start and finish points. Therefore, these types of forces also equate to zero work if the start and finish are the same."

"Conservative force is when the work done on an object is independent from the path taken between the initial and final heights, or when it does no net work on an object on a closed path. Nonconservative force is when the work done on an object moving between two points does depend on the path of motion, as we see with force of friction, air resistance, tension, etc."

"The basics of gravitational and elastic potential energy. And how they are combined with the change in translational kinetic energy in transfer balance equation."

"When a spring is pulled back it causes the energy to be stored and once released it shoots out."

"I have learned that elastic potential energy, translational kinetic energy and gravitational potential energy all play a part in non-conservative and conservative work. As the height of where an object is increases, so does its gravitational potential energy. As a slingshot is stretched back with a rock in the sling, the elastic potential energy increases. As it is fired off, the translational kinetic energy increases, and elastic potential energy decreases."

"This specific topic was kind of a blur, not gonna lie. I understand conservative forces and how how they can store energy and later retrieve without loss, and the opposite for nonconservative energy. That makes sense, but what doesn't is the application of information into the equations."

"Not much."

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 am a little unsure if the translational kinetic energy is simply increased as an object's movement or speed increases."

"Translational kinetic energy is difficult to comprehend on a practical level."

"Applying the equations to gravitational potential energy and elastic potential energy. Also need better clarification of conservative and non-conservative work."

"The transfer-balance equation and how to use it."

"I would like an example of using the transfer-balance equation in class because I am still confused on how to properly implement it into my problem-solving."

"I found the transfer-balance equation slightly confusing at first but then soon realized that its a total energy conservation equation. Other than that I did not find anything else confusing."

"I found it confusing to apply the certain types of energies to certain problems. For example, when do you use potential energy, kinetic energy, and/or mechanical energy? I understand the differences of the three. However, will a question on a test ask us to find one of these or a few of these or will we have to decide that based on the problem? "

For the woman moving upwards after being catapulted, her translational kinetic energy __________ while her gravitational potential energy __________.

decreases; increases.	*************************************** [39]
increases; decreases.	********* [9]
(Unsure/lost/guessing/help!)	* [1]

For the ball bearing being launched by the slingshot, its translational kinetic energy __________ while the elastic potential energy of the slingshot bands __________.

decreases; increases.	********** [10]
increases; decreases.	************************************** [38]
(Unsure/lost/guessing/help!)	* [1]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, indicate the changes in each her of energy forms. (Only correct responses shown.)

Translational kinetic energy: increases. [80%]
Gravitational potential energy: decreases. [74%]
Elastic potential energy (of the bungee cords): increases. [76%]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, the energy form that experienced the greatest amount of change (increase or decrease) was:

her translational kinetic energy.	************* [13]
her gravitational potential energy.	*************** [15]
the elastic potential energy of the bungee cords.	**************** [16]
(Unsure/lost/guessing/help!)	***** [5]

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

"How do we know when something is non-conservative and conservative?"

"For the examples above, they were cases of either an increase of kinetic energy and decrease of gravitational potential energy, or vice versa. Is it possible the have increase-increase or decrease-decrease?" (Only if there was (positive) work be done to add energy to the system, or (negative) work being done to remove energy from the system. Otherwise if there are only two types of energy and no work being transferred to/from the system, then an increase in one type of energy must be fed by a corresponding decrease in the other type of energy, and vice versa.)

"For the woman on the bungee swing, how are we supposed to know which energy experiences the greatest amount of change without numeric values?"

"Will there be a study guide for the midterm that's a little more structured on the key concepts we need to know? Or do we just have to shuffle through our quizzes and homework, etc.?" (Go through the list of example midterm questions on next week's announcements page. The idea is that the methods and concepts used to answer those examples is what you would need to apply to answer your upcoming midterm.)

"Having a hard time understanding the textbook, YouTube is my friend but also sometimes my enemy."

"Can we do an end of the year potluck?" (The final exam is basically a "knowledge potluck." Everyone should bring something.)

Online reading assignment: work and energy

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 a presentation on work and energy.


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.

"Work is the result of the magnitude of force times the magnitude of displacement of an object. Because displacement must be present, work does not apply to immovable objects. "

"How translational kinetic energy increases or decreases depending on if work is done on or against the object."

