The math in a hybrid car

For an end of the semester project in my physics classes, I posed the following question to my students:

If you put 100,000 miles on a car, which is a better deal, a hybrid or a traditional car?

Students were asked to look up a car they would be interested in buying, but the car has to come in both hybrid and traditional engine models. They were asked to look at the price of the car and the cost of gas over the 100,000 mile “life” of the car (OK, some are going to sell it at 50K, and others hold onto it until it dies, but 10,000 seemed like a good average). We just finished a unit on energy, and I thought this would be a good way to get them thinking about energy and money.

If you want to know their results, you’ll have to keep reading, but I’ve since had time to think about making this question more open-ended, inquiry (thanks to Dy/Dan for keeping my on my inquiry toes). So now I’m thinking of the questions that could be raised in a class discussion:

  • Write an equation for the cost of each car as a function of the miles driven.
  • Using these two equations, solve for the intersection of the lines. What does this intersection represent?
  • Car mileage is rated in both highway and city. Expand your equation to include a variable for the percent of driving that is city.
  • How many extra fill-ups will it take to drive the traditional engine car? If your time is worth money, how much will this cost you if you make $50,000/year?
  • How much gas is saved by driving the hybrid? What percent is this?

The list can go much further than this. Leave it up to your students to develop more.

Oh, the answer.

Students did calculations from the Honda Civic to the Cadillac Escalade (yes, it comes in a hybrid). None of the hybrids broke even with the traditional engine in cost for 100,000 miles. Students were asked to write a short paragraph saying if they thought buying the hybrid was “worth it.” They gave great responses, including those who even looked at the gas they would save just from switching from the car they are now driving to a more fuel efficient car (one student said it wasn’t worth it to buy the hybrid, but certainly was worth it–financially and environmentally–to buy a new car to upgrade her mileage.

Free shoppping?

It’s that time again. Time to wander the aisles of the college town “free stores.”

These stores don’t pay rent, and the aisles move daily (if not hourly). The merchandise are the items the students don’t feel like taking with them. Walk around student neighborhoods as finals and graduation come to an end, and you’ll find all sorts of treasures. A couple months ago I got a “new” CD/tape/radio player that a neighbor had nicely set out on the curb (replaced with an iPod and speakers?). Then, a couple bike wheels. Today, a nice hand-vacuum.

So, help keep these items from the scrapbin of history; give them another life in your house.

The 15th Annual Bike to Work Day is Thursday, May 14th, 2009

The San Francisco Bay Area’s 15th Annual Bike to Work Day will take place on Thursday, May 14, 2009. Bike to Work Day is the premier bicycling event taking place in all of Northern California with all nine Bay Area counties participating in the celebration. The event is just one day of many events taking place in May as part of National Bike Month.

Complete details here:

Peets or Starbucks? An organic coffee review

[Note: This review is over eight years old. I hoped to update it, but haven’t got around to it]

Yesterday I stopped by my local Peets (Walnut and Vine, the original) to see if they had organic decaf beans (about 7:00 pm, very slow inside). The bean counter worker looked at the selection and said “No, not certified, but they’re all basically organic except for the certification.”

I said thanks and left the store, but a few doors away I was upset enough about his response that I decided to go back. I asked him what he had meant by “basically organic.” He said that they don’t really use any pesticides, that Peets is careful who they buy coffee from, and implied that therefore they used no/fewer pesticides. I asked if he could show me this in writing, and he went in the back to see. When he came out, he said they had nothing. I asked if the manager was in, and he went and got someone.

The shift leader (“I’m not the manager”) repeated his claim that all the beans are grown with “almost no pesticides.” I again asked if they had this in writing. She said no, but that was what they were told in trainings. (Peets website “Lean: How Coffee is Grown” make no mention of pesticides or organic farming practices.) I left with three of the workers there wishing me a good evening in tones that didn’t seem to convey any real sense of sincerity.

After this experience, I thought I’d see what response I got at the Starbucks down the street (Cedar and Shattuck, “Mortuary Mall” for those who’ve been in town a while). I asked if they had any organic decaf. The woman at the counter told me that no, while they had organic beans that were decaf, the decaffeinating process made them not organic. I said that the “Swiss water process” didn’t make it not organic, and she replied that Starbucks doesn’t use the water process, and she wasn’t sure why. We had a good, short discussion about how at least the beans were being grown in an organic matter, so it was better for the farms and farmworkers, even though at the last minute some chemicals got added to it.

I must say that I was pleased about the honesty I got from the worker at Starbucks. She said that she had convinced many people to get the chemically treated, formerly organic decaf beans, but was very clear on what made them non-organic.

By the way, both companies sell organic regular coffee, just not organic decaf.

So, bad marks for both companies for not carrying organic decaf. Peets gets serious bad marks for not even admitting that their coffee isn’t organic unless they can say so in writing, essentially trying to sell me that there’s no real difference except for the label, what I would consider deceitful marketing–and this all the way up to the top person in the store. Good marks to Starbucks for honesty and knowing what actually happens to their beans, and not trying to sell some that weren’t grown organically as “almost organic.”

Carbon sequestering in the seabed, nice video too

Science Friday, my favorite radio show when I’m not teaching on Fridays, had a great piece today on carbon sequestering on the ocean floor.

What if you could take CO2, pump it down a deep hole in the sea floor and turn it into something harmless? New research suggests the idea is not so far-fetched. David Goldberg, Taro Takahashi and Angela Slagle of Lamont-Doherty Earth Observatory published a study on the subject in the Proceedings of the National Academy of Sciences this week.

Click the “Play” arrow on the lower left side to start the video. It does a great job of using breakfast cereals to help explain the process.