Solving ‘roller coaster’ energy problems

Step-by-step instructions.

Try to complete each section on your own before you move to the next image. Each slide shows the answer to the preceding question.

1. First, examine the problem and determine the energy storage types involved.

Slide showing the roller coasterThis problem consists of a roller coaster which has a chain that pulls the car to the top of the first hill. The problem defines the system as frictionless (μ = 0), and insignificant air resistance.
Before you go on, define the system, then draw axes for your energy diagrams at each point with a letter (don’t worry about the number of blocks of each energy storage yet). Continue reading “Solving ‘roller coaster’ energy problems”

Back to School Night – Menlo-Atherton HS, 2017

image of back to school night home pageOK, maybe I’m in the minority, but I really like Back to School Nights. I appreciate the parents taking time out of their busy lives to come in and get a sense of who is teaching their students.

Tonight was no different. Great parents, lots of appreciation expressed, and a few good questions thrown in (not much time in ten minutes to ask questions).

Unfortunately, as usual, the higher academic classes have higher turnout of parents. Why? I can speculate about amount of free time, ability to get off work early, etc. But in the end, I don’t think it’s anyone’s fault (I suspect that all parents want their kids to be successful in school), it’s just a reality.

Thanks to all the parents who did make it out (and thanks to all those who didn’t for trusting your students in my care).

Here are handouts of the slides I used:


Modeling Instruction and NGSS: Energy as a Crosscutting Concept

NGSS 3D learning logo

At the January 2017 Lasallian Symposium at St. Mary’s College in Moraga, CA, I presented a short talk describing how Modeling Instruction uses energy as a Crosscutting Concept for implementing the Next Generation Science Standards. You can download a copy of the slides from my talk here.

Video (without narration)

Physics/Chemistry of Espresso Machines: Part 1

Diagram showing how steam and water escape the water tank at two different locations.

Here’s an activity based on observing espresso machines in action. Watch the following video showing the milk steaming container (with a short sidetrack to the espresso pot).

What do you notice about the milk as it steams? Can you explain what is happening?

Diagram showing how steam and water escape the water tank at two different locations.Here are some details of how this espresso machine works:

  • The water boiling tank is filled about ¾ of the way up with water.
  • From the bottom of the water tank, a tube runs upward to the coffee holder, where the water is forced through the coffee grounds and drips down into the espresso pot.
  • At the top of the water tank, a tube leads outside to the steamer jet, which is placed in the milk steaming container.

The answers aren’t here, you need to develop them yourselves 🙂

Hints below ↓










Notice that for the first 20-30 seconds, there are bubbles forming, but after that there are no more bubble forming.

More hints below ↓










What is in the space above the water when the machine first starts? What is in that space after 20-30 seconds?

Introduction to Modeling Workshops at NSTA in Reno

Yesterday, I lead two short workshops on Modeling Instruction at the National Science Teachers Association area conference in Reno, Nevada. About 30 people attended the first one, and about 20 the second (about half of whom had been at the first one as well). As in many good physics activities, this included going outside (the floor in the conference room was carpeted, so the balls didn’t bounce well on it).

  • In the first workshop, I introduced the Bouncing Ball lab, which offers an introductory activity that focuses on developing students’ understanding of lab design and data analysis.
  • The second workshop introduced the Buggy Lab, that helps students develop a model for constant velocity motion.

Here are my PowerPoint slides: PPTX format with video links on in PDF format.

Here are some images:

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180: Day 26: How does GPS work?

students creating scale models of GPS satellite orbits

Two summers ago I was able to attend the Einstein Plus workshop at the Perimeter Institute for Theoretical Physics. They provided some great mini-units on ‘Modern Physics’ topics, and I’ve tried to figure out a way to integrate these into my class. This year I realized I could use them as “filler” during our seniors’ Kairos retreats (students are gone for three days, which means I don’t see some of them all week!). I’m pulling out a couple of days worth of work from each unit, and the students who are on the retreat don’t have to make it up (they always have too much to make up anyway). This way, each student will get four mini-units, and miss one.

Today we started Everyday Einstein: GPS & Relativity. Students watch a short video about GPS (8 minutes), then explore uses of GPS, create scale drawings of the GPS satellites above the earth, make some calculations about the time between signal broadcast and its arrival on earth, and finally use an online mapping site to triangulate the position of an object given three cities and distances (would work great for earthquake epicenter location as well). We didn’t get as far as I had hoped, but we can finish the geolocating tomorrow, then start on relativity.

students creating scale models of GPS satellite orbits
Students drawing scale models of the height of GPS satellites vs radius of earth. One group also added the International Space Station, and, with prompting, added the height of the atmosphere.

