Day 15: A Standard Unit for Energy

After yesterday's experiments, I decided we should have decided upon a standard unit for energy. In this case, a standard rubberband pulled back some distance stores 1 unit of energy. Need to test how much energy a cart has? Send it into a rubber and see how far it stretches.

I know this isn't perfect, but we aren't developing quantitative relationships now. Just trying to get at the factors which affect the amount of energy in moving carts and stretched rubberbands.

(A puck launcher is pictured here because I forgot to take a picture of my actual set up: two large colored rubberbands from Staples are looped together and stretched across the width of the lab table, secured with c-clamps. A puck launcher would make a nice portable energy measurer. )

Day 14: Energy Lab Results

Looks like we’ve got some work to do regarding: (1) Controlled experiments; (2) Conservation of energy ; (3) Writing scientific explanations in “claim-evidence-reasoning” format.

Day 13: Energy Experiments (Round 1)

College-prep students using carts and rubber bands to design their own qualitative energy experiments. The focus is "What factors determine the amount of energy stored in a moving cart? In a stretched rubber band?" In pre-lab, we brainstormed possible factors, then I assigned each group one cart factor and one rubber band factor to investigate (with some overlap among groups for consensus purposes).

I forgot how painful it can be watching students design their own experiments. I might even have them do it over again, but with more guidance from me.

(But that's OK, because now they'll be ready for the guidance, having experimented on their own first. Right? I'm thinking about Schwartz's "A Time for Telling.")

Day 12: Feynman’s Lecture on Conservation of Energy

Today in college-prep physics we wrapped up our discussion of energy with Richard Feynman’s lecture on the conservation of energy. Before doing so, I gave some background about Feynman, including the intersection of art and physics in Edward Tufte’s new exhibition “All Possible Photons: The Conceptual and Cognitive Art of Feynman Diagrams.”

 

I also mentioned the irony of Feynman’s brilliant lectures and his perception of their failure. From the Preface of Six Easy Pieces (and also the Preface of The Feynman Lectures of Physics):

I don’t think I did very well by the students. When I look at the way the majority of the students handled the problems on the examinations, I think that the system is a failure.

…

I think, however, that there isn’t any solution to this problem of education other than to realize that the best teaching can be done only when there is a direct individual relationship between a student and a good teacher—a situation in which the student discusses the ideas, thinks about the things, and talks about the things. It’s impossible to learn very much by simply sitting in a lecture, or even by simply doing problems that are assigned. But in our modem times we have so many students to teach that we have to try to ???nd some substitute for the ideal. Perhaps my lectures can make some contribution. Perhaps in some small place where there are individual teachers and students, they may get some inspiration or some ideas from the lectures. Perhaps they will have fun thinking them through—or going on to develop some of the ideas further.

RICHARD P. FEYNMAN
June 1963

We listened to an audio recording of Feynman’s toy block analogy for the conservation of energy.

I also provided students with a text copy of the lecture and some follow -up questions: 03_U5_ws1_Feynman_Lecture

(NOTE: While researching links for Feynman and Tufte, I came across an article on The Feynman-Tufte Principle … A visual display of data should be simple enough to fit on the side of a van. An nice, short read.)

Day 11: More Energy Transfers

“On a group whiteboard, draw an Energy vs. Time graph for the cart
hitting the rubberband. Include:
(1) A graph for Ecart
(2) A graph for Erubberband
(3) A graph for Ecart + Erubberband

Start your graph from BEFORE the push (initially at rest).
End your graph when the cart is moving full speed in the opposite direction.”

Again, we haven’t talked about what energy means or the different
“flavors” of energy. I just wanted to see what notions the kids had
about this system. There was some interesting discussion as to whether
the rubber band started with some energy before the cart even hit it.

Other things:
** By including the push in the graph, we can talk about open/closed
systems and when energy is conserved.
** I like begining with focusing on where the energy is (in terms of
the objects) rather than the flavors of energy (kinetic, elastic,
etc). Kinda reminds me about whether we label forces like Fg or
Fearth. I think starting with objects lends some concreteness to it.

Day 10: Energy Intro

"On a group whiteboard, please answer these questions:
(1) What do you observe?
(2) What do you think might be happening?"

In one class, every group said energy transfers from one pendulum to the other and back again. In my other class, each group said something different: force caused motion to transfer, energy transferred, vibration transferred, forces interacted, something about weight, and something about inertia?? (pendulum on left was at rest until right pendulum acted on it).

In the first class, I asked them to make an energy pie chart…and no sooner had I said "pie" when a student immediately said "Wouldn't a line graph be better since it's changing over time?" So I ran with it, and skipped pies in the second class and went steady to the line graph.

I asked for two lines on the graph, one for each pendulum. Later, I asked them to add a line that represented the sum of the energies.

Pictured is one group's work.

(Note: We haven't defined energy in class yet. I just wanted to see where they are new and what they would draw. One student realized we didn't have a way to measure energy yet, so we were arguing over something we couldn't verify…

Yet!)

Day 9: Elevator Distances

In AP Physics C today, we rode the elevator while standing on a force plate. Using the force vs. time data, can you figure out the distance between the top and bottom floors? (Hint: Use the momentum principle.)

Day 8: Computerized Preassessments and XKCD Passwords

Administered the FCI online via WebAssign today. This was also their first time using WebAssign. In the past, I had kids enroll themselves in WebAsssign using a class key, but students would often forget their username and password. So this time, I created the accounts myself, using their school email handle as their username and a random 3-word password (ala xkcd). It was a neat way to work that famous xkcd comic into class and make it meaningful.

See http://xkcd.com/936/ and http://preshing.com/20110811/xkcd-password-generator

Day 7: Gallery Walk

Rather than having each group present their whiteboard problems, students circulated around the room and checked their work. Discussion afterward if students had questions.

Day 6: Ball Bounce Redeux

Students took more data and graphs for the ball bounce lab. (Only 1 group made a graph the first time.) New challenge tomorrow using their new bounce data.