"Work is the magnitude of the force times the magnitude of the displacement and does not have direction, therefore, it is a scalar quantity. If an object does not move, then the force acting on the object does no work. When the force and displacement do not point in the same direction, only the component of the force along the displacement is used to find work."

"Work is scalar meaning there is no direction necessarily. There are two facets of work, as it comes positively and negatively. Positive work indicate the work done on the object, and negative work indicates the work done by the object. If an object is in constant motion, then the net positive and negative work equal zero. Work on a moving object dependent on the direction means the net positive work is greater than the negative work. We can use the work-energy theorem which is essentially W=1/2mvf^2 and can be manipulated to find certain values however you life. Giving you the ability to find the values necessary to complete a problem."

"Oh boy. This one was a doozy! So first, the textbook talked about joules. I like joules. They’re simple enough, made sense. THEN the textbook talked about Kinetic Energy, how that relates to the kinematic equations, how we factor in Newton’s second law and some of the theory behind forces. FINALLY it drops the bomb of two very involved problems. My mind was blown, and I’ll need the next 48 hours to process how I feel."

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 a little confused on how we're supposed to apply kinematics for kinetic energy and work. Are we trying to find a velocity? is it given? or does it just depend on what the problem asks?"

"I can't picture how the angles between forces and displacement correlate to what's going on. I don't know how to use the angles to see when work is negative."

"The idea of work is still a little confusing. I'm unsure of where this comes from or how we would measure it."

"Pretty much just kinematic energy as a whole, and why it's important. At this point, it seems like a whole bunch of formulaic substitutions that were made somewhat arbitrarily. I know that that's entirely not true, and that there’s plenty of usage. However, I need to figure out how and why."

"I think I just need to listen to the lecture in class to get a better understanding of it. No specific questions."

"I would benefit from an example in class of pushing an object with an acute angle/obtuse angle and whether it results in positive work or negative work."

"I'm sure there are somethings in there I don't know, we'll see."

Explain how the SI (Système International) unit for work is related to the SI unit for force.

"Force × distance = work, which is newtons (N) × meters (m) = joules (J)."

"the SI unit for work is the Joule while the SI unit for force is newton. The joule for work is found by the force multiplied by the displacement of the force on an object."

"Force can be put upon an object, but it isn't work until it moves. Therefore the unit for work has to account for movement."

"Because you need force to calculate the work."

"They both have to do with the newton."

Match the description of the work exerted by these forces for each object. (Only correct responses shown.)

Pushing in the same direction of motion: work done "on" the object (positive work). [87%]
Pushing opposite the direction of motion: work done "against" the object (negative work). [93%]
Pushing 90° sideways to the direction of motion: no work done. [47%]
Pulling such that the angle between the force and motion is an acute angle (between 0° and 90°): work done "on" the object (positive work). [64%]
Pulling such that the angle between the force and motion is an obtuse angle (between 90° and 180°): work done "against" the object (negative work). [60%]

For the catapulted squirrel, the bungee cord force does work __________ the squirrel, which __________ the squirrel's translational kinetic energy.

on; increases.	**************************************** [40]
against; decreases.	**** [4]
(Unsure/lost/guessing/help!)	* [1]

For the braking car, the brakes do work __________ the car, which __________ the car's translational kinetic energy.

on; increases.	****** [6]
against; decreases.	*************************************** [39]
(Unsure/lost/guessing/help!)	[0]

For Mrs. P-dog being catapulted, the bungee cords do work __________ Mrs. P-dog, while the weight force does work __________ Mrs. P-dog.

on; on.	** [2]
on; against.	********************************* [33]
against; on.	******** [8]
against; against.	[0]
(Unsure/lost/guessing/help!)	** [2]

For Mrs. P-dog's translational kinetic energy to be increased while being catapulted, the amount of work from the bungee cords must be __________ the amount of work from the weight force.

less than.	* [1]
the same as.	**** [4]
greater than.	************************************** [38]
(Not enough information is given.)	[0]
(Unsure/lost/guessing/help!)	** [2]

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

"Can we go over how angles change work?"

"Please go over these in class! Thank you."

"I guessed on most of the questions because I need help :("

"Will we be getting a lot of things like, 'this is how the work works,' or any other things like that?" (It will be more like, "this is how energy conservation works." Work and kinetic energy will be just components of energy conservation.)

