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%]
on; increases. ********************************************** [46] against; decreases. * [1] (Unsure/lost/guessing/help!) * [1]
on; increases. ** [2] against; decreases. ********************************************** [46] (Unsure/lost/guessing/help!) [0]
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?)
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