Practical Uses of Gravitational Potential Energy

The summer class just covered gravitational potential energy (GPE) and it’s fun to think of ways that GPE is pragmatically useful. Hydroelectric power is in part a way to harness GPE by taking a mass of water that is higher up (behind a dam) and then, in a controlled way, releasing GPE by allowing the water through to lower elevations.

GPE is also being explored as a store of energy when wind and solar energy exceed demand. You see, wind and solar power often go beyond what people need at certain times during a day, and then they end up supplying too little at other times of day (i.e. solar doesn’t produce energy at night). One obvious approach is to develop battery technology that can soak up the excess energy production and then release it back to the energy grid when other power sources are undersupplying. The problem is that we don’t know how to make batteries dense and efficient enough to solve the problem, so people are exploring alternatives, one of which is to use the extra energy to lift very heavy weights high up in the air, which can then be lowered in a manner that causes a generator to turn, thus siphoning off (some of) the GPE back into electrical power. Here’s an article describing some recent work on this:

Hello Summer Class of 2022!

I’m excited to start our summer course on mechanics!

Summer session is a whirlwind as we pack a full semester of physics into approximately 5 weeks. Our class will function mainly in a traditional manner, but I learned a couple of things from teaching during COVID that I intend to continue to incorporate into how the class will work. Among these are recordings of all of our meetings, easy access to slides and notes, and some Zoom-based components of the course that I used to run face-to-face but are much easier to do remotely.

Please take a look at the syllabus, which is linked to on the sidebar of this site.

You can find some basic information (my contact info and the lab TA information) by clicking on the “Welcome!” link on the upper-right or following the link below:

Some Studying Resources

I have posted a couple of resources that may help in studying for the energy quiz.
  1. I’ve posted links to some review videos and an office hour review of the energy concepts and some quantitative methods. You can find the links on the lecture schedule on the date of the energy quiz.
  2. I also have some links to example and hint videos that can be accessed via the course website. Click on the sidebar link to “Example Videos”.

Quiz Postponed to Monday 2/28

Due to the campus staying closed until 10 am tomorrow (2/25) we will postpone the quiz until Monday (2/28).

To make up for lost time I will be posting some videos covering material I would have covered in lecture on Monday. I’ll send out an announcement when the videos are ready to be viewed.

Keep warm and stay safe! Enjoy the extra morning time.

Welcome To PHY 111/113, Spring 2022 Students!

Welcome to our Spring 2022 Classical Mechanics course.

You can find essential information by clicking on “Syllabus” and “Lecture Schedule” on the sidebar.

Feel free to email me with any questions you may have. You can find my contact info by clicking on the button at the upper-right of the site that says “Contact Info”.

Looking forward to seeing you in class!

Greetings Summer Class of 2021!

I’m excited to start our summer course on mechanics! And I’m extra excited to be able to do so in person!

The summer session is always a whirlwind as we pack a full semester of physics into an approximately 5 week period. I’m hoping to utilize some of the material developed for remote learning this past year to help you manage this time a bit more flexibly. We’ll begin our first session with some introduction to various components of the course as well as some discussion of how to make the course work best for you.

Please take a look at the syllabus, which is linked to on the sidebar of this site.

You can find some basic information (my contact info and the lab TA information) by clicking on the “Welcome!” link on the upper-right or following the link below:

Hello Spring 2021 PHY 111/113 Students!

Welcome to Classical Physics 1! The main focus of this course is the theory of classical mechanics that was first brought to mature form by Isaac Newton. I take a somewhat non-standard approach with a heavy emphasis on the concepts of momentum and energy, but at the end of the day, it’s all the normal stuff (forces, motion, baby Yoda…)

This site is the primary place to come for course resources. You’ll find links to the syllabus, the schedule, and the online homework system via the sidebar.

The course lecture schedule will gradually be populated with links for our Zoom sessions.

Note that for the online setting, I will divide the class into smaller groups of about 20 students each. These groups will normally meet once a week on a particular day (Monday, Wednesday, or Friday). The main lecture content is embedded with the online problem sets and our live meetings will be in the form of tutorials. These are a sort-of hybrid between lectures, recitations, and quiz sessions, sometimes they will be more of one, sometimes more of the other. The key to getting the most out of this course is to come prepared to the tutorial meetings. Typically this means that you have watched the lecture videos for that week and have attempted at least some of the problem set problems. Sometimes, there will be something different or extra that I assign to you. The smaller group size means that we will be able to be far more interactive, particularly in the online situation.