"I would like a brief discussion of how the signs work. More closely the (+)=(+) or (-)=(-), is this every time or is there specific situations this isn't always true?" (The signs on both sides of an equal sign must have the same ± sign; otherwise it's not an equal sign.)

"How can you change an object's translational energy if it is infinitely small on Earth?" (With other infinitely small objects. Like us.)

"Why is kinetic energy important?" (...asked the dinosaur just before Earth was hit by the Chicxulub impactor.)

Online reading assignment: energy conservation

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 a presentation on energy conservation.


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 work equation helps a lot when calculating forces and makes a lot of sense as long as you are able to break down which numbers you are supposed to plug into each variable in the equation."

"That an object has higher potential energy when it is at a higher elevation. That there are two types of forces, conservative and non-conservative. For non-conservative force this relates to energy that cannot be regained, like energy loss due to friction on an object."

"Gravitational potential energy will increase the higher the object is because the formula for this is mass times gravity times height. So the higher an object is and more it’s fighting with gravity thus the more potential gravitational energy. Mechanical energy is the sum of potential and kinetic energy."

"Weight force of Earth on an object is a conservative force, does work AGAINST an object, removes energy, is able to store the energy, and return it to the object by later doing work on the object. Work against an object removes energy. kg·m²/s² = joules."

"What made sense to me from the presentation preview was the two conservative energies and how work done by those two forces can be stored or later removed without loss. With respect to gravitational potential energy, I understood that an object higher in elevation had more potential energy than an object on the ground."

"It's more important to look for the change of an energy rather than just the energy."

"It seems easier to work out the equations using the final minus initial method."

"Gravitational potential energy and the change in gravitational potential energy. I also understood balancing equations which is kind of similar like in chemistry."

"There are two (so far) types of 'stored' energy, elastic and gravitational. in an ideal environment, energy is 'conserved' because it is not lost in work (done by non-conservative forces)."

"A conservative force is one that doesn't matter the path of the object it would still end up in the same place with the same amount of work."

"Conservative forces are those that are exerted on or against and objects, removing its energy and storing it for use to do work on the object at a later time, unlike non-conservative forces where the energy against an object is lost or irreversibly converted to non-mechanical forms."

"I think I understand the difference between conservative and non-conservative forces pretty well. Conservative forces can be retained and returned, for example, if someone were jumping on a trampoline, when they come down for a jump, the trampoline acts against the person and slows them down to a stop, but that energy that was working against the person is later returned as the trampoline pushes the person back up into the air and the energy lost is returned."

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 found the work-energy theorem kind of confusing and would just need some more practice problems on them to fully understand it. We got a brief introduction to it last class, but it didn't stick all too well."

"I don't understand how to calculate these different types of energies."

"I understood most of this content well, but I would like to work through some example problems."

"I understand this material pretty well."

"Elastic potential energy. I am just confused by the spring strength and the stretch/crunch terms."

"What I do not understand is how gravity is a conservative energy. Isn't it acting on an object all the time so how can it be conservative?"

"Honestly the algebra of rearranging the equations tripped me up for a good 20-25 minutes. Also the differences in equations for conservative versus non-conservative forces."

"I found it difficult understanding what conservative and non-conservative forces mean; (I'm not sure if what I understand is correct)."

"Whether friction would be a conservative force or not."

"I was a little confused when I first read that an object has zero gravitational potential energy when it is on the ground and at higher elevations it has more and more. I was thinking of it backwards and now understand."

For the woman moving upwards after being catapulted, her translational kinetic energy __________ while her gravitational potential energy __________.

decreases; increases.	******************************** [32]
increases; decreases.	****** [6]
(Unsure/lost/guessing/help!)	*** [3]

For the ball bearing being launched by the slingshot, its translational kinetic energy __________ while the elastic potential energy of the slingshot bands __________.

decreases; increases.	******* [7]
increases; decreases.	***************************** [29]
(Unsure/lost/guessing/help!)	***** [5]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, indicate the changes in each her of energy forms. (Only correct responses shown.)