180: Day 25: Faculty/staff retreat

Lee's sketch from Mont La Salle

Today we had a faculty/staff retreat at Mont La Salle at the Christian Brothers Retreat and Conference Center in Napa, CA. During the welcome/introduction, our principal suggested that we turn off our phones for the four hours. I thought that sounded like a good idea, and turned mine off. Reflecting on our sense of “need” to be connected, I thought about emergencies that might happen that might need my attention, but I couldn’t come up with any that couldn’t wait the four hours. After all, a couple of decades ago I did not expect people to be able to contact me 24/7, so why can’t I do that now?

During a break-out session, I had an hour to do some journaling/reflection, and found a nice shady spot with a beautiful view of the hills of the Napa Valley. My first thought was to take a photo, but then I realized that would require me to turn on my phone. Now, I’m no sketching artist, but I took this as an opportunity to try out some sketching. Attached is the sketch I made. It’s not really to scale, and isn’t in ‘millions of colors,’ but I can look at it and remember where I was–and isn’t that one of the main points of a photograph?

Lee's sketch from Mont La Salle

180: Day 24: Fundraising for the whole school

SHCP 2015 Walkathon image

Most schools these days need to do fundraising, whether they be public or private. The last two weeks at Sacred Heart Cathedral has been “Walkathon weeks.” Students collect donations from relatives, neighbors, and friends. It’s our one big student fundraiser of the year. The final day is the Walkathon itself. Students meet at the Polo Fields in Golden Gate Park. After taking roll and some spirit-building games, we’re off on the walk. Four miles later, we’re back in the bleachers for a bit more spirit, then everyone walks to the nearby meadow for lunch. After lunch, students and teachers are free to go.

I enjoyed the walkathon, and think it’s a great opportunity for community building (as well as to make some money). Having a full day (well, half-day in reality) where our community gets together without academics or athletics gives us a chance to chat and just enjoy life together. The parent volunteers are wonderful, and lunch is a great finisher for the day (they even had plenty of vegi-burgers!). Since they have the afternoon off, I heard about some of the students were heading down to the beach (September in San Francisco tend to have the most sun, and we lucked out this weekend).

This might be harder for a public school to pull 0ff (in California, there is a minimum number of hours required to make a day count as a “full day” for finances), but I think it could be done. SHC has worked out many details in 26 years; if you’re interested in more details, here’s the Walkathon home page, or leave a question in the comments section below.

It will be a great day when we don’t have to have fundraisers in schools, but in the mean time, this model is a great one.

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180: Day 21: Final suggestions/tips for buggy collision challenge.

photo of students determining the speed of their buggy.

Buggy collision prediction sheet lined up with a meter stick.Last blocks with buggies: Here’s another close up of the target sheets I use with my students. The complete the top, then find where on the row of four metersticks they need to place their prediction. I give not help at this point, and often ask “Are you sure it’s in the right place?” (even when it is). I try to involve all six to eight students in the trial (two combined groups of 3-4 each). When they are done, there is homework for them to work on in class.

A few tips:

  • Even with only four or five tests required (eight to ten groups), there is still down time for many students, so make sure you have something else for them to do. I always have that day’s worksheet/night’s homework ready for them. Next year, I plan to have something more in line with a conclusion on the lab.
  • My target has a very low “A” range, so, as I said yesterday, any group that lands on the paper gets an A.
  • Have them measure and calculate the speed of their buggy on the day of the collision test. This should take about five minutes, then ten minutes to make their prediction. If they use speeds from previous days, the batteries may have weakened and slowed the buggy down.
  • Use the “testing” time with your small groups to confirm they understand the placement of their paper. I often ask “Does this position make sense?”–to which they should answer “Yes, because the fast car will move a greater distance” or something along this line.
photo of students determining the speed of their buggy.
Students making measurements to determine the speed of their car right before the collision challenge.

180: Day 20: “One train leave a station at 2:30, and another train leaves…

Buggy collision prediction sheet lined up with a meter stick.

Here’s a classic physics problem:

One train leaves a station at 2:30 at a speed of 40 m/s,
and a second train leaves another station at 50 m/s.
The stations are 40 km apart, and the trains are heading
toward each other. At what time and position will the
trains collide?

These days, many teachers use this as a chance for an actual experiment. I challenge my students to determine the speed of their cars, then I match them up with a random group (well I know each group has a car with a different speed). They then need to calculate the position the cars will collide if they start four meters apart. I have a grade sheet that shows them their grade. My standard sheet has A-D on it, with A at the center where the cars are due to collide.

With each buggies traveling 1.2-3.8 meters, I probably should give them a bit more slack in the “A” range, so I’m thinking that for next year I may use three sheets of paper with most of the center one being the “A”, and the outside ones being B-D.

I like this lab because it’s easy to get correct predictions, and students have to go back and check their math if they don’t get an “A”.

Here’s a video showing an accurate prediction. The class, and I, get quite excited as the collision moment approaches!