Please be on the look out for more information and don’t hesitate to email me if you have questions. My email is dkagan and the domain is

PHY 113 Announcements and Reminders for Wednesday, 6/17

​Good morning!
Some announcements and reminders for today:
Recommended schedule:
Lecture 6 (Momentum lecture 1) – done by yesterday
Lecture 7 (Momentum lecture 2) – done today
Lecture 8 (Energy lecture 1) – do tomorrow
Note:  will send out a message when lecture 8 is available.
Some of you have spotted code errors. I’ve tried to correct them. Please let me know if you run into more problems.
Upcoming Quiz
We will use the first 20 minutes of Friday’s tutorial for a quiz on topic 1 (kinematics). I will send out more information about the way the quiz will work tomorrow.
Score Reports
I’ve opened up a score report link on the course website. If you click on the link on the sidebar, you will go to a page that asks for your registered e-mail and your CAPA number. After clicking ‘submit’ a list of your scores for the various topics, the homework problems, and lab is displayed. At the moment, only the homework sets from the kinematics lectures have been uploaded and processed.

Hello Summer Class of 2020

Hello everyone!

I’m very excited to get our class going this summer. As you can see from the summer schedule, we are covering a normal semester’s worth of course material in the span of 5 weeks (less actually) so things will be intense! On top of that, we are doing this online. While I gained some experience running the last third of my course last semester, I expect that I have stuff to learn about the best way to run things.

Please take a few minutes to watch this introductory video to the course. It covers:

  • How to get in touch with me
  • How to find important course materials like lectures and problem sets
  • Pretty pictures!

Don’t miss the video underneath as well that delves a bit into the course’s main topics and some aspects of how I grade.

Course Introduction:

Course Topics and Some Aspects of Grading

PHY 111/113 Going Forward

I hope you are all keeping well, safe, and finding ways to have some fun during our extended spring break. As you are probably aware, our campus is going to run the rest of the semester’s courses online, which includes lectures, recitations, and labs.
I wanted to give you an idea of what to expect for phy 111 / 113.
FIRST: If you have not signed up for Campuswire, please do so now. If you cannot find your site invitation e-mail, check your junk folder or e-mail me. I will be posting announcements and reminders there, as well as on my course site, located at
For especially important announcements, I will also send out mass e-mails, but I will not do so for announcements involve homework and exams.


I am recording videos of all my lectures. These will display my slides with my voice going through the main points. As you know from lecture, the text of the slides does not always contain the full content of the lecture. My expectation is that you will watch the videos and take notes, just as you would in the ordinary class.
I will intersperse the slides with video of worked examples—similar to how I do these things on the doc-cam in class.
These lecture videos will be released during the days we would ordinarily have our lectures. I am exploring creating a private YouTube channel and posting the lecture videos there. The slides will be posted to the usual folders as they have been throughout the semester.
In place of the usual lectures I will hold virtual office hours via Zoom. I am still trying to work out the best way to schedule these hours so that every one of you has an opportunity to attend at least 2 – 2.5 hours per week. I will send out a poll and use that to help me schedule the times.


I am currently working with the TA’s on a plan for holding recitations at the usual scheduled times. I believe that these can be held as Zoom sessions, but we are currently sorting out the details.


The TA’s and I are working on adapting the labs so that they can be done remotely. Unfortunately, since I cannot be sure that all of you have the same ability to conduct actual experiments at your homes, the current plan is to produce videos that you will then analyze using video tracking software. Guided worksheets will be distributed and you will submit your results and the worksheets. Things may change, but I expect that the labs will go something like I’ve just described.


Homework will still be done via CAPA. That shouldn’t change very much.


My current plan (which could change!) is to release the exam on CAPA during our usual lecture period. The CAPA version of the exam will involve no data entry, but just display the questions. The idea is that you would work on the questions on fresh sheets of paper and then scan and submit your work at the end of the exam period using a private link to a shared folder. I will then manually grade the exams according to my usual system.
Assuming that the above idea is feasible, I will send you a link to a free phone scanner app (CamScanner), which you will use to scan your exam work as a single pdf file.
NOTE: Our upcoming exam is pushed back by one week. It was originally scheduled for 3/27, but will now be held on 4/3 (April 3rd). More information will be posted on the course site ( as well as on Campuswire.

***Other Possibilities***

I am open to suggestions from you. If I have extra time, and there is enough interest, I am happy to produce extra example videos.

***Parting Thoughts***

What we are all going through right now is unique and historic. All of us have to adapt to these strange circumstances. I want you to know that I am aware of the difficulties that the situation may impose on some of you and I fully intend to be as flexible as possible as we continue through the course. If you need any extra assistance, please do not hesitate to reach out to me to schedule a virtual appointment.
If you are anxious about grades or other aspects of the course, note that I have a lot of data from past semesters for how the grades typically turn out. If, after we complete the course, I notice that there is a big shift in the score distribution compared to past semesters, I will make adjustments that give you the benefit of the doubt.
The sudden need to rapidly shift the course to online delivery will mean that there are bugs, errors, and other problems. Please be as patient with me and the TA’s as you would hope that we will be of you. We’re all in this together.
Stay well, safe, and try to find ways to enjoy your extra break time. Please feel free to contact me if you have any comments, concerns, or questions,