Translational kinetic energy: increases. [54%]
Gravitational potential energy: decreases. [68%]
Elastic potential energy (of the bungee cords): increases. [73%]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, the energy form that experienced the greatest amount of change (increase or decrease) was:

her translational kinetic energy.	****** [6]
her gravitational potential energy.	************* [13]
the elastic potential energy of the bungee cords.	*********** [11]
(Unsure/lost/guessing/help!)	*********** [11]

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

"The cat in the 'curling cat' video is amazing!"

"This last question of which force experienced the greatest amount of change for the woman falling off the building with bungee, shouldn't all three energy forms be experiencing the same amount of change? Or does the gravitational potential energy experience the greatest amount of change?" (Generally it is possible for three energy terms in the transfer-balance equation to experience the same amount of change (say, all increase the same amount, or all decrease the same amount), but only if there is a corresponding amount of work done on, or work done against the system. However for the woman falling off the building attached to the bungee cord, where we could assume that there is no work done by non-conservative forces, then the changes in all three energy terms (increases and decreases) must add up to zero, and so it won't be possible for all three of them to have the same amount of change, as there would need to be one decreasing energy and two increasing energies; or two decreasing energies and one increasing energy.)

"For the example with the bungee jumping women, the elastic potential energy decrease because it had its highest amount of potential energy when she was on top of the building and the gravitational potential energy decreased as she swings through the arc?" (Yes, as both the translational kinetic energy and elastic potential energy increase. Assuming that there is no work done by non-conservative forces, then the decrease in gravitational potential "feeds" the increases in translational kinetic energy and elastic potential energy.)

"I would benefit from some clarification of these examples of increasing and decreasing forms of energy."

"How to plug in information for the equations?"

"I need more time to read this section."

"If the two sliding boxes of equal mass/initial sliding speed slide across two different horizontal floor surfaces and come to a complete stop would have the same amount of work done on it by kinetic friction considering no changes in gravitational potential energy and elastic potential energy. But how is it that one box would travel farther, while the other box traveled less? Wouldn't there have to be some other force acting against the box that had the shorter sliding distance?" (No other horizontal force acts against these boxes other than the kinetic friction force. Both boxes have the same amount of work done against their motion by the kinetic friction force, but since work is force times displacement, the box that has the shortest sliding displacement must have a bigger kinetic friction force acting on it, and vice versa.)

Online reading assignment: work and energy

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 a presentation on work and energy.


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.

"Kinetic energy and the intial-to-final change in kinetic energy. I also understood the unit of joules and how kg·m²/s² translates to joules."

"The relationship between work and force and about the translational kinetic energy. I know that some forces go against force to decrease the kinetic energy and some forces go on it to increase kinetic energy."

"That an object that is stationary has no translational kinetic energy, but the faster an object moves the higher the value of joules. When work has a positive sign then that means that the force exerted ON (in the same direction) the object worked and the energy will increase, thus the change in energy will be (+). If the work is AGAINST (against is direction) the object then the resulting change in energy will be (–)."

"If the displacement is zero than there is no work being produced because work = force times displacement, and if the displacement is zero than the answer is going to be zero. Also the force has to have some component along in the direction as the displacement or else once again there is no work being done on or against the object."

"If a object doesn't move when force is applied to it, it hasn't done any work."

"The relationship that work and kinetic energy have with each other. When work is being done on an object, the kinetic energy increases because the objects movement increases. When work is being done against an object, the kinetic energy decreases because the object slows down."

"In the transfer-change equation, both sides of the equation have to have the same sign."

"Work is equal to a relationship of force (at a given angle) times the displacement the object moves. If there is no displacement, there is no work."

"To be fully honest this chapter is very confusing 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.

"I don't really understand what is meant by tail-to-tail angle and why it is important when we measure work done on or against an object."

"Connecting all of the components of the work-energy theorem."

"I was a little confused about what translational kinetic energy is. I was also a little confused about the calculation of work."

"I kind of understood the work part of the reading. I need to see some more examples of calculating work done in class."

"The cosθ part of W = (Fcosθ)·s confuses me. What do you mean by 'tail-to-tail?'"

"I would like to do a few example problems just to get comfortable."

"I found the majority of the 'work' concepts to be hard for me to grasp. For some reason it really confuses me and I may need a decent amount of explanation to understand the concept."

"Everything makes sense."

