Below is the teacher guide for those of you wanting to try this lesson out for yourselves. It describes how I edited the audio file and detailed instructions for each demonstration. I also suggest you watch the YouTube video. It will help with the parts that involve notes and example problems. At the bottom are sources for the audio file, the Feynman Lectures on Physics book, and the student note guide.
1. Starting on page 4-2, I edited out most of section 4-2, Gravitational Potential Energy. The cut starts just after he says “I wish to discuss the formula… near the surface of the earth”. I pick up the lecture again at the start of the second paragraph on page 4-4 where he says “We call the sum of the weights times the heights gravitational potential energy”. Although the deleted section is intriguing, it would be hard to follow unless you actually constructed or animated a machine like the one described. I think you would have to either deliver this part of the lecture yourself or repeatedly pause the tape.
2. The second edit starts with the second paragraph on page 4-7. The edit starts after he says “it is E = mc2” and picks up again at the start of the very last paragraph on page 4-8 where he says “Finally, we remark on the question”. This paragraph is the very end of the lecture. This edit is primarily for time constraints and could easily be included if you want a longer lecture.
Assisting: As the lecture plays, I perform many tasks to assist with it. These tasks include operating demonstrations, writing out equations and notes on the board, and showing and doing calculations on prepared transparencies of figures from the text. With some practice you can coordinate your actions with what Feynman is doing with several eerie results. He will even refer to you directly at one point. Although I might get a little carried away with these tasks, I have been doing this for many years and have added demonstrations as I have guessed at what is actually being done during the lecture. I also believe the more you do the more attention the students will pay to the lecture. Each task I perform is described below.
1. Introduction: I give a brief history of Feynman’s career as if he is really there to speak and I am introducing him. When I turn it over to him, I trigger a light by remote control which signals an unseen helper to open and close the door as if Feynman is walking in. I shake his hand and start the lecture.
2. Toy Blocks: I bring in a set (you don’t need 28) of blocks and play with them to go along with the description in the lecture. I have a rug to hide one under, a window to throw them out of, a toy box, and a tub of “dirty water” (food coloring). I write equations 4.1 and 4.2 on the board as Feynman describes them. I erase the “number of blocks seen” when he states that there are no blocks.
3. List of Different Forms of Energy: On the board I have written this list as given in paragraph on page 4-2. However, in the lecture he realizes he has left out elastic energy. I leave it out on my list and quickly add it when he mentions that he left it out.
4. Equations 4.3 and 4.4: I write these equations on the board and add a few things like the symbol we use for gravitational potential energy, Ug.
5. 3-4-5 Incline Plane: I set up one of these using a dynamic cart and track like the one shown in figure 4-3. I label the distances and the masses to show the 3-4-5 relationship. I show how the cart will remain stationary at any point on the track. I then move to the overhead and show figure 4-3. I help him explain that the 1 lb. weight only rises 3 feet while the other weight lowers 5 feet using an overhead pen.
6. Epitaph of Stevinus: I help Feynman out using a transparency of figure 4-4 by showing how the lower seven balls are balanced leaving the 3 on the left balanced by the 5 on the right.
7. Screw Jack: A transparency of figure 4-5 and an overhead view of the jack showing how Feynman arrives at a distance of 1260 inches will help the students see this application of Work = Force ´ Distance.
8. Weighted Rod: A transparency of figure 4-6 will help you illustrate this simple example of the principle of virtual work. Although this is usually not done in a high school class, it is a good example of some of the powerful energy methods that they will learn later in college. When you solve for the unknown weight, Feynman will actually refer to you and comment on your mathematical skills. I believe he is really just referring to himself in the third person, but the effect is eerie.
9. Large Pendulum: Set up a large, heavy pendulum to use while Feynman starts section 4-3, Kinetic Energy. I use a bowling ball. At the beginning of the second paragraph he says “We must get the formula…” This is where he does the stunt where he holds the heavy pendulum to his nose, releases it, and lets it swing back, confident it will not hit him on the return swing. If you practice you can time it so events in the classroom match events on the tape. Listen for his chair scraping as he gets ready to release the pendulum. Sometimes my class will applaud along with the Caltech students.
10. Small Pendulum: This part is not in the text. I believe that Feynman is demonstrating that a pendulum will return to the same height even if the string hits a bar at the lowest part of the swing, similar to the “Cut Short” lab in the Conceptual Physics lab manual. He then lowers the bar so the pendulum wraps around the bar and he gets a few laughs, you will too.
11. Derivation of Equation 4.6: I add to this on the board by deriving the height of a vertically launched projectile using kinematics. I also put this equation in a more familiar form by setting W = mg.
12. Elastic Energy: As Feynman starts section 4-4, Other Forms of Energy, I use a vertical spring mass to animate his comments about elastic energy. As he discusses heat energy, I use a dynamic cart on a track with a spring on either side. You can touch the track and pretend that it is hot when he says that things get warmer. In the lecture he notices the mass hanging on the spring starts to twist. I stop mine from moving vertically and show this twisting oscillation to prepare them for torsion pendulums later in the year.
13. Forms of Energy: I use the list described in number 3 above to show the connections Feynman makes between the different forms of energy and write E = mc2 to help with the mass energy explanation.
14. Finish: I let Feynman finish up on his own with the last paragraph. You may even get a round of applause at the end as he does from the Caltech students. I then take questions from the students and show them my Feynman book collection. I find myself referring to many things done in this lecture as we proceed through the energy unit (especially the toy blocks). I find this day to be time well spent but a little exhausting trying to keep up with the master.
Notes about the large pendulum: This is a common physics demonstration and can be done safely. I was fortunate to always find a sturdy attachment point on the ceiling of my classroom. If I moved to a new classroom, I would remove a few ceiling tiles and look for something suitable. If you are unsure, go to your maintenance crew manager and ask for help. Show a video of the demonstration, like the one below, to get them on your side. It doesn’t need to go all the way to the floor. It is important to know that the tension in the rope is greater than the weight of the bowling ball. In fact, if released with the string in a horizontal position, the tension in the rope is 3 times the weight at the bottom. Bowling balls can often be obtained from local bowling alleys for free. Just tell them what you want it for and they are usually happy to help out. I do not recommend letting students do it. If a student asked, I told them to come in after class to try. If they showed up (many wouldn’t), I had them stand so that they were leaning against my front table. This gives a reference to help avoid moving after you release the ball. After a discussion about why pushing the ball would be bad, I had them gently hold the ball from the sides just in front of their nose. I watched carefully to make sure they did not lean forward after releasing it. I never had an accident with this demonstration. However, that is similar to NASA’s reasoning after noticing another large piece of external tank insulation hit the Space Shuttle Columbia. Here is a video of a teacher that did not follow my advice.
References and Resources:
1. For the Six Easy Pieces CDs: search “Six Easy Pieces Feynman with CD” for several sources. It is $11.99 for the audiobook download at audible.com It is also included in “The Feynman Lectures on Physics: Volume 5, Energy and Motion on audible.com
2. The Feynman Lectures on Physics, Volume I, Feynman, Leighton, Sands, Chapter 4. Now available free online at: http://www.feynmanlectures.caltech.edu/
3. I hand out this work sheet to make it easier for students to take notes.