Explain how the SI (Système International) unit for work is related to the SI unit for force.

"The unit is joules which is the product of the force and displacement."

"The joule is the SI unit for work and is defined as newton·meters."

"Force is in newtons while work is in joules but, work equals newton times meters, that is, force times distance."

"Both in newtons?"

"Both in joules?"

Match the description of the work exerted by these forces for each object. (Only correct responses shown.)

Pushing in the same direction of motion: work done "on" the object (positive work). [96%]
Pushing opposite the direction of motion: work done "against" the object (negative work). [94%]
Pushing 90° sideways to the direction of motion: no work done. [65%]
Pulling such that the angle between the force and motion is an acute angle (between 0° and 90°): work done "on" the object (positive work). [38%]
Pulling such that the angle between the force and motion is an obtuse angle (between 90° and 180°): work done "against" the object (negative work). [40%]

For the catapulted squirrel, the bungee cord force does work __________ the squirrel, which __________ the squirrel's translational kinetic energy.

on; increases.	********************************************** [46]
against; decreases.	* [1]
(Unsure/lost/guessing/help!)	* [1]

For the braking car, the brakes do work __________ the car, which __________ the car's translational kinetic energy.

on; increases.	** [2]
against; decreases.	********************************************** [46]
(Unsure/lost/guessing/help!)	[0]

For Mrs. P-dog being catapulted, the bungee cords do work __________ Mrs. P-dog, while the weight force does work __________ Mrs. P-dog.

on; on.	*** [3]
on; against.	**************************************** [40]
against; on.	** [2]
against; against.	[0]
(Unsure/lost/guessing/help!)	*** [3]

For Mrs. P-dog's translational kinetic energy to be increased while being catapulted, the amount of work from the bungee cords must be __________ the amount of work from the weight force.

less than.	** [2]
the same as.	*** [3]
greater than.	*************************************** [39]
(Not enough information is given.)	[0]
(Unsure/lost/guessing/help!)	**** [4]

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

"I was having a little trouble with figuring out why the magnitude of normal force of a hill on the truck (that's on top of a hill) is less than the normal force truck going through a dip." (The net force (for uniform circular motion) on the truck on top of the hill must point downwards (towards the center of curvature), while the net force (for uniform circular motion) on the truck going through the dip must point upwards (again, towards the center of curvature). Since the (downwards) weight force on the the truck in both cases is the same (it must be!), then the only thing that can be different is the amount of (upwards) normal force on the truck in each case.)

"I think I understand this material so I'm looking forward to doing some problems in class and a little clarification."

"I find the work-energy theorem confusing because if the work can either be done on or against the object, how do you do work 'against' something? Also, how is it that the left-hand and right-hand sides of the equation can have the same sign?" (A force can do work "against" the motion of an object if the force is directed in the opposite direction of its motion, which would slow it down. Also the left-hand side and right-hand side of any equation must be equal to each other (that's why it's an "equation," right?), so they have to have the same value and the same positive or negative sign.)

"I am honestly lost." (I will honestly try to un-lost you, as long as you let me know specifically what you're lost on.)

"Can you let me know the concepts I need to know for the midterm?" (The study guide is already posted, click on the "Review" link next week on the course calendar.)

"I just wanted to say that I am afraid of the upcoming quiz because I don't feel adequately prepared. If the quizzes test students' mastery of the mere basics, and if a student gets one or two questions wrong, does that mean that they won't succeed on the midterm? How can they succeed on the midterm if they are struggling with the basics?" (The quizzes are meant to get you to keep up with the basics so you don't get stuck studying for the more complex topics on the midterm. Even if you don't do as well as you would like on the quizzes (and getting only one or two questions wrong on a quiz is not that bad; cf. the grading cut-offs for this course), there should be enough time after a quiz and before the midterm for you to build upon your understanding of the material from basic to more complex understanding.)

"Does friction force take into account the surfaces of the materials? For instance, would slick granite be different from shaggy carpet for an object to slide on?" (Yes, and the study of how the types of surfaces affect friction is called tribology.)

"Would the thickness of the string influence the amount of tension? For example, if the string is thicker would the tension be less?" (The amount of tension in a string (whether thin or thick) will vary on the situation; specifically how little or how much you pull on it. However, the maximum amount that you can pull on a string before it breaks does matter on whether it is thin or thick (assuming that they are both made from the same material).)

"Can you review the general rule in lab to determine if a measurement can be done once or several times? Say different values for a certain measurement vary more than twice the value of the uncertainty--does that mean our group should take more measurements and record them, then take the average of all these measurements?" (Yes, as time allows. Otherwise three to five repeated measurements is sufficient.)

"How long did it take to get good at doodling?" (Practice, practice, practice. Anyone can doodle. Also, did you know that I drew an online comic strip nearly 20 years ago?)

Online reading assignment: energy conservation

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 a presentation on energy conservation.


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.

"Conservative forces do work that can store and later retrieve energy without loss, and nonconservative forces do work that irreversibly loses or gains energy."

"Gravitational potential energy and elastic potential energy and translational kinetic energy are all related. Together they make up the right side of the transfer/balance equation."

"The idea of stored energy somehow makes sense to me. Taking a couple of science classes where we learned about the stored energy in ATP and how it is spring loaded in a way."

"Kinetic energy is energy in motion. Potential energy is stored energy. Potential energy is most commonly determined by the change in height. Since gravity and mass stay constant, height is the most important determinant in change."

"I understand that there are conservative forces, such as gravitational weight and elasticity, that conserve energy by storing it in the system and then applying work to release the stored energy. Conversely, frictional and dragging forces are non-conservative, and energy is lost."

"Conservative forces are forces that store energy for later use. An example of this is the weight force of Earth on an object. Potential energy is that energy that changes position to be stored for later."

"Elastic potential energy is energy stored as a result of applying a force to deform an elastic object. The energy is stored until the force is removed and the object springs back to its original shape, doing work in the process."

"The complete form of the total energy conservation equation shows the full transfers between kinetic energy, along with potential elastic and gravitational energy. They all individually can be increasing or decreasing, but they all must result in the non-conservative work term."

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 whole concept of non-conservative forces and conservative forces was confusing to me. It took me multiple readings of most of the passages in the online presentation just to get the gist of it. I understand it a little more now but it is still very confusing to me."

"I'm not exactly sure on this but when an object is in motion does it still posses potential energy or is there no potential energy and it has all been converted ot kinetic energy? can it posses potential elastic energy but still have no potential gravitational energy?"

"I'm struggling with the use of the equations for the energy types."

"I do not completely understand conservative force and its two types. Also I did not understand the gravitational potential energy equation."

"I don't understand exactly how to apply mechanical energy and know when it is conserved or when it isn't."

"Most everything in this chapter, starting from conservative and non-conservative energies, to elastic potential energy and the transfer/balance equation."

"Nothing was found too confusing."

"All I really understood this from reading assignment was how the work-energy theorem is used, and I;m still not 100% okay with how to apply it."

"Nothing was found too confusing."

"I feel like I understood this portion pretty well in that I feel confident with my answers to the reading assignment."

For the woman moving upwards after being catapulted, her translational kinetic energy __________ while her gravitational potential energy __________.

decreases; increases.	********************************* [33]
increases; decreases.	***** [5]
(Unsure/lost/guessing/help!)	** [2]

For the ball bearing being launched by the slingshot, its translational kinetic energy __________ while the elastic potential energy of the slingshot bands __________.

decreases; increases.	*** [3]
increases; decreases.	********************************** [34]
(Unsure/lost/guessing/help!)	*** [3]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, indicate the changes in each her of energy forms. (Only correct responses shown.)

Translational kinetic energy: increases. [78%]
Gravitational potential energy: decreases. [70%]
Elastic potential energy (of the bungee cords): increases. [55%]

For the woman falling off the building starting from the edge of the roof to just before reaching her lowest point of descent, the energy form that experienced the greatest amount of change (increase or decrease) was:

her translational kinetic energy.	******* [12]
her gravitational potential energy.	**************** [16]
the elastic potential energy of the bungee cords.	******* [7]
(Unsure/lost/guessing/help!)	***** [5]

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

"If I could ask you to go over one thing in the next lecture, it would be bungee-swinging woman. Thanks!"

"The last example got me, not as comfortable with horizontal motion being mixed in with vertical motion and determining which force is greatest."

"Go over conservative forces?"

"I would like some extra discussion explaining the different forces and energies. It just seems like maybe a little much at the moment."

"Please go over this stuff."

"Could you explain a little bit more on elastic potential energy?"

"Very wordy reading assignment, read it over a few times and still can't understand it completely."

"Those equations hurt my eyes."

"Do we have to remember all of these equations?" (No, all the energy equations will be given to you, in the same format as the last page of the worksheet packet.)

"Would any object that has the potential to fall have potential energy? Does this work for objects that never actually do fall?" (Yes; but if they never fall their gravitational potential energy will just remain constant--it's like having a gift card ("potential money?"), but never getting around to use it.)

"I’m really sorry I haven’t been able to get to some assignments! I’m trying to balance everything better in my life, I hope you understand." (Just letting me know what kind of crazy is going on with your outside-of-physics life is still informative to me, and you still get completion credit for stuff like this.)

"I'm enjoying the class!"

Online reading assignment: work and energy

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 a presentation on work and energy.


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.

"Translational kinetic energy is the energy of motion, it is dependent on the objects mass and the square of its velocity. Work done on the object will result in an increased change of change in transitional kinetic energy, while work done against the object will decrease it."

"Translational kinetic energy is the energy of motion. To change the translational kinetic energy of an object, a force must do a certain amount of work either on, or against the motion of the object. Work on an object increases the speed by the work against the object decreases speed."

"Work is the force that is applied to an object multiplied by the distance/displacement it traveled."

"I understand the concept of work and that to do work on or against something that a force must be applied."

"Kinetic energy is energy in motion compared to potential energy which is not moving."

"When the force is in the same direction as the displacement work is positive. The opposite is also true when the force is in the opposite direction as displacement then work is negative."

"When a force performs work on an object, there will always be a change in kinetic energy."

"A stationary object has no translational kinetic energy, and the faster an object moves, the more translational kinetic energy it has. Also, if a force does work on an object, then the work will have a positive sign, and the translational kinetic energy of the object will increase."

"The SI units I understood quite well."

"I understand the meaning of work and how it is used in the real world, just not exactly how to calculate angles and directions."

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 kind of confused about how the angles and the cosθ that was thrown in there."

"The squirrel catapult part with the 90° angle thing is the only part of the reading that I found confusing."

"I'm a little confused on the work = F·scosθ equation."

"I didn't find any main concepts confusing, but a little review in class would be helpful. Just clarifying application to real-life circumstances like what was done in the online presentation would be helpful."

"The concept of joule was a little confusing. As well as the kinetic energy section. I understand the general idea, but a little more practice and explanation would help."

"Applying the work-energy theorem."

"The examples and proofs in the book confused me, as they tend to. I am somewhat confused by the angle relating to force and how that is applied to the kinetic energy equations."

"I don't understand translational kinetic energy, the work energy-theorem and how I would begin to apply these to problems."

"All of it. So far so good. This section is pretty easy to understand."

"Nothing too hard nor confusing was found."

"Most of the stuff I read was pretty clear."

Explain how the SI (Système International) unit for work is related to the SI unit for force.

"Work is related to force by way of newtons (the SI unit of force), and when you multiply them by meters, the joule (unit of energy) is found."

"A joule is the work done by a force of one newton acting to move an object a distance of one meter in the direction in which the force is applied."

"I'm confused by this question."

Match the description of the work exerted by these forces for each object. (Only correct responses shown.)

Pushing in the same direction of motion: work done "on" the object (positive work). [81%]
Pushing opposite the direction of motion: work done "against" the object (negative work). [92%]
Pushing 90° sideways to the direction of motion: no work done. [46%]
Pulling such that the angle between the force and motion is an acute angle (between 0° and 90°): work done "on" the object (positive work). [54%]
Pulling such that the angle between the force and motion is an obtuse angle (between 90° and 180°): work done "against" the object (negative work). [54%]

For the catapulted squirrel, the bungee cord force does work __________ the squirrel, which __________ the squirrel's translational kinetic energy.

on; increases.	***************************************** [41]
against; decreases.	***** [5]
(Unsure/lost/guessing/help!)	** [2]

For the braking car, the brakes do work __________ the car, which __________ the car's translational kinetic energy.

on; increases.	*** [3]
against; decreases.	****************************************** [42]
(Unsure/lost/guessing/help!)	*** [3]

For Mrs. P-dog being catapulted, the bungee cords do work __________ Mrs. P-dog, while the weight force does work __________ Mrs. P-dog.

on; on.	******** [8]
on; against.	******************************** [32]
against; on.	*** [3]
against; against.	** [2]
(Unsure/lost/guessing/help!)	*** [3]

For Mrs. P-dog's translational kinetic energy to be increased while being catapulted, the amount of work from the bungee cords must be __________ the amount of work from the weight force.

less than.	** [2]
the same as.	**** [4]
greater than.	*************************************** [39]
(Not enough information is given.)	[0]
(Unsure/lost/guessing/help!)	*** [3]

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

"Is 9.80 m/s² the same as in 'g's?' Otherwise, everything is pretty straightforward." Yes, if you measure acceleration (or weight) in g's, then that's how many times this acceleration (or weight) is greater than that due to gravity."

"I need more explanation on connecting force and motion."

"I was confused by the work-energy theorem. I would appreciate some review of that as well as work in general."

"This all makes sense, but in a scarily easy way where I'm pretty sure I am completely wrong."

"The example questions did not click to me. I do not understand the difference of work and force."

"I feel I'm tackling the major concepts of the class at home, while not fully understanding most of them, and then coming into class and just brushing the surface of these concepts with some problems but little explanation and/or direction on how to go about solving these problems."

"Work on an object makes sense, but again it becomes a problem of integrating what I currently know into what is new information. Hopefully in-class work will aid in my understanding."

"I would like to work example questions in class."

"I think I understand most of the material but could benefit from more examples of how work effects transitional kinetic energy in different situations. Additionally some review on the changing of the angle of the force and displacement vector and how it effects the work being done on an object."

"The bungee cord question was the most confusing for me out of all the questions. Very quickly, if there is time, I would like you to clarify the answer to this question in class tomorrow. Thanks."

"I really am starting to understand physics better now than I have before."

"Nothing really confusing; I just wish you could teach this instead of trying to teach myself."(Well, I'm okay with lecturing in class as long as I know specifically what you need to hear; or if you're not too confused, then I can build upon what you already know. But I have to have to you try to go through this material for yourself first (which can be frustrating!), at least to familiarize yourself with the new definitions and concepts before we talk about them in class.)

"The increased description during the presentation preview increased my clarity on the topics. If possible can you keep that level of explanation or even increase it?" (I think when there are plenty of applications at the end of some presentations, I can try to break down one application as an extended example for you while leaving the rest for you to do on the reading assignments.)

"Why is it that there would be no work done on an object at 90° sideways to the motion?" (Forces exerted perpendicular to the direction of motion would not affect its speed, but would only deflect the direction of its motion. So, basically uniform circular motion, where the speed remains constant while the direction continuously changes, due to the net force in the centripetal direction, sideways to the velocity vector.)

"Is it possible to have a force that is doing both, working on and against an object?" (No, either a force points along the direction of motion, or opposite the direction of motion, or sideways. If the force is diagonal to the direction of motion, then you can break it down into components parallel to and perpendicular to the direction of motion.)

"Relating back to vectors, if the angle between force and displacement were to be past 90°, would the angle be taken from the +x-axis in the counter clockwise direction?" (Yes, because force and displacement, when drawn "tail-to-tail," would make an obtuse (greater than 90°) angle.)

"More of a concept question but why would it always be cos rather than say sin or tan to calculate work?" (If displacement is set along the +x-axis, then you use cosine because you are basically finding the (horizontal) component of force "along" the direction of motion.)

"If an object is moving to the right, then would gravity have no effect on its kinetic energy because gravity is 90° straight down?" (Yes.)

"Can work being done on a object if it's stationary? Or would it be against it?" (Work has force and displacement in it, so while a force can be exerted on an object that is stationary, the displacement (straight-line vector from start-to-finish) would be zero, so work be zero as well.)

"Are the midterms set up the same as the quizzes are?" (No; see comment below.)

"In the midterm do you ask questions like above and like those found in the blog? and also definitions? Or will it be essentially solving problems?" (The midterm will have four questions where you have to apply concepts in your explanations; there will only be one problem where you need to strictly use equations to calculate stuff.)